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

Darren Hart
2009-03-13T00:25:37Z

Commit-ID: 3d7bdf7880ea243f25cddd847ca65475ed627e5f
Gitweb: http://git.kernel.org/tip/3d7bdf7880ea243f25cddd847ca65475ed627e5f
Author: Darren Hart <dvhltc@us.ibm.com>
AuthorDate: Thu, 12 Mar 2009 00:56:06 -0700
Commit: Ingo Molnar <mingo@elte.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@us.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
LKML-Reference: <20090312075606.9856.88729.stgit@Aeon>
Signed-off-by: Ingo Molnar <mingo@elte.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);