linux-kernel - [tip:core/urgent] futex: unlock before returning -EFAULT

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Date:	Fri, 13 Mar 2009 00:24:31 GMT
From:	Darren Hart <dvhltc@...ibm.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, dvhltc@...ibm.com, hpa@...or.com,
	mingo@...hat.com, rusty@...tcorp.com.au, peterz@...radead.org,
	tglx@...utronix.de, mingo@...e.hu
Subject: [tip:core/urgent] futex: unlock before returning -EFAULT

Commit-ID:  3d7bdf7880ea243f25cddd847ca65475ed627e5f
Gitweb:     http://git.kernel.org/tip/3d7bdf7880ea243f25cddd847ca65475ed627e5f
Author:     Darren Hart <dvhltc@...ibm.com>
AuthorDate: Thu, 12 Mar 2009 00:56:06 -0700
Commit:     Ingo Molnar <mingo@...e.hu>
CommitDate: Fri, 13 Mar 2009 01:21:00 +0100

futex: unlock before returning -EFAULT

Impact: rt-mutex failure case fix

futex_lock_pi can potentially return -EFAULT with the rt_mutex
held.  This seems like the wrong thing to do as userspace should
assume -EFAULT means the lock was not taken.  Even if it could
figure this out, we'd be leaving the pi_state->owner in an
inconsistent state.  This patch unlocks the rt_mutex prior to
returning -EFAULT to userspace.

Build and boot tested on a 4 way Intel x86_64 workstation.
Passes basic pthread_mutex and PI tests out of
ltp/testcases/realtime.

Signed-off-by: Darren Hart <dvhltc@...ibm.com>
Acked-by: Peter Zijlstra <peterz@...radead.org>
Cc: Rusty Russell <rusty@...tcorp.com.au>
LKML-Reference: <20090312075606.9856.88729.stgit@...n>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 kernel/futex.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index a66cd2d..7e0a916 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1570,6 +1570,13 @@ retry_locked:
 		}
 	}
 
+	/*
+	 * If fixup_pi_state_owner() faulted and was unable to handle the
+	 * fault, unlock it and return the fault to userspace.
+	 */
+	if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
+		rt_mutex_unlock(&q.pi_state->pi_mutex);
+
 	/* Unqueue and drop the lock */
 	unqueue_me_pi(&q);
 
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