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commit 823624bdc47f1f80109c9c52dee7939b9386d708
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Author: Stefan Liebler <stli@linux.ibm.com>
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Date: Thu Feb 7 15:18:36 2019 +0100
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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
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Heiko Carstens found a bug in pthread_mutex_trylock due to misordered
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instructions:
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140: a5 1b 00 01 oill %r1,1
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144: e5 48 a0 f0 00 00 mvghi 240(%r10),0 <--- THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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14a: e3 10 a0 e0 00 24 stg %r1,224(%r10) <--- last THREAD_SETMEM of ENQUEUE_MUTEX_PI
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vs (with compiler barriers):
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140: a5 1b 00 01 oill %r1,1
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144: e3 10 a0 e0 00 24 stg %r1,224(%r10)
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14a: e5 48 a0 f0 00 00 mvghi 240(%r10),0
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Please have a look at the discussion:
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"Re: WARN_ON_ONCE(!new_owner) within wake_futex_pi() triggerede"
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(https://lore.kernel.org/lkml/20190202112006.GB3381@osiris/)
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This patch is introducing the same compiler barriers and comments
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for pthread_mutex_trylock as introduced for pthread_mutex_lock and
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pthread_mutex_timedlock by commit 8f9450a0b7a9e78267e8ae1ab1000ebca08e473e
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"Add compiler barriers around modifications of the robust mutex list."
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ChangeLog:
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[BZ #24180]
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* nptl/pthread_mutex_trylock.c (__pthread_mutex_trylock):
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diff -Nrup a/nptl/pthread_mutex_trylock.c b/nptl/pthread_mutex_trylock.c
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--- a/nptl/pthread_mutex_trylock.c 2019-07-26 16:43:11.028271897 -0400
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+++ b/nptl/pthread_mutex_trylock.c 2019-07-26 17:06:48.708748979 -0400
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@@ -95,6 +95,9 @@ __pthread_mutex_trylock (pthread_mutex_t
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case PTHREAD_MUTEX_ROBUST_ADAPTIVE_NP:
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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&mutex->__data.__list.__next);
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+ /* We need to set op_pending before starting the operation. Also
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+ see comments at ENQUEUE_MUTEX. */
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+ __asm ("" ::: "memory");
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oldval = mutex->__data.__lock;
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do
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@@ -120,7 +123,12 @@ __pthread_mutex_trylock (pthread_mutex_t
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/* But it is inconsistent unless marked otherwise. */
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mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
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+ /* We must not enqueue the mutex before we have acquired it.
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+ Also see comments at ENQUEUE_MUTEX. */
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+ __asm ("" ::: "memory");
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ENQUEUE_MUTEX (mutex);
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+ /* We need to clear op_pending after we enqueue the mutex. */
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+ __asm ("" ::: "memory");
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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/* Note that we deliberately exist here. If we fall
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@@ -136,6 +144,8 @@ __pthread_mutex_trylock (pthread_mutex_t
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int kind = PTHREAD_MUTEX_TYPE (mutex);
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if (kind == PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
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{
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+ /* We do not need to ensure ordering wrt another memory
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+ access. Also see comments at ENQUEUE_MUTEX. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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NULL);
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return EDEADLK;
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@@ -143,6 +153,8 @@ __pthread_mutex_trylock (pthread_mutex_t
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if (kind == PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
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{
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+ /* We do not need to ensure ordering wrt another memory
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+ access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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NULL);
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@@ -160,6 +172,10 @@ __pthread_mutex_trylock (pthread_mutex_t
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oldval = lll_robust_trylock (mutex->__data.__lock, id);
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if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
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{
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+ /* We haven't acquired the lock as it is already acquired by
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+ another owner. We do not need to ensure ordering wrt another
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+ memory access. */
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+
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EBUSY;
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@@ -173,13 +189,20 @@ __pthread_mutex_trylock (pthread_mutex_t
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if (oldval == id)
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lll_unlock (mutex->__data.__lock,
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PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
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+ /* FIXME This violates the mutex destruction requirements. See
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+ __pthread_mutex_unlock_full. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return ENOTRECOVERABLE;
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}
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}
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while ((oldval & FUTEX_OWNER_DIED) != 0);
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+ /* We must not enqueue the mutex before we have acquired it.
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+ Also see comments at ENQUEUE_MUTEX. */
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+ __asm ("" ::: "memory");
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ENQUEUE_MUTEX (mutex);
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+ /* We need to clear op_pending after we enqueue the mutex. */
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+ __asm ("" ::: "memory");
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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mutex->__data.__owner = id;
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@@ -201,10 +224,15 @@ __pthread_mutex_trylock (pthread_mutex_t
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int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
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if (robust)
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- /* Note: robust PI futexes are signaled by setting bit 0. */
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- THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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- (void *) (((uintptr_t) &mutex->__data.__list.__next)
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- | 1));
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+ {
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+ /* Note: robust PI futexes are signaled by setting bit 0. */
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+ THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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+ (void *) (((uintptr_t) &mutex->__data.__list.__next)
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+ | 1));
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+ /* We need to set op_pending before starting the operation. Also
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+ see comments at ENQUEUE_MUTEX. */
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+ __asm ("" ::: "memory");
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+ }
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oldval = mutex->__data.__lock;
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@@ -213,12 +241,16 @@ __pthread_mutex_trylock (pthread_mutex_t
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{
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if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
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{
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+ /* We do not need to ensure ordering wrt another memory
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+ access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EDEADLK;
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}
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if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
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{
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+ /* We do not need to ensure ordering wrt another memory
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+ access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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/* Just bump the counter. */
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@@ -240,6 +272,9 @@ __pthread_mutex_trylock (pthread_mutex_t
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{
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if ((oldval & FUTEX_OWNER_DIED) == 0)
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{
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+ /* We haven't acquired the lock as it is already acquired by
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+ another owner. We do not need to ensure ordering wrt another
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+ memory access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EBUSY;
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@@ -260,6 +295,9 @@ __pthread_mutex_trylock (pthread_mutex_t
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if (INTERNAL_SYSCALL_ERROR_P (e, __err)
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&& INTERNAL_SYSCALL_ERRNO (e, __err) == EWOULDBLOCK)
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{
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+ /* The kernel has not yet finished the mutex owner death.
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+ We do not need to ensure ordering wrt another memory
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+ access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EBUSY;
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@@ -277,7 +315,12 @@ __pthread_mutex_trylock (pthread_mutex_t
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/* But it is inconsistent unless marked otherwise. */
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mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
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+ /* We must not enqueue the mutex before we have acquired it.
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+ Also see comments at ENQUEUE_MUTEX. */
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+ __asm ("" ::: "memory");
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ENQUEUE_MUTEX (mutex);
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+ /* We need to clear op_pending after we enqueue the mutex. */
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+ __asm ("" ::: "memory");
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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/* Note that we deliberately exit here. If we fall
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@@ -300,13 +343,20 @@ __pthread_mutex_trylock (pthread_mutex_t
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PTHREAD_ROBUST_MUTEX_PSHARED (mutex)),
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0, 0);
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+ /* To the kernel, this will be visible after the kernel has
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+ acquired the mutex in the syscall. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return ENOTRECOVERABLE;
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}
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if (robust)
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{
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+ /* We must not enqueue the mutex before we have acquired it.
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+ Also see comments at ENQUEUE_MUTEX. */
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+ __asm ("" ::: "memory");
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ENQUEUE_MUTEX_PI (mutex);
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+ /* We need to clear op_pending after we enqueue the mutex. */
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+ __asm ("" ::: "memory");
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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}
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