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Add compiler barriers around modifications of the robust mutex list for pthread_mutex_trylock. [BZ #24180]

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While debugging a kernel warning, Thomas Gleixner, Sebastian Sewior and
Heiko Carstens found a bug in pthread_mutex_trylock due to misordered
instructions:
140:   a5 1b 00 01             oill    %r1,1
144:   e5 48 a0 f0 00 00       mvghi   240(%r10),0   <--- THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
14a:   e3 10 a0 e0 00 24       stg     %r1,224(%r10) <--- last THREAD_SETMEM of ENQUEUE_MUTEX_PI

vs (with compiler barriers):
140:   a5 1b 00 01             oill    %r1,1
144:   e3 10 a0 e0 00 24       stg     %r1,224(%r10)
14a:   e5 48 a0 f0 00 00       mvghi   240(%r10),0

Please have a look at the discussion:
"Re: WARN_ON_ONCE(!new_owner) within wake_futex_pi() triggerede"
(https://lore.kernel.org/lkml/20190202112006.GB3381@osiris/)

This patch is introducing the same compiler barriers and comments
for pthread_mutex_trylock as introduced for pthread_mutex_lock and
pthread_mutex_timedlock by commit 8f9450a0b7
"Add compiler barriers around modifications of the robust mutex list."

ChangeLog:

	[BZ #24180]
	* nptl/pthread_mutex_trylock.c (__pthread_mutex_trylock):
This commit is contained in:
Stefan Liebler 2019-02-07 15:18:36 +01:00
parent 8311c83f91
commit 823624bdc4
2 changed files with 59 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
ChangeLog
View File

@ -1,3 +1,9 @@
2019-02-07 Stefan Liebler <stli@linux.ibm.com>
[BZ #24180]
* nptl/pthread_mutex_trylock.c (__pthread_mutex_trylock):
Add compiler barriers and comments.
2019-02-07 Florian Weimer <fweimer@redhat.com>
* include/array_length.h (array_length): Do not use a statement

49
nptl/pthread_mutex_trylock.c
View File

@ -94,6 +94,9 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
case PTHREAD_MUTEX_ROBUST_ADAPTIVE_NP:
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
&mutex->__data.__list.__next);
/* We need to set op_pending before starting the operation. Also
see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
oldval = mutex->__data.__lock;
do
@ -119,7 +122,12 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
/* But it is inconsistent unless marked otherwise. */
mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
/* We must not enqueue the mutex before we have acquired it.
Also see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
ENQUEUE_MUTEX (mutex);
/* We need to clear op_pending after we enqueue the mutex. */
__asm ("" ::: "memory");
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
/* Note that we deliberately exist here. If we fall
@ -135,6 +143,8 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
int kind = PTHREAD_MUTEX_TYPE (mutex);
if (kind == PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
{
/* We do not need to ensure ordering wrt another memory
access. Also see comments at ENQUEUE_MUTEX. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
NULL);
return EDEADLK;
@ -142,6 +152,8 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
if (kind == PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
{
/* We do not need to ensure ordering wrt another memory
access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
NULL);
@ -160,6 +172,9 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
id, 0);
if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
{
/* We haven't acquired the lock as it is already acquired by
another owner. We do not need to ensure ordering wrt another
memory access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return EBUSY;
@ -173,13 +188,20 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
if (oldval == id)
lll_unlock (mutex->__data.__lock,
PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
/* FIXME This violates the mutex destruction requirements. See
__pthread_mutex_unlock_full. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return ENOTRECOVERABLE;
}
}
while ((oldval & FUTEX_OWNER_DIED) != 0);
/* We must not enqueue the mutex before we have acquired it.
Also see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
ENQUEUE_MUTEX (mutex);
/* We need to clear op_pending after we enqueue the mutex. */
__asm ("" ::: "memory");
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
mutex->__data.__owner = id;
@ -211,10 +233,15 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
}
if (robust)
{
/* Note: robust PI futexes are signaled by setting bit 0. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
(void *) (((uintptr_t) &mutex->__data.__list.__next)
| 1));
/* We need to set op_pending before starting the operation. Also
see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
}
oldval = mutex->__data.__lock;
@ -223,12 +250,16 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
{
if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
{
/* We do not need to ensure ordering wrt another memory
access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return EDEADLK;
}
if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
{
/* We do not need to ensure ordering wrt another memory
access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
/* Just bump the counter. */
@ -250,6 +281,9 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
{
if ((oldval & FUTEX_OWNER_DIED) == 0)
{
/* We haven't acquired the lock as it is already acquired by
another owner. We do not need to ensure ordering wrt another
memory access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return EBUSY;
@ -270,6 +304,9 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
if (INTERNAL_SYSCALL_ERROR_P (e, __err)
&& INTERNAL_SYSCALL_ERRNO (e, __err) == EWOULDBLOCK)
{
/* The kernel has not yet finished the mutex owner death.
We do not need to ensure ordering wrt another memory
access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return EBUSY;
@ -287,7 +324,12 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
/* But it is inconsistent unless marked otherwise. */
mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
/* We must not enqueue the mutex before we have acquired it.
Also see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
ENQUEUE_MUTEX (mutex);
/* We need to clear op_pending after we enqueue the mutex. */
__asm ("" ::: "memory");
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
/* Note that we deliberately exit here. If we fall
@ -310,13 +352,20 @@ __pthread_mutex_trylock (pthread_mutex_t *mutex)
PTHREAD_ROBUST_MUTEX_PSHARED (mutex)),
0, 0);
/* To the kernel, this will be visible after the kernel has
acquired the mutex in the syscall. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return ENOTRECOVERABLE;
}
if (robust)
{
/* We must not enqueue the mutex before we have acquired it.
Also see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
ENQUEUE_MUTEX_PI (mutex);
/* We need to clear op_pending after we enqueue the mutex. */
__asm ("" ::: "memory");
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
}