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Groups > linux.kernel > #1373475 > unrolled thread

[PATCH 0/11] introduce down_write_killable for rw_semaphore v3

Started byMichal Hocko <mhocko@kernel.org>
First post2016-04-07 17:20 +0200
Last post2016-04-12 20:10 +0200
Articles 18 — 4 participants

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Contents

  [PATCH 0/11] introduce down_write_killable for rw_semaphore v3 Michal Hocko <mhocko@kernel.org> - 2016-04-07 17:20 +0200
    [PATCH 01/11] locking, rwsem: get rid of __down_write_nested Michal Hocko <mhocko@kernel.org> - 2016-04-07 17:20 +0200
      [tip:locking/rwsem] locking/rwsem: Get rid of __down_write_nested() tip-bot for Michal Hocko <tipbot@zytor.com> - 2016-04-13 13:40 +0200
    [PATCH 04/11] sh, rwsem: drop superfluous arch specific implementation Michal Hocko <mhocko@kernel.org> - 2016-04-07 17:20 +0200
      [tip:locking/rwsem] locking/rwsem, sh: Drop superfluous arch  specific implementation tip-bot for Michal Hocko <tipbot@zytor.com> - 2016-04-13 13:40 +0200
    [PATCH 02/11] locking, rwsem: drop explicit memory barriers Michal Hocko <mhocko@kernel.org> - 2016-04-07 17:20 +0200
      [tip:locking/rwsem] locking/rwsem: Drop explicit memory barriers tip-bot for Michal Hocko <tipbot@zytor.com> - 2016-04-13 13:40 +0200
    [PATCH 06/11] locking, rwsem: introduce basis for down_write_killable Michal Hocko <mhocko@kernel.org> - 2016-04-07 17:30 +0200
      [tip:locking/rwsem] locking/rwsem: Introduce basis for  down_write_killable() tip-bot for Michal Hocko <tipbot@zytor.com> - 2016-04-13 13:40 +0200
    [PATCH 11/11] locking, rwsem: provide down_write_killable Michal Hocko <mhocko@kernel.org> - 2016-04-07 17:30 +0200
    [PATCH 08/11] ia64, rwsem: provide __down_write_killable Michal Hocko <mhocko@kernel.org> - 2016-04-07 17:30 +0200
      Re: [PATCH 08/11] ia64, rwsem: provide __down_write_killable Sergei Shtylyov <sergei.shtylyov@cogentembedded.com> - 2016-04-07 19:30 +0200
        Re: [PATCH 08/11] ia64, rwsem: provide __down_write_killable Michal Hocko <mhocko@kernel.org> - 2016-04-08 08:30 +0200
    [PATCH 03/11] xtensa, rwsem: drop superfluous arch specific implementation Michal Hocko <mhocko@kernel.org> - 2016-04-07 17:30 +0200
      [tip:locking/rwsem] locking/rwsem, xtensa: Drop superfluous arch  specific implementation tip-bot for Michal Hocko <tipbot@zytor.com> - 2016-04-13 13:40 +0200
    Re: [PATCH 0/11] introduce down_write_killable for rw_semaphore v3 Michal Hocko <mhocko@kernel.org> - 2016-04-12 11:40 +0200
      Re: [PATCH 0/11] introduce down_write_killable for rw_semaphore v3 Peter Zijlstra <peterz@infradead.org> - 2016-04-12 17:50 +0200
        Re: [PATCH 0/11] introduce down_write_killable for rw_semaphore v3 Michal Hocko <mhocko@kernel.org> - 2016-04-12 20:10 +0200

#1373475 — [PATCH 0/11] introduce down_write_killable for rw_semaphore v3

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-07 17:20 +0200
Subject[PATCH 0/11] introduce down_write_killable for rw_semaphore v3
Message-ID<rljSW-5SJ-5@gated-at.bofh.it>
Hi,
the following patchset implements a killable variant of write lock
for rw_semaphore. My usecase is to turn as many mmap_sem write users
to use a killable variant which will be helpful for the oom_reaper
merged in 4.6-rc1 (aac453635549 ("mm, oom: introduce oom reaper")) to
asynchronously tear down the oom victim address space which requires
mmap_sem for read. This will reduce a likelihood of OOM livelocks caused
by oom victim being stuck on a lock or other resource which prevents it
to reach its exit path and release the memory. I haven't implemented the
killable variant of the read lock because I do not have any usecase for
this API.

The previous version of this series was posted [1]. I have dropped patches 7-9
based on Davidlohr Bueso feedback because he pointed out that sh and extensa
can use the generic implementation. Further investigation has shown the same
is true for sparc. While those patches were removed 3 new ones were added for
same archs to use the generic implementation. Other than that there were no
functional changes since the last version.

The patchset is organized as follows.
- Patch 1 is a trivial cleanup
- Patch 2, I belive, shouldn't introduce any functional changes as per
  Documentation/memory-barriers.txt.
- Patches 3-5 are moving xtensa, sh and sparc to generic implementation
- Patch 6 is the preparatory work and necessary infrastructure for
  down_write_killable. It implements generic __down_write_killable
  and prepares the write lock slow path to bail out earlier when told so
- Patch 7-10 are implementing arch specific __down_write_killable. One
  patch per architecture.
- finally patch 11 implements down_write_killable and ties everything
  together. I am not really an expert on lockdep so I hope I got it right.

Follow up patches to change mmap_sem write users to killable form is not
part of the series because that will be routed via mmotm tree later on.

I have tested on x86 with OOM situations with high mmap_sem contention
(basically many parallel page faults racing with many parallel mmap/munmap
tight loops) so the waiters for the write locks are routinely interrupted
by SIGKILL.

Thanks!
---
[1] http://lkml.kernel.org/r/1459508695-14915-1-git-send-email-mhocko@kernel.org

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#1373477 — [PATCH 01/11] locking, rwsem: get rid of __down_write_nested

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-07 17:20 +0200
Subject[PATCH 01/11] locking, rwsem: get rid of __down_write_nested
Message-ID<rljSX-5SJ-35@gated-at.bofh.it>
In reply to#1373475
From: Michal Hocko <mhocko@suse.com>

This is no longer used anywhere and all callers (__down_write) use
0 as a subclass. Ditch __down_write_nested to make the code easier
to follow.

This shouldn't introduce any functional change.

Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 arch/s390/include/asm/rwsem.h   | 7 +------
 arch/sh/include/asm/rwsem.h     | 5 -----
 arch/sparc/include/asm/rwsem.h  | 7 +------
 arch/x86/include/asm/rwsem.h    | 7 +------
 include/asm-generic/rwsem.h     | 7 +------
 include/linux/rwsem-spinlock.h  | 1 -
 kernel/locking/rwsem-spinlock.c | 7 +------
 7 files changed, 5 insertions(+), 36 deletions(-)

diff --git a/arch/s390/include/asm/rwsem.h b/arch/s390/include/asm/rwsem.h
index 4b43ee7e6776..8e52e72f3efc 100644
--- a/arch/s390/include/asm/rwsem.h
+++ b/arch/s390/include/asm/rwsem.h
@@ -90,7 +90,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
+static inline void __down_write(struct rw_semaphore *sem)
 {
 	signed long old, new, tmp;
 
@@ -108,11 +108,6 @@ static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 		rwsem_down_write_failed(sem);
 }
 
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	__down_write_nested(sem, 0);
-}
-
 /*
  * trylock for writing -- returns 1 if successful, 0 if contention
  */
diff --git a/arch/sh/include/asm/rwsem.h b/arch/sh/include/asm/rwsem.h
index edab57265293..a5104bebd1eb 100644
--- a/arch/sh/include/asm/rwsem.h
+++ b/arch/sh/include/asm/rwsem.h
@@ -114,11 +114,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 		rwsem_downgrade_wake(sem);
 }
 
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
-{
-	__down_write(sem);
-}
-
 /*
  * implement exchange and add functionality
  */
diff --git a/arch/sparc/include/asm/rwsem.h b/arch/sparc/include/asm/rwsem.h
index 069bf4d663a1..e5a0d575bc7f 100644
--- a/arch/sparc/include/asm/rwsem.h
+++ b/arch/sparc/include/asm/rwsem.h
@@ -45,7 +45,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
+static inline void __down_write(struct rw_semaphore *sem)
 {
 	long tmp;
 
@@ -55,11 +55,6 @@ static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 		rwsem_down_write_failed(sem);
 }
 
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	__down_write_nested(sem, 0);
-}
-
 static inline int __down_write_trylock(struct rw_semaphore *sem)
 {
 	long tmp;
diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
index cad82c9c2fde..d79a218675bc 100644
--- a/arch/x86/include/asm/rwsem.h
+++ b/arch/x86/include/asm/rwsem.h
@@ -99,7 +99,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
+static inline void __down_write(struct rw_semaphore *sem)
 {
 	long tmp;
 	asm volatile("# beginning down_write\n\t"
@@ -116,11 +116,6 @@ static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 		     : "memory", "cc");
 }
 
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	__down_write_nested(sem, 0);
-}
-
 /*
  * trylock for writing -- returns 1 if successful, 0 if contention
  */
diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
index d6d5dc98d7da..b8d8a6cf4ca8 100644
--- a/include/asm-generic/rwsem.h
+++ b/include/asm-generic/rwsem.h
@@ -53,7 +53,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
+static inline void __down_write(struct rw_semaphore *sem)
 {
 	long tmp;
 
@@ -63,11 +63,6 @@ static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 		rwsem_down_write_failed(sem);
 }
 
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	__down_write_nested(sem, 0);
-}
-
 static inline int __down_write_trylock(struct rw_semaphore *sem)
 {
 	long tmp;
diff --git a/include/linux/rwsem-spinlock.h b/include/linux/rwsem-spinlock.h
index 561e8615528d..a733a5467e6c 100644
--- a/include/linux/rwsem-spinlock.h
+++ b/include/linux/rwsem-spinlock.h
@@ -34,7 +34,6 @@ struct rw_semaphore {
 extern void __down_read(struct rw_semaphore *sem);
 extern int __down_read_trylock(struct rw_semaphore *sem);
 extern void __down_write(struct rw_semaphore *sem);
-extern void __down_write_nested(struct rw_semaphore *sem, int subclass);
 extern int __down_write_trylock(struct rw_semaphore *sem);
 extern void __up_read(struct rw_semaphore *sem);
 extern void __up_write(struct rw_semaphore *sem);
diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c
index 3a5048572065..bab26104a5d0 100644
--- a/kernel/locking/rwsem-spinlock.c
+++ b/kernel/locking/rwsem-spinlock.c
@@ -191,7 +191,7 @@ int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * get a write lock on the semaphore
  */
-void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
+void __sched __down_write(struct rw_semaphore *sem)
 {
 	struct rwsem_waiter waiter;
 	struct task_struct *tsk;
@@ -227,11 +227,6 @@ void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
 	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 }
 
-void __sched __down_write(struct rw_semaphore *sem)
-{
-	__down_write_nested(sem, 0);
-}
-
 /*
  * trylock for writing -- returns 1 if successful, 0 if contention
  */
-- 
2.8.0.rc3

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#1377789 — [tip:locking/rwsem] locking/rwsem: Get rid of __down_write_nested()

Fromtip-bot for Michal Hocko <tipbot@zytor.com>
Date2016-04-13 13:40 +0200
Subject[tip:locking/rwsem] locking/rwsem: Get rid of __down_write_nested()
Message-ID<rnrjk-x5-19@gated-at.bofh.it>
In reply to#1373477
Commit-ID:  f8e04d854506ddfeba9cb41b601972b28521f104
Gitweb:     http://git.kernel.org/tip/f8e04d854506ddfeba9cb41b601972b28521f104
Author:     Michal Hocko <mhocko@suse.com>
AuthorDate: Thu, 7 Apr 2016 17:12:21 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 13 Apr 2016 10:42:16 +0200

locking/rwsem: Get rid of __down_write_nested()

This is no longer used anywhere and all callers (__down_write()) use
0 as a subclass. Ditch __down_write_nested() to make the code easier
to follow.

This shouldn't introduce any functional change.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Signed-off-by: Jason Low <jason.low2@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-alpha@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: linux-xtensa@linux-xtensa.org
Cc: sparclinux@vger.kernel.org
Link: http://lkml.kernel.org/r/1460041951-22347-2-git-send-email-mhocko@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/s390/include/asm/rwsem.h   | 7 +------
 arch/sh/include/asm/rwsem.h     | 5 -----
 arch/sparc/include/asm/rwsem.h  | 7 +------
 arch/x86/include/asm/rwsem.h    | 7 +------
 include/asm-generic/rwsem.h     | 7 +------
 include/linux/rwsem-spinlock.h  | 1 -
 kernel/locking/rwsem-spinlock.c | 7 +------
 7 files changed, 5 insertions(+), 36 deletions(-)

diff --git a/arch/s390/include/asm/rwsem.h b/arch/s390/include/asm/rwsem.h
index fead491..555d23b 100644
--- a/arch/s390/include/asm/rwsem.h
+++ b/arch/s390/include/asm/rwsem.h
@@ -90,7 +90,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
+static inline void __down_write(struct rw_semaphore *sem)
 {
 	signed long old, new, tmp;
 
@@ -108,11 +108,6 @@ static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 		rwsem_down_write_failed(sem);
 }
 
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	__down_write_nested(sem, 0);
-}
-
 /*
  * trylock for writing -- returns 1 if successful, 0 if contention
  */
diff --git a/arch/sh/include/asm/rwsem.h b/arch/sh/include/asm/rwsem.h
index edab572..a5104be 100644
--- a/arch/sh/include/asm/rwsem.h
+++ b/arch/sh/include/asm/rwsem.h
@@ -114,11 +114,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 		rwsem_downgrade_wake(sem);
 }
 
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
-{
-	__down_write(sem);
-}
-
 /*
  * implement exchange and add functionality
  */
diff --git a/arch/sparc/include/asm/rwsem.h b/arch/sparc/include/asm/rwsem.h
index 069bf4d..e5a0d57 100644
--- a/arch/sparc/include/asm/rwsem.h
+++ b/arch/sparc/include/asm/rwsem.h
@@ -45,7 +45,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
+static inline void __down_write(struct rw_semaphore *sem)
 {
 	long tmp;
 
@@ -55,11 +55,6 @@ static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 		rwsem_down_write_failed(sem);
 }
 
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	__down_write_nested(sem, 0);
-}
-
 static inline int __down_write_trylock(struct rw_semaphore *sem)
 {
 	long tmp;
diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
index ceec86eb..4a8292a 100644
--- a/arch/x86/include/asm/rwsem.h
+++ b/arch/x86/include/asm/rwsem.h
@@ -99,7 +99,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
+static inline void __down_write(struct rw_semaphore *sem)
 {
 	long tmp;
 	asm volatile("# beginning down_write\n\t"
@@ -116,11 +116,6 @@ static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 		     : "memory", "cc");
 }
 
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	__down_write_nested(sem, 0);
-}
-
 /*
  * trylock for writing -- returns 1 if successful, 0 if contention
  */
diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
index d6d5dc9..b8d8a6c 100644
--- a/include/asm-generic/rwsem.h
+++ b/include/asm-generic/rwsem.h
@@ -53,7 +53,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
+static inline void __down_write(struct rw_semaphore *sem)
 {
 	long tmp;
 
@@ -63,11 +63,6 @@ static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 		rwsem_down_write_failed(sem);
 }
 
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	__down_write_nested(sem, 0);
-}
-
 static inline int __down_write_trylock(struct rw_semaphore *sem)
 {
 	long tmp;
diff --git a/include/linux/rwsem-spinlock.h b/include/linux/rwsem-spinlock.h
index 561e861..a733a54 100644
--- a/include/linux/rwsem-spinlock.h
+++ b/include/linux/rwsem-spinlock.h
@@ -34,7 +34,6 @@ struct rw_semaphore {
 extern void __down_read(struct rw_semaphore *sem);
 extern int __down_read_trylock(struct rw_semaphore *sem);
 extern void __down_write(struct rw_semaphore *sem);
-extern void __down_write_nested(struct rw_semaphore *sem, int subclass);
 extern int __down_write_trylock(struct rw_semaphore *sem);
 extern void __up_read(struct rw_semaphore *sem);
 extern void __up_write(struct rw_semaphore *sem);
diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c
index 3a50485..bab2610 100644
--- a/kernel/locking/rwsem-spinlock.c
+++ b/kernel/locking/rwsem-spinlock.c
@@ -191,7 +191,7 @@ int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * get a write lock on the semaphore
  */
-void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
+void __sched __down_write(struct rw_semaphore *sem)
 {
 	struct rwsem_waiter waiter;
 	struct task_struct *tsk;
@@ -227,11 +227,6 @@ void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
 	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 }
 
-void __sched __down_write(struct rw_semaphore *sem)
-{
-	__down_write_nested(sem, 0);
-}
-
 /*
  * trylock for writing -- returns 1 if successful, 0 if contention
  */

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#1373478 — [PATCH 04/11] sh, rwsem: drop superfluous arch specific implementation

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-07 17:20 +0200
Subject[PATCH 04/11] sh, rwsem: drop superfluous arch specific implementation
Message-ID<rljSX-5SJ-37@gated-at.bofh.it>
In reply to#1373475
From: Michal Hocko <mhocko@suse.com>

since "locking, rwsem: drop explicit memory barriers" the arch specific
code is basically same as the the generic one so we can drop the
superfluous code.

Suggested-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 arch/sh/include/asm/Kbuild  |   1 +
 arch/sh/include/asm/rwsem.h | 117 --------------------------------------------
 2 files changed, 1 insertion(+), 117 deletions(-)
 delete mode 100644 arch/sh/include/asm/rwsem.h

diff --git a/arch/sh/include/asm/Kbuild b/arch/sh/include/asm/Kbuild
index aac452b26aa8..6d866c7a9b74 100644
--- a/arch/sh/include/asm/Kbuild
+++ b/arch/sh/include/asm/Kbuild
@@ -25,6 +25,7 @@ generic-y += percpu.h
 generic-y += poll.h
 generic-y += preempt.h
 generic-y += resource.h
+generic-y += rwsem.h
 generic-y += sembuf.h
 generic-y += serial.h
 generic-y += shmbuf.h
diff --git a/arch/sh/include/asm/rwsem.h b/arch/sh/include/asm/rwsem.h
deleted file mode 100644
index f6c951c7a875..000000000000
--- a/arch/sh/include/asm/rwsem.h
+++ /dev/null
@@ -1,117 +0,0 @@
-/*
- * include/asm-sh/rwsem.h: R/W semaphores for SH using the stuff
- * in lib/rwsem.c.
- */
-
-#ifndef _ASM_SH_RWSEM_H
-#define _ASM_SH_RWSEM_H
-
-#ifndef _LINUX_RWSEM_H
-#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
-#endif
-
-#ifdef __KERNEL__
-
-#define RWSEM_UNLOCKED_VALUE		0x00000000
-#define RWSEM_ACTIVE_BIAS		0x00000001
-#define RWSEM_ACTIVE_MASK		0x0000ffff
-#define RWSEM_WAITING_BIAS		(-0x00010000)
-#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
-#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
-
-/*
- * lock for reading
- */
-static inline void __down_read(struct rw_semaphore *sem)
-{
-	if (atomic_inc_return((atomic_t *)(&sem->count)) <= 0)
-		rwsem_down_read_failed(sem);
-}
-
-static inline int __down_read_trylock(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	while ((tmp = sem->count) >= 0) {
-		if (tmp == cmpxchg(&sem->count, tmp,
-				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			return 1;
-		}
-	}
-	return 0;
-}
-
-/*
- * lock for writing
- */
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
-				(atomic_t *)(&sem->count));
-	if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
-		rwsem_down_write_failed(sem);
-}
-
-static inline int __down_write_trylock(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
-		      RWSEM_ACTIVE_WRITE_BIAS);
-	return tmp == RWSEM_UNLOCKED_VALUE;
-}
-
-/*
- * unlock after reading
- */
-static inline void __up_read(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_dec_return((atomic_t *)(&sem->count));
-	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
-		rwsem_wake(sem);
-}
-
-/*
- * unlock after writing
- */
-static inline void __up_write(struct rw_semaphore *sem)
-{
-	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
-			      (atomic_t *)(&sem->count)) < 0)
-		rwsem_wake(sem);
-}
-
-/*
- * implement atomic add functionality
- */
-static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
-{
-	atomic_add(delta, (atomic_t *)(&sem->count));
-}
-
-/*
- * downgrade write lock to read lock
- */
-static inline void __downgrade_write(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
-	if (tmp < 0)
-		rwsem_downgrade_wake(sem);
-}
-
-/*
- * implement exchange and add functionality
- */
-static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
-{
-	return atomic_add_return(delta, (atomic_t *)(&sem->count));
-}
-
-#endif /* __KERNEL__ */
-#endif /* _ASM_SH_RWSEM_H */
-- 
2.8.0.rc3

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#1377798 — [tip:locking/rwsem] locking/rwsem, sh: Drop superfluous arch specific implementation

Fromtip-bot for Michal Hocko <tipbot@zytor.com>
Date2016-04-13 13:40 +0200
Subject[tip:locking/rwsem] locking/rwsem, sh: Drop superfluous arch specific implementation
Message-ID<rnrjl-x5-45@gated-at.bofh.it>
In reply to#1373478
Commit-ID:  e4a2b01ed3d1591437f93a42f6c4c039b60e0c0a
Gitweb:     http://git.kernel.org/tip/e4a2b01ed3d1591437f93a42f6c4c039b60e0c0a
Author:     Michal Hocko <mhocko@suse.com>
AuthorDate: Thu, 7 Apr 2016 17:12:24 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 13 Apr 2016 10:42:19 +0200

locking/rwsem, sh: Drop superfluous arch specific implementation

Since "locking, rwsem: drop explicit memory barriers" the arch specific
code is basically same as the the generic one so we can drop the
superfluous code.

Suggested-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Signed-off-by: Jason Low <jason.low2@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-alpha@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: linux-xtensa@linux-xtensa.org
Cc: sparclinux@vger.kernel.org
Link: http://lkml.kernel.org/r/1460041951-22347-5-git-send-email-mhocko@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/sh/include/asm/Kbuild  |   1 +
 arch/sh/include/asm/rwsem.h | 117 --------------------------------------------
 2 files changed, 1 insertion(+), 117 deletions(-)

diff --git a/arch/sh/include/asm/Kbuild b/arch/sh/include/asm/Kbuild
index a319745..751c337 100644
--- a/arch/sh/include/asm/Kbuild
+++ b/arch/sh/include/asm/Kbuild
@@ -26,6 +26,7 @@ generic-y += percpu.h
 generic-y += poll.h
 generic-y += preempt.h
 generic-y += resource.h
+generic-y += rwsem.h
 generic-y += sembuf.h
 generic-y += serial.h
 generic-y += shmbuf.h
diff --git a/arch/sh/include/asm/rwsem.h b/arch/sh/include/asm/rwsem.h
deleted file mode 100644
index f6c951c..0000000
--- a/arch/sh/include/asm/rwsem.h
+++ /dev/null
@@ -1,117 +0,0 @@
-/*
- * include/asm-sh/rwsem.h: R/W semaphores for SH using the stuff
- * in lib/rwsem.c.
- */
-
-#ifndef _ASM_SH_RWSEM_H
-#define _ASM_SH_RWSEM_H
-
-#ifndef _LINUX_RWSEM_H
-#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
-#endif
-
-#ifdef __KERNEL__
-
-#define RWSEM_UNLOCKED_VALUE		0x00000000
-#define RWSEM_ACTIVE_BIAS		0x00000001
-#define RWSEM_ACTIVE_MASK		0x0000ffff
-#define RWSEM_WAITING_BIAS		(-0x00010000)
-#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
-#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
-
-/*
- * lock for reading
- */
-static inline void __down_read(struct rw_semaphore *sem)
-{
-	if (atomic_inc_return((atomic_t *)(&sem->count)) <= 0)
-		rwsem_down_read_failed(sem);
-}
-
-static inline int __down_read_trylock(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	while ((tmp = sem->count) >= 0) {
-		if (tmp == cmpxchg(&sem->count, tmp,
-				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			return 1;
-		}
-	}
-	return 0;
-}
-
-/*
- * lock for writing
- */
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
-				(atomic_t *)(&sem->count));
-	if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
-		rwsem_down_write_failed(sem);
-}
-
-static inline int __down_write_trylock(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
-		      RWSEM_ACTIVE_WRITE_BIAS);
-	return tmp == RWSEM_UNLOCKED_VALUE;
-}
-
-/*
- * unlock after reading
- */
-static inline void __up_read(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_dec_return((atomic_t *)(&sem->count));
-	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
-		rwsem_wake(sem);
-}
-
-/*
- * unlock after writing
- */
-static inline void __up_write(struct rw_semaphore *sem)
-{
-	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
-			      (atomic_t *)(&sem->count)) < 0)
-		rwsem_wake(sem);
-}
-
-/*
- * implement atomic add functionality
- */
-static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
-{
-	atomic_add(delta, (atomic_t *)(&sem->count));
-}
-
-/*
- * downgrade write lock to read lock
- */
-static inline void __downgrade_write(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
-	if (tmp < 0)
-		rwsem_downgrade_wake(sem);
-}
-
-/*
- * implement exchange and add functionality
- */
-static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
-{
-	return atomic_add_return(delta, (atomic_t *)(&sem->count));
-}
-
-#endif /* __KERNEL__ */
-#endif /* _ASM_SH_RWSEM_H */

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#1373479 — [PATCH 02/11] locking, rwsem: drop explicit memory barriers

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-07 17:20 +0200
Subject[PATCH 02/11] locking, rwsem: drop explicit memory barriers
Message-ID<rljSX-5SJ-39@gated-at.bofh.it>
In reply to#1373475
From: Michal Hocko <mhocko@suse.com>

sh and xtensa seem to be the only architectures which use explicit
memory barriers for rw_semaphore operations even though they are not
really needed because there is the full memory barrier is always implied
by atomic_{inc,dec,add,sub}_return resp. cmpxchg. Remove them.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 arch/sh/include/asm/rwsem.h     | 14 ++------------
 arch/xtensa/include/asm/rwsem.h | 14 ++------------
 2 files changed, 4 insertions(+), 24 deletions(-)

diff --git a/arch/sh/include/asm/rwsem.h b/arch/sh/include/asm/rwsem.h
index a5104bebd1eb..f6c951c7a875 100644
--- a/arch/sh/include/asm/rwsem.h
+++ b/arch/sh/include/asm/rwsem.h
@@ -24,9 +24,7 @@
  */
 static inline void __down_read(struct rw_semaphore *sem)
 {
-	if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
-		smp_wmb();
-	else
+	if (atomic_inc_return((atomic_t *)(&sem->count)) <= 0)
 		rwsem_down_read_failed(sem);
 }
 
@@ -37,7 +35,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 	while ((tmp = sem->count) >= 0) {
 		if (tmp == cmpxchg(&sem->count, tmp,
 				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			smp_wmb();
 			return 1;
 		}
 	}
@@ -53,9 +50,7 @@ static inline void __down_write(struct rw_semaphore *sem)
 
 	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 				(atomic_t *)(&sem->count));
-	if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
-		smp_wmb();
-	else
+	if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
 		rwsem_down_write_failed(sem);
 }
 
@@ -65,7 +60,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
 
 	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 		      RWSEM_ACTIVE_WRITE_BIAS);
-	smp_wmb();
 	return tmp == RWSEM_UNLOCKED_VALUE;
 }
 
@@ -76,7 +70,6 @@ static inline void __up_read(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_dec_return((atomic_t *)(&sem->count));
 	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
 		rwsem_wake(sem);
@@ -87,7 +80,6 @@ static inline void __up_read(struct rw_semaphore *sem)
  */
 static inline void __up_write(struct rw_semaphore *sem)
 {
-	smp_wmb();
 	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 			      (atomic_t *)(&sem->count)) < 0)
 		rwsem_wake(sem);
@@ -108,7 +100,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 	if (tmp < 0)
 		rwsem_downgrade_wake(sem);
@@ -119,7 +110,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
  */
 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 {
-	smp_mb();
 	return atomic_add_return(delta, (atomic_t *)(&sem->count));
 }
 
diff --git a/arch/xtensa/include/asm/rwsem.h b/arch/xtensa/include/asm/rwsem.h
index 249619e7e7f2..593483f6e1ff 100644
--- a/arch/xtensa/include/asm/rwsem.h
+++ b/arch/xtensa/include/asm/rwsem.h
@@ -29,9 +29,7 @@
  */
 static inline void __down_read(struct rw_semaphore *sem)
 {
-	if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
-		smp_wmb();
-	else
+	if (atomic_add_return(1,(atomic_t *)(&sem->count)) <= 0)
 		rwsem_down_read_failed(sem);
 }
 
@@ -42,7 +40,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 	while ((tmp = sem->count) >= 0) {
 		if (tmp == cmpxchg(&sem->count, tmp,
 				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			smp_wmb();
 			return 1;
 		}
 	}
@@ -58,9 +55,7 @@ static inline void __down_write(struct rw_semaphore *sem)
 
 	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 				(atomic_t *)(&sem->count));
-	if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
-		smp_wmb();
-	else
+	if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
 		rwsem_down_write_failed(sem);
 }
 
@@ -70,7 +65,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
 
 	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 		      RWSEM_ACTIVE_WRITE_BIAS);
-	smp_wmb();
 	return tmp == RWSEM_UNLOCKED_VALUE;
 }
 
@@ -81,7 +75,6 @@ static inline void __up_read(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
 	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
 		rwsem_wake(sem);
@@ -92,7 +85,6 @@ static inline void __up_read(struct rw_semaphore *sem)
  */
 static inline void __up_write(struct rw_semaphore *sem)
 {
-	smp_wmb();
 	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 			      (atomic_t *)(&sem->count)) < 0)
 		rwsem_wake(sem);
@@ -113,7 +105,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 	if (tmp < 0)
 		rwsem_downgrade_wake(sem);
@@ -124,7 +115,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
  */
 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 {
-	smp_mb();
 	return atomic_add_return(delta, (atomic_t *)(&sem->count));
 }
 
-- 
2.8.0.rc3

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#1377809 — [tip:locking/rwsem] locking/rwsem: Drop explicit memory barriers

Fromtip-bot for Michal Hocko <tipbot@zytor.com>
Date2016-04-13 13:40 +0200
Subject[tip:locking/rwsem] locking/rwsem: Drop explicit memory barriers
Message-ID<rnrjm-x5-79@gated-at.bofh.it>
In reply to#1373479
Commit-ID:  2e927c6422fea5ce36b24b00c2c84f2e9ead31b6
Gitweb:     http://git.kernel.org/tip/2e927c6422fea5ce36b24b00c2c84f2e9ead31b6
Author:     Michal Hocko <mhocko@suse.com>
AuthorDate: Thu, 7 Apr 2016 17:12:22 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 13 Apr 2016 10:42:18 +0200

locking/rwsem: Drop explicit memory barriers

sh and xtensa seem to be the only architectures which use explicit
memory barriers for rw_semaphore operations even though they are not
really needed because there is the full memory barrier is always implied
by atomic_{inc,dec,add,sub}_return() resp. cmpxchg(). Remove them.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Signed-off-by: Jason Low <jason.low2@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-alpha@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: linux-xtensa@linux-xtensa.org
Cc: sparclinux@vger.kernel.org
Link: http://lkml.kernel.org/r/1460041951-22347-3-git-send-email-mhocko@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/sh/include/asm/rwsem.h     | 14 ++------------
 arch/xtensa/include/asm/rwsem.h | 14 ++------------
 2 files changed, 4 insertions(+), 24 deletions(-)

diff --git a/arch/sh/include/asm/rwsem.h b/arch/sh/include/asm/rwsem.h
index a5104be..f6c951c 100644
--- a/arch/sh/include/asm/rwsem.h
+++ b/arch/sh/include/asm/rwsem.h
@@ -24,9 +24,7 @@
  */
 static inline void __down_read(struct rw_semaphore *sem)
 {
-	if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
-		smp_wmb();
-	else
+	if (atomic_inc_return((atomic_t *)(&sem->count)) <= 0)
 		rwsem_down_read_failed(sem);
 }
 
@@ -37,7 +35,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 	while ((tmp = sem->count) >= 0) {
 		if (tmp == cmpxchg(&sem->count, tmp,
 				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			smp_wmb();
 			return 1;
 		}
 	}
@@ -53,9 +50,7 @@ static inline void __down_write(struct rw_semaphore *sem)
 
 	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 				(atomic_t *)(&sem->count));
-	if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
-		smp_wmb();
-	else
+	if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
 		rwsem_down_write_failed(sem);
 }
 
@@ -65,7 +60,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
 
 	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 		      RWSEM_ACTIVE_WRITE_BIAS);
-	smp_wmb();
 	return tmp == RWSEM_UNLOCKED_VALUE;
 }
 
@@ -76,7 +70,6 @@ static inline void __up_read(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_dec_return((atomic_t *)(&sem->count));
 	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
 		rwsem_wake(sem);
@@ -87,7 +80,6 @@ static inline void __up_read(struct rw_semaphore *sem)
  */
 static inline void __up_write(struct rw_semaphore *sem)
 {
-	smp_wmb();
 	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 			      (atomic_t *)(&sem->count)) < 0)
 		rwsem_wake(sem);
@@ -108,7 +100,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 	if (tmp < 0)
 		rwsem_downgrade_wake(sem);
@@ -119,7 +110,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
  */
 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 {
-	smp_mb();
 	return atomic_add_return(delta, (atomic_t *)(&sem->count));
 }
 
diff --git a/arch/xtensa/include/asm/rwsem.h b/arch/xtensa/include/asm/rwsem.h
index 249619e..593483f 100644
--- a/arch/xtensa/include/asm/rwsem.h
+++ b/arch/xtensa/include/asm/rwsem.h
@@ -29,9 +29,7 @@
  */
 static inline void __down_read(struct rw_semaphore *sem)
 {
-	if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
-		smp_wmb();
-	else
+	if (atomic_add_return(1,(atomic_t *)(&sem->count)) <= 0)
 		rwsem_down_read_failed(sem);
 }
 
@@ -42,7 +40,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 	while ((tmp = sem->count) >= 0) {
 		if (tmp == cmpxchg(&sem->count, tmp,
 				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			smp_wmb();
 			return 1;
 		}
 	}
@@ -58,9 +55,7 @@ static inline void __down_write(struct rw_semaphore *sem)
 
 	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 				(atomic_t *)(&sem->count));
-	if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
-		smp_wmb();
-	else
+	if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
 		rwsem_down_write_failed(sem);
 }
 
@@ -70,7 +65,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
 
 	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 		      RWSEM_ACTIVE_WRITE_BIAS);
-	smp_wmb();
 	return tmp == RWSEM_UNLOCKED_VALUE;
 }
 
@@ -81,7 +75,6 @@ static inline void __up_read(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
 	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
 		rwsem_wake(sem);
@@ -92,7 +85,6 @@ static inline void __up_read(struct rw_semaphore *sem)
  */
 static inline void __up_write(struct rw_semaphore *sem)
 {
-	smp_wmb();
 	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 			      (atomic_t *)(&sem->count)) < 0)
 		rwsem_wake(sem);
@@ -113,7 +105,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 	if (tmp < 0)
 		rwsem_downgrade_wake(sem);
@@ -124,7 +115,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
  */
 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 {
-	smp_mb();
 	return atomic_add_return(delta, (atomic_t *)(&sem->count));
 }

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#1373480 — [PATCH 06/11] locking, rwsem: introduce basis for down_write_killable

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-07 17:30 +0200
Subject[PATCH 06/11] locking, rwsem: introduce basis for down_write_killable
Message-ID<rlk2B-5YE-1@gated-at.bofh.it>
In reply to#1373475
From: Michal Hocko <mhocko@suse.com>

Introduce a generic implementation necessary for down_write_killable.
This is a trivial extension of the already existing down_write call
which can be interrupted by SIGKILL.  This patch doesn't provide
down_write_killable yet because arches have to provide the necessary
pieces before.

rwsem_down_write_failed which is a generic slow path for the
write lock is extended to take a task state and renamed to
__rwsem_down_write_failed_common. The return value is either a valid
semaphore pointer or ERR_PTR(-EINTR).

rwsem_down_write_failed_killable is exported as a new way to wait for
the lock and be killable.

For rwsem-spinlock implementation the current __down_write it updated
in a similar way as __rwsem_down_write_failed_common except it doesn't
need new exports just visible __down_write_killable.

Architectures which are not using the generic rwsem implementation are
supposed to provide their __down_write_killable implementation and
use rwsem_down_write_failed_killable for the slow path.

[dave@stgolabs.net - rename __rwsem_down_write_failed_state to
 __rwsem_down_write_failed_common]
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 include/asm-generic/rwsem.h     | 12 ++++++++++++
 include/linux/rwsem-spinlock.h  |  1 +
 include/linux/rwsem.h           |  2 ++
 kernel/locking/rwsem-spinlock.c | 22 ++++++++++++++++++++--
 kernel/locking/rwsem-xadd.c     | 31 +++++++++++++++++++++++++------
 5 files changed, 60 insertions(+), 8 deletions(-)

diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
index b8d8a6cf4ca8..3fc94a046bf5 100644
--- a/include/asm-generic/rwsem.h
+++ b/include/asm-generic/rwsem.h
@@ -63,6 +63,18 @@ static inline void __down_write(struct rw_semaphore *sem)
 		rwsem_down_write_failed(sem);
 }
 
+static inline int __down_write_killable(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
+				     (atomic_long_t *)&sem->count);
+	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
+		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
+			return -EINTR;
+	return 0;
+}
+
 static inline int __down_write_trylock(struct rw_semaphore *sem)
 {
 	long tmp;
diff --git a/include/linux/rwsem-spinlock.h b/include/linux/rwsem-spinlock.h
index a733a5467e6c..ae0528b834cd 100644
--- a/include/linux/rwsem-spinlock.h
+++ b/include/linux/rwsem-spinlock.h
@@ -34,6 +34,7 @@ struct rw_semaphore {
 extern void __down_read(struct rw_semaphore *sem);
 extern int __down_read_trylock(struct rw_semaphore *sem);
 extern void __down_write(struct rw_semaphore *sem);
+extern int __must_check __down_write_killable(struct rw_semaphore *sem);
 extern int __down_write_trylock(struct rw_semaphore *sem);
 extern void __up_read(struct rw_semaphore *sem);
 extern void __up_write(struct rw_semaphore *sem);
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 8f498cdde280..7d7ae029dac5 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -14,6 +14,7 @@
 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/atomic.h>
+#include <linux/err.h>
 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 #include <linux/osq_lock.h>
 #endif
@@ -43,6 +44,7 @@ struct rw_semaphore {
 
 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
+extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
 
diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c
index bab26104a5d0..1591f6b3539f 100644
--- a/kernel/locking/rwsem-spinlock.c
+++ b/kernel/locking/rwsem-spinlock.c
@@ -191,11 +191,12 @@ int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * get a write lock on the semaphore
  */
-void __sched __down_write(struct rw_semaphore *sem)
+int __sched __down_write_common(struct rw_semaphore *sem, int state)
 {
 	struct rwsem_waiter waiter;
 	struct task_struct *tsk;
 	unsigned long flags;
+	int ret = 0;
 
 	raw_spin_lock_irqsave(&sem->wait_lock, flags);
 
@@ -215,16 +216,33 @@ void __sched __down_write(struct rw_semaphore *sem)
 		 */
 		if (sem->count == 0)
 			break;
-		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+		if (signal_pending_state(state, current)) {
+			ret = -EINTR;
+			goto out;
+		}
+		set_task_state(tsk, state);
 		raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 		schedule();
 		raw_spin_lock_irqsave(&sem->wait_lock, flags);
 	}
 	/* got the lock */
 	sem->count = -1;
+out:
 	list_del(&waiter.list);
 
 	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+	return ret;
+}
+
+void __sched __down_write(struct rw_semaphore *sem)
+{
+	__down_write_common(sem, TASK_UNINTERRUPTIBLE);
+}
+
+int __sched __down_write_killable(struct rw_semaphore *sem)
+{
+	return __down_write_common(sem, TASK_KILLABLE);
 }
 
 /*
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index a4d4de05b2d1..df4dcb883b50 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -433,12 +433,13 @@ static inline bool rwsem_has_spinner(struct rw_semaphore *sem)
 /*
  * Wait until we successfully acquire the write lock
  */
-__visible
-struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
+static inline struct rw_semaphore *
+__rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
 {
 	long count;
 	bool waiting = true; /* any queued threads before us */
 	struct rwsem_waiter waiter;
+	struct rw_semaphore *ret = sem;
 
 	/* undo write bias from down_write operation, stop active locking */
 	count = rwsem_atomic_update(-RWSEM_ACTIVE_WRITE_BIAS, sem);
@@ -478,7 +479,7 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
 		count = rwsem_atomic_update(RWSEM_WAITING_BIAS, sem);
 
 	/* wait until we successfully acquire the lock */
-	set_current_state(TASK_UNINTERRUPTIBLE);
+	set_current_state(state);
 	while (true) {
 		if (rwsem_try_write_lock(count, sem))
 			break;
@@ -486,21 +487,39 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
 
 		/* Block until there are no active lockers. */
 		do {
+			if (signal_pending_state(state, current)) {
+				raw_spin_lock_irq(&sem->wait_lock);
+				ret = ERR_PTR(-EINTR);
+				goto out;
+			}
 			schedule();
-			set_current_state(TASK_UNINTERRUPTIBLE);
+			set_current_state(state);
 		} while ((count = sem->count) & RWSEM_ACTIVE_MASK);
 
 		raw_spin_lock_irq(&sem->wait_lock);
 	}
+out:
 	__set_current_state(TASK_RUNNING);
-
 	list_del(&waiter.list);
 	raw_spin_unlock_irq(&sem->wait_lock);
 
-	return sem;
+	return ret;
+}
+
+__visible struct rw_semaphore * __sched
+rwsem_down_write_failed(struct rw_semaphore *sem)
+{
+	return __rwsem_down_write_failed_common(sem, TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(rwsem_down_write_failed);
 
+__visible struct rw_semaphore * __sched
+rwsem_down_write_failed_killable(struct rw_semaphore *sem)
+{
+	return __rwsem_down_write_failed_common(sem, TASK_KILLABLE);
+}
+EXPORT_SYMBOL(rwsem_down_write_failed_killable);
+
 /*
  * handle waking up a waiter on the semaphore
  * - up_read/up_write has decremented the active part of count if we come here
-- 
2.8.0.rc3

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#1377801 — [tip:locking/rwsem] locking/rwsem: Introduce basis for down_write_killable()

Fromtip-bot for Michal Hocko <tipbot@zytor.com>
Date2016-04-13 13:40 +0200
Subject[tip:locking/rwsem] locking/rwsem: Introduce basis for down_write_killable()
Message-ID<rnrjl-x5-49@gated-at.bofh.it>
In reply to#1373480
Commit-ID:  d47996082f52baa0ca8b48d26b3cbef5ede70a73
Gitweb:     http://git.kernel.org/tip/d47996082f52baa0ca8b48d26b3cbef5ede70a73
Author:     Michal Hocko <mhocko@suse.com>
AuthorDate: Thu, 7 Apr 2016 17:12:26 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 13 Apr 2016 10:42:20 +0200

locking/rwsem: Introduce basis for down_write_killable()

Introduce a generic implementation necessary for down_write_killable().

This is a trivial extension of the already existing down_write() call
which can be interrupted by SIGKILL.  This patch doesn't provide
down_write_killable() yet because arches have to provide the necessary
pieces before.

rwsem_down_write_failed() which is a generic slow path for the
write lock is extended to take a task state and renamed to
__rwsem_down_write_failed_common(). The return value is either a valid
semaphore pointer or ERR_PTR(-EINTR).

rwsem_down_write_failed_killable() is exported as a new way to wait for
the lock and be killable.

For rwsem-spinlock implementation the current __down_write() it updated
in a similar way as __rwsem_down_write_failed_common() except it doesn't
need new exports just visible __down_write_killable().

Architectures which are not using the generic rwsem implementation are
supposed to provide their __down_write_killable() implementation and
use rwsem_down_write_failed_killable() for the slow path.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Signed-off-by: Jason Low <jason.low2@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-alpha@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: linux-xtensa@linux-xtensa.org
Cc: sparclinux@vger.kernel.org
Link: http://lkml.kernel.org/r/1460041951-22347-7-git-send-email-mhocko@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/asm-generic/rwsem.h     | 12 ++++++++++++
 include/linux/rwsem-spinlock.h  |  1 +
 include/linux/rwsem.h           |  2 ++
 kernel/locking/rwsem-spinlock.c | 22 ++++++++++++++++++++--
 kernel/locking/rwsem-xadd.c     | 31 +++++++++++++++++++++++++------
 5 files changed, 60 insertions(+), 8 deletions(-)

diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
index b8d8a6c..3fc94a0 100644
--- a/include/asm-generic/rwsem.h
+++ b/include/asm-generic/rwsem.h
@@ -63,6 +63,18 @@ static inline void __down_write(struct rw_semaphore *sem)
 		rwsem_down_write_failed(sem);
 }
 
+static inline int __down_write_killable(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
+				     (atomic_long_t *)&sem->count);
+	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
+		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
+			return -EINTR;
+	return 0;
+}
+
 static inline int __down_write_trylock(struct rw_semaphore *sem)
 {
 	long tmp;
diff --git a/include/linux/rwsem-spinlock.h b/include/linux/rwsem-spinlock.h
index a733a54..ae0528b 100644
--- a/include/linux/rwsem-spinlock.h
+++ b/include/linux/rwsem-spinlock.h
@@ -34,6 +34,7 @@ struct rw_semaphore {
 extern void __down_read(struct rw_semaphore *sem);
 extern int __down_read_trylock(struct rw_semaphore *sem);
 extern void __down_write(struct rw_semaphore *sem);
+extern int __must_check __down_write_killable(struct rw_semaphore *sem);
 extern int __down_write_trylock(struct rw_semaphore *sem);
 extern void __up_read(struct rw_semaphore *sem);
 extern void __up_write(struct rw_semaphore *sem);
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 8f498cd..7d7ae02 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -14,6 +14,7 @@
 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/atomic.h>
+#include <linux/err.h>
 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 #include <linux/osq_lock.h>
 #endif
@@ -43,6 +44,7 @@ struct rw_semaphore {
 
 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
+extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
 
diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c
index bab2610..1591f6b 100644
--- a/kernel/locking/rwsem-spinlock.c
+++ b/kernel/locking/rwsem-spinlock.c
@@ -191,11 +191,12 @@ int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * get a write lock on the semaphore
  */
-void __sched __down_write(struct rw_semaphore *sem)
+int __sched __down_write_common(struct rw_semaphore *sem, int state)
 {
 	struct rwsem_waiter waiter;
 	struct task_struct *tsk;
 	unsigned long flags;
+	int ret = 0;
 
 	raw_spin_lock_irqsave(&sem->wait_lock, flags);
 
@@ -215,16 +216,33 @@ void __sched __down_write(struct rw_semaphore *sem)
 		 */
 		if (sem->count == 0)
 			break;
-		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+		if (signal_pending_state(state, current)) {
+			ret = -EINTR;
+			goto out;
+		}
+		set_task_state(tsk, state);
 		raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 		schedule();
 		raw_spin_lock_irqsave(&sem->wait_lock, flags);
 	}
 	/* got the lock */
 	sem->count = -1;
+out:
 	list_del(&waiter.list);
 
 	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+	return ret;
+}
+
+void __sched __down_write(struct rw_semaphore *sem)
+{
+	__down_write_common(sem, TASK_UNINTERRUPTIBLE);
+}
+
+int __sched __down_write_killable(struct rw_semaphore *sem)
+{
+	return __down_write_common(sem, TASK_KILLABLE);
 }
 
 /*
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index a4d4de0..df4dcb8 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -433,12 +433,13 @@ static inline bool rwsem_has_spinner(struct rw_semaphore *sem)
 /*
  * Wait until we successfully acquire the write lock
  */
-__visible
-struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
+static inline struct rw_semaphore *
+__rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
 {
 	long count;
 	bool waiting = true; /* any queued threads before us */
 	struct rwsem_waiter waiter;
+	struct rw_semaphore *ret = sem;
 
 	/* undo write bias from down_write operation, stop active locking */
 	count = rwsem_atomic_update(-RWSEM_ACTIVE_WRITE_BIAS, sem);
@@ -478,7 +479,7 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
 		count = rwsem_atomic_update(RWSEM_WAITING_BIAS, sem);
 
 	/* wait until we successfully acquire the lock */
-	set_current_state(TASK_UNINTERRUPTIBLE);
+	set_current_state(state);
 	while (true) {
 		if (rwsem_try_write_lock(count, sem))
 			break;
@@ -486,21 +487,39 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
 
 		/* Block until there are no active lockers. */
 		do {
+			if (signal_pending_state(state, current)) {
+				raw_spin_lock_irq(&sem->wait_lock);
+				ret = ERR_PTR(-EINTR);
+				goto out;
+			}
 			schedule();
-			set_current_state(TASK_UNINTERRUPTIBLE);
+			set_current_state(state);
 		} while ((count = sem->count) & RWSEM_ACTIVE_MASK);
 
 		raw_spin_lock_irq(&sem->wait_lock);
 	}
+out:
 	__set_current_state(TASK_RUNNING);
-
 	list_del(&waiter.list);
 	raw_spin_unlock_irq(&sem->wait_lock);
 
-	return sem;
+	return ret;
+}
+
+__visible struct rw_semaphore * __sched
+rwsem_down_write_failed(struct rw_semaphore *sem)
+{
+	return __rwsem_down_write_failed_common(sem, TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(rwsem_down_write_failed);
 
+__visible struct rw_semaphore * __sched
+rwsem_down_write_failed_killable(struct rw_semaphore *sem)
+{
+	return __rwsem_down_write_failed_common(sem, TASK_KILLABLE);
+}
+EXPORT_SYMBOL(rwsem_down_write_failed_killable);
+
 /*
  * handle waking up a waiter on the semaphore
  * - up_read/up_write has decremented the active part of count if we come here

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#1373483 — [PATCH 11/11] locking, rwsem: provide down_write_killable

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-07 17:30 +0200
Subject[PATCH 11/11] locking, rwsem: provide down_write_killable
Message-ID<rlk2C-5YE-11@gated-at.bofh.it>
In reply to#1373475
From: Michal Hocko <mhocko@suse.com>

Now that all the architectures implement the necessary glue code
we can introduce down_write_killable. The only difference wrt. regular
down_write is that the slow path waits in TASK_KILLABLE state and the
interruption by the fatal signal is reported as -EINTR to the caller.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 include/linux/lockdep.h | 15 +++++++++++++++
 include/linux/rwsem.h   |  1 +
 kernel/locking/rwsem.c  | 19 +++++++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 4dca42fd32f5..13a80779b6da 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -446,6 +446,18 @@ do {								\
 	lock_acquired(&(_lock)->dep_map, _RET_IP_);			\
 } while (0)
 
+#define LOCK_CONTENDED_RETURN(_lock, try, lock)			\
+({								\
+	int ____err = 0;					\
+	if (!try(_lock)) {					\
+		lock_contended(&(_lock)->dep_map, _RET_IP_);	\
+		____err = lock(_lock);				\
+	}							\
+	if (!____err)						\
+		lock_acquired(&(_lock)->dep_map, _RET_IP_);	\
+	____err;						\
+})
+
 #else /* CONFIG_LOCK_STAT */
 
 #define lock_contended(lockdep_map, ip) do {} while (0)
@@ -454,6 +466,9 @@ do {								\
 #define LOCK_CONTENDED(_lock, try, lock) \
 	lock(_lock)
 
+#define LOCK_CONTENDED_RETURN(_lock, try, lock) \
+	lock(_lock)
+
 #endif /* CONFIG_LOCK_STAT */
 
 #ifdef CONFIG_LOCKDEP
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 7d7ae029dac5..d1c12d160ace 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -118,6 +118,7 @@ extern int down_read_trylock(struct rw_semaphore *sem);
  * lock for writing
  */
 extern void down_write(struct rw_semaphore *sem);
+extern int __must_check down_write_killable(struct rw_semaphore *sem);
 
 /*
  * trylock for writing -- returns 1 if successful, 0 if contention
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 205be0ce34de..c817216c1615 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -55,6 +55,25 @@ void __sched down_write(struct rw_semaphore *sem)
 EXPORT_SYMBOL(down_write);
 
 /*
+ * lock for writing
+ */
+int __sched down_write_killable(struct rw_semaphore *sem)
+{
+	might_sleep();
+	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
+
+	if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock, __down_write_killable)) {
+		rwsem_release(&sem->dep_map, 1, _RET_IP_);
+		return -EINTR;
+	}
+
+	rwsem_set_owner(sem);
+	return 0;
+}
+
+EXPORT_SYMBOL(down_write_killable);
+
+/*
  * trylock for writing -- returns 1 if successful, 0 if contention
  */
 int down_write_trylock(struct rw_semaphore *sem)
-- 
2.8.0.rc3

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#1373484 — [PATCH 08/11] ia64, rwsem: provide __down_write_killable

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-07 17:30 +0200
Subject[PATCH 08/11] ia64, rwsem: provide __down_write_killable
Message-ID<rlk2C-5YE-19@gated-at.bofh.it>
In reply to#1373475
From: Michal Hocko <mhocko@suse.com>

Introduce ___down_write for the fast path and reuse it for __down_write
resp. __down_write_killable each using the respective generic slow path
(rwsem_down_write_failed resp. rwsem_down_write_failed_killable).

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 arch/ia64/include/asm/rwsem.h | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/arch/ia64/include/asm/rwsem.h b/arch/ia64/include/asm/rwsem.h
index 3027e7516d85..5e78cb40d9df 100644
--- a/arch/ia64/include/asm/rwsem.h
+++ b/arch/ia64/include/asm/rwsem.h
@@ -49,8 +49,8 @@ __down_read (struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline void
-__down_write (struct rw_semaphore *sem)
+static inline long
+___down_write (struct rw_semaphore *sem)
 {
 	long old, new;
 
@@ -59,10 +59,26 @@ __down_write (struct rw_semaphore *sem)
 		new = old + RWSEM_ACTIVE_WRITE_BIAS;
 	} while (cmpxchg_acq(&sem->count, old, new) != old);
 
-	if (old != 0)
+	return old;
+}
+
+static inline void
+__down_write (struct rw_semaphore *sem)
+{
+	if (___down_write(sem))
 		rwsem_down_write_failed(sem);
 }
 
+static inline int
+__down_write_killable (struct rw_semaphore *sem)
+{
+	if (___down_write(sem))
+		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
+			return -EINTR;
+
+	return 0;
+}
+
 /*
  * unlock after reading
  */
-- 
2.8.0.rc3

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#1373585 — Re: [PATCH 08/11] ia64, rwsem: provide __down_write_killable

FromSergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Date2016-04-07 19:30 +0200
SubjectRe: [PATCH 08/11] ia64, rwsem: provide __down_write_killable
Message-ID<rllUJ-7og-1@gated-at.bofh.it>
In reply to#1373484
Hello.

On 04/07/2016 06:12 PM, Michal Hocko wrote:

> From: Michal Hocko <mhocko@suse.com>
>
> Introduce ___down_write for the fast path and reuse it for __down_write
> resp. __down_write_killable each using the respective generic slow path
> (rwsem_down_write_failed resp. rwsem_down_write_failed_killable).
>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>   arch/ia64/include/asm/rwsem.h | 22 +++++++++++++++++++---
>   1 file changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/arch/ia64/include/asm/rwsem.h b/arch/ia64/include/asm/rwsem.h
> index 3027e7516d85..5e78cb40d9df 100644
> --- a/arch/ia64/include/asm/rwsem.h
> +++ b/arch/ia64/include/asm/rwsem.h
> @@ -49,8 +49,8 @@ __down_read (struct rw_semaphore *sem)
>   /*
>    * lock for writing
>    */
> -static inline void
> -__down_write (struct rw_semaphore *sem)
> +static inline long
> +___down_write (struct rw_semaphore *sem)
>   {
>   	long old, new;
>
> @@ -59,10 +59,26 @@ __down_write (struct rw_semaphore *sem)
>   		new = old + RWSEM_ACTIVE_WRITE_BIAS;
>   	} while (cmpxchg_acq(&sem->count, old, new) != old);
>
> -	if (old != 0)
> +	return old;
> +}
> +
> +static inline void
> +__down_write (struct rw_semaphore *sem)
> +{
> +	if (___down_write(sem))
>   		rwsem_down_write_failed(sem);
>   }
>
> +static inline int
> +__down_write_killable (struct rw_semaphore *sem)

    Looks like you haven't run this patch thru scripts/checkpatch.pl. Hint: 
space before ( isn't allowed.

[...]

MNBR, Sergei

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#1374006 — Re: [PATCH 08/11] ia64, rwsem: provide __down_write_killable

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-08 08:30 +0200
SubjectRe: [PATCH 08/11] ia64, rwsem: provide __down_write_killable
Message-ID<rly5A-86x-21@gated-at.bofh.it>
In reply to#1373585
On Thu 07-04-16 20:28:16, Sergei Shtylyov wrote:
> Hello.
> 
> On 04/07/2016 06:12 PM, Michal Hocko wrote:
> 
> >From: Michal Hocko <mhocko@suse.com>
> >
> >Introduce ___down_write for the fast path and reuse it for __down_write
> >resp. __down_write_killable each using the respective generic slow path
> >(rwsem_down_write_failed resp. rwsem_down_write_failed_killable).
> >
> >Signed-off-by: Michal Hocko <mhocko@suse.com>
> >---
> >  arch/ia64/include/asm/rwsem.h | 22 +++++++++++++++++++---
> >  1 file changed, 19 insertions(+), 3 deletions(-)
> >
> >diff --git a/arch/ia64/include/asm/rwsem.h b/arch/ia64/include/asm/rwsem.h
> >index 3027e7516d85..5e78cb40d9df 100644
> >--- a/arch/ia64/include/asm/rwsem.h
> >+++ b/arch/ia64/include/asm/rwsem.h
> >@@ -49,8 +49,8 @@ __down_read (struct rw_semaphore *sem)
> >  /*
> >   * lock for writing
> >   */
> >-static inline void
> >-__down_write (struct rw_semaphore *sem)
> >+static inline long
> >+___down_write (struct rw_semaphore *sem)
> >  {
> >  	long old, new;
> >
> >@@ -59,10 +59,26 @@ __down_write (struct rw_semaphore *sem)
> >  		new = old + RWSEM_ACTIVE_WRITE_BIAS;
> >  	} while (cmpxchg_acq(&sem->count, old, new) != old);
> >
> >-	if (old != 0)
> >+	return old;
> >+}
> >+
> >+static inline void
> >+__down_write (struct rw_semaphore *sem)
> >+{
> >+	if (___down_write(sem))
> >  		rwsem_down_write_failed(sem);
> >  }
> >
> >+static inline int
> >+__down_write_killable (struct rw_semaphore *sem)
> 
>    Looks like you haven't run this patch thru scripts/checkpatch.pl. Hint:
> space before ( isn't allowed.

I have just kept the original code styling because I didn't feel like
changing the whole file.

-- 
Michal Hocko
SUSE Labs

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#1373486 — [PATCH 03/11] xtensa, rwsem: drop superfluous arch specific implementation

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-07 17:30 +0200
Subject[PATCH 03/11] xtensa, rwsem: drop superfluous arch specific implementation
Message-ID<rlk2C-5YE-17@gated-at.bofh.it>
In reply to#1373475
From: Michal Hocko <mhocko@suse.com>

since "locking, rwsem: drop explicit memory barriers" the arch specific
code is basically same as the the generic one so we can drop the
superfluous code.

Suggested-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 arch/xtensa/include/asm/Kbuild  |   1 +
 arch/xtensa/include/asm/rwsem.h | 121 ----------------------------------------
 2 files changed, 1 insertion(+), 121 deletions(-)
 delete mode 100644 arch/xtensa/include/asm/rwsem.h

diff --git a/arch/xtensa/include/asm/Kbuild b/arch/xtensa/include/asm/Kbuild
index b56855a1382a..28cf4c5d65ef 100644
--- a/arch/xtensa/include/asm/Kbuild
+++ b/arch/xtensa/include/asm/Kbuild
@@ -22,6 +22,7 @@ generic-y += mm-arch-hooks.h
 generic-y += percpu.h
 generic-y += preempt.h
 generic-y += resource.h
+generic-y += rwsem.h
 generic-y += sections.h
 generic-y += siginfo.h
 generic-y += statfs.h
diff --git a/arch/xtensa/include/asm/rwsem.h b/arch/xtensa/include/asm/rwsem.h
deleted file mode 100644
index 593483f6e1ff..000000000000
--- a/arch/xtensa/include/asm/rwsem.h
+++ /dev/null
@@ -1,121 +0,0 @@
-/*
- * include/asm-xtensa/rwsem.h
- *
- * This file is subject to the terms and conditions of the GNU General Public
- * License.  See the file "COPYING" in the main directory of this archive
- * for more details.
- *
- * Largely copied from include/asm-ppc/rwsem.h
- *
- * Copyright (C) 2001 - 2005 Tensilica Inc.
- */
-
-#ifndef _XTENSA_RWSEM_H
-#define _XTENSA_RWSEM_H
-
-#ifndef _LINUX_RWSEM_H
-#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
-#endif
-
-#define RWSEM_UNLOCKED_VALUE		0x00000000
-#define RWSEM_ACTIVE_BIAS		0x00000001
-#define RWSEM_ACTIVE_MASK		0x0000ffff
-#define RWSEM_WAITING_BIAS		(-0x00010000)
-#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
-#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
-
-/*
- * lock for reading
- */
-static inline void __down_read(struct rw_semaphore *sem)
-{
-	if (atomic_add_return(1,(atomic_t *)(&sem->count)) <= 0)
-		rwsem_down_read_failed(sem);
-}
-
-static inline int __down_read_trylock(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	while ((tmp = sem->count) >= 0) {
-		if (tmp == cmpxchg(&sem->count, tmp,
-				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			return 1;
-		}
-	}
-	return 0;
-}
-
-/*
- * lock for writing
- */
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
-				(atomic_t *)(&sem->count));
-	if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
-		rwsem_down_write_failed(sem);
-}
-
-static inline int __down_write_trylock(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
-		      RWSEM_ACTIVE_WRITE_BIAS);
-	return tmp == RWSEM_UNLOCKED_VALUE;
-}
-
-/*
- * unlock after reading
- */
-static inline void __up_read(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
-	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
-		rwsem_wake(sem);
-}
-
-/*
- * unlock after writing
- */
-static inline void __up_write(struct rw_semaphore *sem)
-{
-	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
-			      (atomic_t *)(&sem->count)) < 0)
-		rwsem_wake(sem);
-}
-
-/*
- * implement atomic add functionality
- */
-static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
-{
-	atomic_add(delta, (atomic_t *)(&sem->count));
-}
-
-/*
- * downgrade write lock to read lock
- */
-static inline void __downgrade_write(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
-	if (tmp < 0)
-		rwsem_downgrade_wake(sem);
-}
-
-/*
- * implement exchange and add functionality
- */
-static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
-{
-	return atomic_add_return(delta, (atomic_t *)(&sem->count));
-}
-
-#endif	/* _XTENSA_RWSEM_H */
-- 
2.8.0.rc3

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#1377807 — [tip:locking/rwsem] locking/rwsem, xtensa: Drop superfluous arch specific implementation

Fromtip-bot for Michal Hocko <tipbot@zytor.com>
Date2016-04-13 13:40 +0200
Subject[tip:locking/rwsem] locking/rwsem, xtensa: Drop superfluous arch specific implementation
Message-ID<rnrjm-x5-67@gated-at.bofh.it>
In reply to#1373486
Commit-ID:  3aa2591dc2ea292d068dc3a263f1976806c2c281
Gitweb:     http://git.kernel.org/tip/3aa2591dc2ea292d068dc3a263f1976806c2c281
Author:     Michal Hocko <mhocko@suse.com>
AuthorDate: Thu, 7 Apr 2016 17:12:23 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 13 Apr 2016 10:42:18 +0200

locking/rwsem, xtensa: Drop superfluous arch specific implementation

Since "locking, rwsem: drop explicit memory barriers" the arch specific
code is basically same as the the generic one so we can drop the
superfluous code.

Suggested-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Signed-off-by: Jason Low <jason.low2@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-alpha@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: linux-xtensa@linux-xtensa.org
Cc: sparclinux@vger.kernel.org
Link: http://lkml.kernel.org/r/1460041951-22347-4-git-send-email-mhocko@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/xtensa/include/asm/Kbuild  |   1 +
 arch/xtensa/include/asm/rwsem.h | 121 ----------------------------------------
 2 files changed, 1 insertion(+), 121 deletions(-)

diff --git a/arch/xtensa/include/asm/Kbuild b/arch/xtensa/include/asm/Kbuild
index b56855a..28cf4c5 100644
--- a/arch/xtensa/include/asm/Kbuild
+++ b/arch/xtensa/include/asm/Kbuild
@@ -22,6 +22,7 @@ generic-y += mm-arch-hooks.h
 generic-y += percpu.h
 generic-y += preempt.h
 generic-y += resource.h
+generic-y += rwsem.h
 generic-y += sections.h
 generic-y += siginfo.h
 generic-y += statfs.h
diff --git a/arch/xtensa/include/asm/rwsem.h b/arch/xtensa/include/asm/rwsem.h
deleted file mode 100644
index 593483f..0000000
--- a/arch/xtensa/include/asm/rwsem.h
+++ /dev/null
@@ -1,121 +0,0 @@
-/*
- * include/asm-xtensa/rwsem.h
- *
- * This file is subject to the terms and conditions of the GNU General Public
- * License.  See the file "COPYING" in the main directory of this archive
- * for more details.
- *
- * Largely copied from include/asm-ppc/rwsem.h
- *
- * Copyright (C) 2001 - 2005 Tensilica Inc.
- */
-
-#ifndef _XTENSA_RWSEM_H
-#define _XTENSA_RWSEM_H
-
-#ifndef _LINUX_RWSEM_H
-#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
-#endif
-
-#define RWSEM_UNLOCKED_VALUE		0x00000000
-#define RWSEM_ACTIVE_BIAS		0x00000001
-#define RWSEM_ACTIVE_MASK		0x0000ffff
-#define RWSEM_WAITING_BIAS		(-0x00010000)
-#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
-#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
-
-/*
- * lock for reading
- */
-static inline void __down_read(struct rw_semaphore *sem)
-{
-	if (atomic_add_return(1,(atomic_t *)(&sem->count)) <= 0)
-		rwsem_down_read_failed(sem);
-}
-
-static inline int __down_read_trylock(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	while ((tmp = sem->count) >= 0) {
-		if (tmp == cmpxchg(&sem->count, tmp,
-				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			return 1;
-		}
-	}
-	return 0;
-}
-
-/*
- * lock for writing
- */
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
-				(atomic_t *)(&sem->count));
-	if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
-		rwsem_down_write_failed(sem);
-}
-
-static inline int __down_write_trylock(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
-		      RWSEM_ACTIVE_WRITE_BIAS);
-	return tmp == RWSEM_UNLOCKED_VALUE;
-}
-
-/*
- * unlock after reading
- */
-static inline void __up_read(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
-	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
-		rwsem_wake(sem);
-}
-
-/*
- * unlock after writing
- */
-static inline void __up_write(struct rw_semaphore *sem)
-{
-	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
-			      (atomic_t *)(&sem->count)) < 0)
-		rwsem_wake(sem);
-}
-
-/*
- * implement atomic add functionality
- */
-static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
-{
-	atomic_add(delta, (atomic_t *)(&sem->count));
-}
-
-/*
- * downgrade write lock to read lock
- */
-static inline void __downgrade_write(struct rw_semaphore *sem)
-{
-	int tmp;
-
-	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
-	if (tmp < 0)
-		rwsem_downgrade_wake(sem);
-}
-
-/*
- * implement exchange and add functionality
- */
-static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
-{
-	return atomic_add_return(delta, (atomic_t *)(&sem->count));
-}
-
-#endif	/* _XTENSA_RWSEM_H */

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#1376603

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-12 11:40 +0200
Message-ID<rn2XF-4YH-51@gated-at.bofh.it>
In reply to#1373475
Hi Ingo, Peter,
do you plan to pull this into tip/locking or are you waiting for some
more feedback or things to resolve?

Thanks!
-- 
Michal Hocko
SUSE Labs

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#1376956

FromPeter Zijlstra <peterz@infradead.org>
Date2016-04-12 17:50 +0200
Message-ID<rn8JI-1i4-37@gated-at.bofh.it>
In reply to#1376603
On Tue, Apr 12, 2016 at 11:37:08AM +0200, Michal Hocko wrote:
> Hi Ingo, Peter,
> do you plan to pull this into tip/locking or are you waiting for some
> more feedback or things to resolve?

I am planning to take it; but I'm traveling this week.

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#1377079

FromMichal Hocko <mhocko@kernel.org>
Date2016-04-12 20:10 +0200
Message-ID<rnaVe-3iR-31@gated-at.bofh.it>
In reply to#1376956
On Tue 12-04-16 17:40:04, Peter Zijlstra wrote:
> On Tue, Apr 12, 2016 at 11:37:08AM +0200, Michal Hocko wrote:
> > Hi Ingo, Peter,
> > do you plan to pull this into tip/locking or are you waiting for some
> > more feedback or things to resolve?
> 
> I am planning to take it; but I'm traveling this week.

OK, thanks!

-- 
Michal Hocko
SUSE Labs

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