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authorTorvald Riegel <triegel@redhat.com>2016-12-22 10:20:43 +0100
committerTorvald Riegel <triegel@redhat.com>2017-01-13 17:16:07 +0100
commit65810f0ef05e8c9e333f17a44e77808b163ca298 (patch)
tree09928382f6015251c3b351650204f65fc8d6ec21 /sysdeps/nptl
parentf32941d80c7f532031061f8dd4704fab9c275cfe (diff)
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robust mutexes: Fix broken x86 assembly by removing it
lll_robust_unlock on i386 and x86_64 first sets the futex word to FUTEX_WAITERS|0 before calling __lll_unlock_wake, which will set the futex word to 0. If the thread is killed between these steps, then the futex word will be FUTEX_WAITERS|0, and the kernel (at least current upstream) will not set it to FUTEX_OWNER_DIED|FUTEX_WAITERS because 0 is not equal to the TID of the crashed thread. The lll_robust_lock assembly code on i386 and x86_64 is not prepared to deal with this case because the fastpath tries to only CAS 0 to TID and not FUTEX_WAITERS|0 to TID; the slowpath simply waits until it can CAS 0 to TID or the futex_word has the FUTEX_OWNER_DIED bit set. This issue is fixed by removing the custom x86 assembly code and using the generic C code instead. However, instead of adding more duplicate code to the custom x86 lowlevellock.h, the code of the lll_robust* functions is inlined into the single call sites that exist for each of these functions in the pthread_mutex_* functions. The robust mutex paths in the latter have been slightly reorganized to make them simpler. This patch is meant to be easy to backport, so C11-style atomics are not used. [BZ #20985] * nptl/Makefile: Adapt. * nptl/pthread_mutex_cond_lock.c (LLL_ROBUST_MUTEX_LOCK): Remove. (LLL_ROBUST_MUTEX_LOCK_MODIFIER): New. * nptl/pthread_mutex_lock.c (LLL_ROBUST_MUTEX_LOCK): Remove. (LLL_ROBUST_MUTEX_LOCK_MODIFIER): New. (__pthread_mutex_lock_full): Inline lll_robust* functions and adapt. * nptl/pthread_mutex_timedlock.c (pthread_mutex_timedlock): Inline lll_robust* functions and adapt. * nptl/pthread_mutex_unlock.c (__pthread_mutex_unlock_full): Likewise. * sysdeps/nptl/lowlevellock.h (__lll_robust_lock_wait, __lll_robust_lock, lll_robust_cond_lock, __lll_robust_timedlock_wait, __lll_robust_timedlock, __lll_robust_unlock): Remove. * sysdeps/unix/sysv/linux/i386/lowlevellock.h (lll_robust_lock, lll_robust_cond_lock, lll_robust_timedlock, lll_robust_unlock): Remove. * sysdeps/unix/sysv/linux/x86_64/lowlevellock.h (lll_robust_lock, lll_robust_cond_lock, lll_robust_timedlock, lll_robust_unlock): Remove. * sysdeps/unix/sysv/linux/sparc/lowlevellock.h (__lll_robust_lock_wait, __lll_robust_lock, lll_robust_cond_lock, __lll_robust_timedlock_wait, __lll_robust_timedlock, __lll_robust_unlock): Remove. * nptl/lowlevelrobustlock.c: Remove file. * nptl/lowlevelrobustlock.sym: Likewise. * sysdeps/unix/sysv/linux/i386/lowlevelrobustlock.S: Likewise. * sysdeps/unix/sysv/linux/x86_64/lowlevelrobustlock.S: Likewise.
Diffstat (limited to 'sysdeps/nptl')
-rw-r--r--sysdeps/nptl/lowlevellock.h68
1 files changed, 0 insertions, 68 deletions
diff --git a/sysdeps/nptl/lowlevellock.h b/sysdeps/nptl/lowlevellock.h
index 36a76fab08..42d9658d9d 100644
--- a/sysdeps/nptl/lowlevellock.h
+++ b/sysdeps/nptl/lowlevellock.h
@@ -74,7 +74,6 @@
extern void __lll_lock_wait_private (int *futex) attribute_hidden;
extern void __lll_lock_wait (int *futex, int private) attribute_hidden;
-extern int __lll_robust_lock_wait (int *futex, int private) attribute_hidden;
/* This is an expression rather than a statement even though its value is
void, so that it can be used in a comma expression or as an expression
@@ -103,28 +102,6 @@ extern int __lll_robust_lock_wait (int *futex, int private) attribute_hidden;
__lll_lock (&(futex), private)
-/* If FUTEX is 0 (not acquired), set to ID (acquired with no waiters) and
- return 0. Otherwise, ensure that it is set to FUTEX | FUTEX_WAITERS
- (acquired, possibly with waiters) and block until we acquire the lock.
- FUTEX will now be ID | FUTEX_WAITERS and we return 0.
- If the previous owner of the lock dies before we acquire the lock then FUTEX
- will be the value of id as set by the previous owner, with FUTEX_OWNER_DIED
- set (FUTEX_WAITERS may or may not be set). We return this value to indicate
- that the lock is not acquired. */
-#define __lll_robust_lock(futex, id, private) \
- ({ \
- int *__futex = (futex); \
- int __val = 0; \
- \
- if (__glibc_unlikely \
- (atomic_compare_and_exchange_bool_acq (__futex, id, 0))) \
- __val = __lll_robust_lock_wait (__futex, private); \
- __val; \
- })
-#define lll_robust_lock(futex, id, private) \
- __lll_robust_lock (&(futex), id, private)
-
-
/* This is an expression rather than a statement even though its value is
void, so that it can be used in a comma expression or as an expression
that's cast to void. */
@@ -142,16 +119,8 @@ extern int __lll_robust_lock_wait (int *futex, int private) attribute_hidden;
#define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private)
-/* As __lll_robust_lock, but set to ID | FUTEX_WAITERS (acquired, possibly with
- waiters) if FUTEX is 0. */
-#define lll_robust_cond_lock(futex, id, private) \
- __lll_robust_lock (&(futex), (id) | FUTEX_WAITERS, private)
-
-
extern int __lll_timedlock_wait (int *futex, const struct timespec *,
int private) attribute_hidden;
-extern int __lll_robust_timedlock_wait (int *futex, const struct timespec *,
- int private) attribute_hidden;
/* As __lll_lock, but with a timeout. If the timeout occurs then return
@@ -170,22 +139,6 @@ extern int __lll_robust_timedlock_wait (int *futex, const struct timespec *,
__lll_timedlock (&(futex), abstime, private)
-/* As __lll_robust_lock, but with a timeout. If the timeout occurs then return
- ETIMEDOUT. If ABSTIME is invalid, return EINVAL. */
-#define __lll_robust_timedlock(futex, abstime, id, private) \
- ({ \
- int *__futex = (futex); \
- int __val = 0; \
- \
- if (__glibc_unlikely \
- (atomic_compare_and_exchange_bool_acq (__futex, id, 0))) \
- __val = __lll_robust_timedlock_wait (__futex, abstime, private); \
- __val; \
- })
-#define lll_robust_timedlock(futex, abstime, id, private) \
- __lll_robust_timedlock (&(futex), abstime, id, private)
-
-
/* This is an expression rather than a statement even though its value is
void, so that it can be used in a comma expression or as an expression
that's cast to void. */
@@ -211,27 +164,6 @@ extern int __lll_robust_timedlock_wait (int *futex, const struct timespec *,
__lll_unlock (&(futex), private)
-/* This is an expression rather than a statement even though its value is
- void, so that it can be used in a comma expression or as an expression
- that's cast to void. */
-/* Unconditionally set FUTEX to 0 (not acquired), releasing the lock. If FUTEX
- had FUTEX_WAITERS set then wake any waiters. The waiter that acquires the
- lock will set FUTEX_WAITERS.
- Evaluate PRIVATE before releasing the lock so that we do not violate the
- mutex destruction requirements (see __lll_unlock). */
-#define __lll_robust_unlock(futex, private) \
- ((void) \
- ({ \
- int *__futex = (futex); \
- int __private = (private); \
- int __oldval = atomic_exchange_rel (__futex, 0); \
- if (__glibc_unlikely (__oldval & FUTEX_WAITERS)) \
- lll_futex_wake (__futex, 1, __private); \
- }))
-#define lll_robust_unlock(futex, private) \
- __lll_robust_unlock (&(futex), private)
-
-
#define lll_islocked(futex) \
((futex) != LLL_LOCK_INITIALIZER)