Take lock in pthread_cond_wait cleanup handler only when needed

[BZ #14652]
When a thread waiting in pthread_cond_wait with a PI mutex is
cancelled after it has returned successfully from the futex syscall
but just before async cancellation is disabled, it enters its
cancellation handler with the mutex held and simply calling a
mutex_lock again will result in a deadlock.  Hence, it is necessary to
see if the thread owns the lock and try to lock it only if it doesn't.

1 files changed, 16 insertions, 2 deletions

diff --git a/nptl/sysdeps/unix/sysv/linux/i386/i486/pthread_cond_timedwait.S b/nptl/sysdeps/unix/sysv/linux/i386/i486/pthread_cond_timedwait.S
index 6761c136e5..884987cf50 100644
--- a/nptl/sysdeps/unix/sysv/linux/i386/i486/pthread_cond_timedwait.S
+++ b/nptl/sysdeps/unix/sysv/linux/i386/i486/pthread_cond_timedwait.S
@@ -649,10 +649,24 @@ __condvar_tw_cleanup:
 	movl	$0x7fffffff, %edx
 	ENTER_KERNEL
 
+	/* Lock the mutex only if we don't own it already.  This only happens
+	   in case of PI mutexes, if we got cancelled after a successful
+	   return of the futex syscall and before disabling async
+	   cancellation.  */
 5:	movl	24+FRAME_SIZE(%esp), %eax
-	call	__pthread_mutex_cond_lock
+	movl	MUTEX_KIND(%eax), %ebx
+	andl	$(ROBUST_BIT|PI_BIT), %ebx
+	cmpl	$PI_BIT, %ebx
+	jne	8f
+
+	movl	(%eax), %ebx
+	andl	$TID_MASK, %ebx
+	cmpl	%ebx, %gs:TID
+	je	9f
+
+8:	call	__pthread_mutex_cond_lock
 
-	movl	%esi, (%esp)
+9:	movl	%esi, (%esp)
 .LcallUR:
 	call	_Unwind_Resume
 	hlt