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Subject[patch] futex: PI state locking fix
Subject: [patch] futex: PI state locking fix
From: Ingo Molnar <mingo@elte.hu>

testing of -rt by IBM uncovered a locking bug in wake_futex_pi(): the PI
state needs to be locked before we access it.

this patch has been tested in -rt. Must-have for v2.6.21.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
--
kernel/futex.c | 2 ++
1 file changed, 2 insertions(+)

Index: linux/kernel/futex.c
===================================================================
--- linux.orig/kernel/futex.c
+++ linux/kernel/futex.c
@@ -566,6 +566,7 @@ static int wake_futex_pi(u32 __user *uad
if (!pi_state)
return -EINVAL;

+ spin_lock(&pi_state->pi_mutex.wait_lock);
new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);

/*
@@ -605,6 +606,7 @@ static int wake_futex_pi(u32 __user *uad
pi_state->owner = new_owner;
spin_unlock_irq(&new_owner->pi_lock);

+ spin_unlock(&pi_state->pi_mutex.wait_lock);
rt_mutex_unlock(&pi_state->pi_mutex);

return 0;
-
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