From 65810f0ef05e8c9e333f17a44e77808b163ca298 Mon Sep 17 00:00:00 2001 From: Torvald Riegel Date: Thu, 22 Dec 2016 10:20:43 +0100 Subject: 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. --- nptl/pthread_mutex_cond_lock.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'nptl/pthread_mutex_cond_lock.c') diff --git a/nptl/pthread_mutex_cond_lock.c b/nptl/pthread_mutex_cond_lock.c index 2ac421fd63..bd7149ef1d 100644 --- a/nptl/pthread_mutex_cond_lock.c +++ b/nptl/pthread_mutex_cond_lock.c @@ -11,9 +11,9 @@ lll_cond_trylock ((mutex)->__data.__lock) #define LLL_MUTEX_TRYLOCK_ELISION(mutex) LLL_MUTEX_TRYLOCK(mutex) -#define LLL_ROBUST_MUTEX_LOCK(mutex, id) \ - lll_robust_cond_lock ((mutex)->__data.__lock, id, \ - PTHREAD_ROBUST_MUTEX_PSHARED (mutex)) +/* We need to assume that there are other threads blocked on the futex. + See __pthread_mutex_lock_full for further details. */ +#define LLL_ROBUST_MUTEX_LOCK_MODIFIER FUTEX_WAITERS #define __pthread_mutex_lock internal_function __pthread_mutex_cond_lock #define __pthread_mutex_lock_full __pthread_mutex_cond_lock_full #define NO_INCR -- cgit 1.4.1