linux-kernel - [patch] futex: PI state locking fix

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Message-ID: <20070312091342.GA27425@elte.hu>
Date:	Mon, 12 Mar 2007 10:13:42 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	Theodore Tso <tytso@....edu>
Subject: [patch] futex: PI state locking fix

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