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[PATCH-tip v5 05/21] futex: Add helpers to get & cmpxchg futex value without lock

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Two new helper functions cmpxchg_futex_value() and get_futex_value()
are added to access and change the futex value without the hash
bucket lock.  As a result, page fault is enabled and the page will
be faulted in if not present yet.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/futex.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index b21c6a0..203a388 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -805,6 +805,21 @@ static int get_futex_value_locked(u32 *dest, u32 __user *from)
 	return ret ? -EFAULT : 0;
 }
 
+/*
+ * The equivalents of the above cmpxchg_futex_value_locked() and
+ * get_futex_value_locked which are called without the hash bucket lock
+ * and so can have page fault enabled.
+ */
+static inline int cmpxchg_futex_value(u32 *curval, u32 __user *uaddr,
+				      u32 uval, u32 newval)
+{
+	return futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
+}
+
+static inline int get_futex_value(u32 *dest, u32 __user *from)
+{
+	return __get_user(*dest, from);
+}
 
 /*
  * PI code:
-- 
1.8.3.1

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[PATCH-tip v5 00/21] futex: Introducing throughput-optimized (TP) futexes Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100
  [PATCH-tip v5 20/21] sched, TP-futex: Make wake_up_q() return wakeup count Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100
  [PATCH-tip v5 21/21] futex: Dump internal futex state via debugfs Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100
  [PATCH-tip v5 17/21] TP-futex: Group readers together in wait queue Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100
    Re: [PATCH-tip v5 17/21] TP-futex: Group readers together in wait queue valdis.kletnieks@vt.edu - 2017-02-03 19:30 +0100
      Re: [PATCH-tip v5 17/21] TP-futex: Group readers together in wait  queue Waiman Long <longman@redhat.com> - 2017-02-03 19:50 +0100
        Re: [PATCH-tip v5 17/21] TP-futex: Group readers together in wait queue valdis.kletnieks@vt.edu - 2017-02-03 20:30 +0100
  [PATCH-tip v5 05/21] futex: Add helpers to get & cmpxchg futex value without lock Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100
  [PATCH-tip v5 04/21] futex: Rename futex_pi_state to futex_state Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100
  [PATCH-tip v5 10/21] TP-futex: Enable robust handling Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100
  [PATCH-tip v5 08/21] futex: Allow direct attachment of futex_state objects to hash bucket Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100
  [PATCH-tip v5 03/21] futex: Consolidate duplicated timer setup code Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100
  [PATCH-tip v5 19/21] perf bench: Extend mutex/rwlock futex suite to test TP futexes Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100
  [PATCH-tip v5 11/21] TP-futex: Implement lock handoff to prevent lock starvation Waiman Long <longman@redhat.com> - 2017-02-03 19:10 +0100

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