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[tip:core/rcu] fs/writeback, rcu: Don't use list_entry_rcu() for pointer offsetting in bdi_split_work_to_wbs()

From tip-bot for Tejun Heo <tipbot@zytor.com>
Newsgroups linux.kernel
Subject [tip:core/rcu] fs/writeback, rcu: Don't use list_entry_rcu() for pointer offsetting in bdi_split_work_to_wbs()
Date 2015-10-28 22:00 +0100
Message-ID <qoFZ7-7Bh-11@gated-at.bofh.it> (permalink)
References <qo4PT-18r-9@gated-at.bofh.it>
Organization linux.* mail to news gateway

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Commit-ID:  b33e18f61bd18227a456016a77b1a968f5bc1d65
Gitweb:     http://git.kernel.org/tip/b33e18f61bd18227a456016a77b1a968f5bc1d65
Author:     Tejun Heo <tj@kernel.org>
AuthorDate: Tue, 27 Oct 2015 14:19:39 +0900
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 28 Oct 2015 13:17:30 +0100

fs/writeback, rcu: Don't use list_entry_rcu() for pointer offsetting in bdi_split_work_to_wbs()

bdi_split_work_to_wbs() uses list_for_each_entry_rcu_continue()
to walk @bdi->wb_list.  To set up the initial iteration
condition, it uses list_entry_rcu() to calculate the entry
pointer corresponding to the list head; however, this isn't an
actual RCU dereference and using list_entry_rcu() for it ended
up breaking a proposed list_entry_rcu() change because it was
feeding an non-lvalue pointer into the macro.

Don't use the RCU variant for simple pointer offsetting.  Use
list_entry() instead.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Patrick Marlier <patrick.marlier@gmail.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: pranith kumar <bobby.prani@gmail.com>
Link: http://lkml.kernel.org/r/20151027051939.GA19355@mtj.duckdns.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 fs/fs-writeback.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 29e4599..7378169 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -779,8 +779,8 @@ static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
 				  bool skip_if_busy)
 {
 	struct bdi_writeback *last_wb = NULL;
-	struct bdi_writeback *wb = list_entry_rcu(&bdi->wb_list,
-						struct bdi_writeback, bdi_node);
+	struct bdi_writeback *wb = list_entry(&bdi->wb_list,
+					      struct bdi_writeback, bdi_node);
 
 	might_sleep();
 restart:
--
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Thread

Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use  lockless_dereference() Ingo Molnar <mingo@kernel.org> - 2015-10-26 09:50 +0100
  Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use  lockless_dereference() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-26 16:00 +0100
    Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use  lockless_dereference() Ingo Molnar <mingo@kernel.org> - 2015-10-26 19:10 +0100
    Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use lockless_dereference() Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-27 04:40 +0100
      Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use  lockless_dereference() Tejun Heo <tj@kernel.org> - 2015-10-27 06:20 +0100
        Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use  lockless_dereference() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-27 06:40 +0100
        Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use  lockless_dereference() Ingo Molnar <mingo@kernel.org> - 2015-10-28 09:40 +0100
          Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use  lockless_dereference() Patrick Marlier <patrick.marlier@gmail.com> - 2015-10-28 21:40 +0100
            Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use  lockless_dereference() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-29 01:10 +0100
              Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use  lockless_dereference() Tejun Heo <tj@kernel.org> - 2015-10-29 03:20 +0100
        [tip:core/rcu] fs/writeback, rcu: Don't use list_entry_rcu()   for pointer offsetting in bdi_split_work_to_wbs() tip-bot for Tejun Heo <tipbot@zytor.com> - 2015-10-28 22:00 +0100
      Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use  lockless_dereference() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-27 06:40 +0100

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