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glibc-utils
force-elision-race.patch
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File force-elision-race.patch of Package glibc-utils
2018-10-17 Stefan Liebler <stli@linux.ibm.com> [BZ #23275] * sysdeps/unix/sysv/linux/s390/force-elision.h: (FORCE_ELISION): Ensure that elision path is used if elision is available. * sysdeps/unix/sysv/linux/powerpc/force-elision.h (FORCE_ELISION): Likewise. * sysdeps/unix/sysv/linux/x86/force-elision.h: (FORCE_ELISION): Likewise. * nptl/pthreadP.h (PTHREAD_MUTEX_TYPE, PTHREAD_MUTEX_TYPE_ELISION) (PTHREAD_MUTEX_PSHARED): Use atomic_load_relaxed. * nptl/pthread_mutex_consistent.c (pthread_mutex_consistent): Likewise. * nptl/pthread_mutex_getprioceiling.c (pthread_mutex_getprioceiling): Likewise. * nptl/pthread_mutex_lock.c (__pthread_mutex_lock_full) (__pthread_mutex_cond_lock_adjust): Likewise. * nptl/pthread_mutex_setprioceiling.c (pthread_mutex_setprioceiling): Likewise. * nptl/pthread_mutex_timedlock.c (__pthread_mutex_timedlock): Likewise. * nptl/pthread_mutex_trylock.c (__pthread_mutex_trylock): Likewise. * nptl/pthread_mutex_unlock.c (__pthread_mutex_unlock_full): Likewise. * sysdeps/nptl/bits/thread-shared-types.h (struct __pthread_mutex_s): Add comments. * nptl/pthread_mutex_destroy.c (__pthread_mutex_destroy): Use atomic_load_relaxed and atomic_store_relaxed. * nptl/pthread_mutex_init.c (__pthread_mutex_init): Use atomic_store_relaxed. Index: glibc-2.22/nptl/pthreadP.h =================================================================== --- glibc-2.22.orig/nptl/pthreadP.h +++ glibc-2.22/nptl/pthreadP.h @@ -110,19 +110,23 @@ enum }; #define PTHREAD_MUTEX_PSHARED_BIT 128 +/* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ #define PTHREAD_MUTEX_TYPE(m) \ - ((m)->__data.__kind & 127) + (atomic_load_relaxed (&((m)->__data.__kind)) & 127) /* Don't include NO_ELISION, as that type is always the same as the underlying lock type. */ #define PTHREAD_MUTEX_TYPE_ELISION(m) \ - ((m)->__data.__kind & (127|PTHREAD_MUTEX_ELISION_NP)) + (atomic_load_relaxed (&((m)->__data.__kind)) \ + & (127 | PTHREAD_MUTEX_ELISION_NP)) #if LLL_PRIVATE == 0 && LLL_SHARED == 128 # define PTHREAD_MUTEX_PSHARED(m) \ - ((m)->__data.__kind & 128) + (atomic_load_relaxed (&((m)->__data.__kind)) & 128) #else # define PTHREAD_MUTEX_PSHARED(m) \ - (((m)->__data.__kind & 128) ? LLL_SHARED : LLL_PRIVATE) + ((atomic_load_relaxed (&((m)->__data.__kind)) & 128) \ + ? LLL_SHARED : LLL_PRIVATE) #endif /* The kernel when waking robust mutexes on exit never uses Index: glibc-2.22/nptl/pthread_mutex_consistent.c =================================================================== --- glibc-2.22.orig/nptl/pthread_mutex_consistent.c +++ glibc-2.22/nptl/pthread_mutex_consistent.c @@ -24,8 +24,11 @@ int pthread_mutex_consistent (mutex) pthread_mutex_t *mutex; { - /* Test whether this is a robust mutex with a dead owner. */ - if ((mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP) == 0 + /* Test whether this is a robust mutex with a dead owner. + See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + if ((atomic_load_relaxed (&(mutex->__data.__kind)) + & PTHREAD_MUTEX_ROBUST_NORMAL_NP) == 0 || mutex->__data.__owner != PTHREAD_MUTEX_INCONSISTENT) return EINVAL; Index: glibc-2.22/nptl/pthread_mutex_destroy.c =================================================================== --- glibc-2.22.orig/nptl/pthread_mutex_destroy.c +++ glibc-2.22/nptl/pthread_mutex_destroy.c @@ -28,12 +28,17 @@ __pthread_mutex_destroy (mutex) { LIBC_PROBE (mutex_destroy, 1, mutex); - if ((mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP) == 0 + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + if ((atomic_load_relaxed (&(mutex->__data.__kind)) + & PTHREAD_MUTEX_ROBUST_NORMAL_NP) == 0 && mutex->__data.__nusers != 0) return EBUSY; - /* Set to an invalid value. */ - mutex->__data.__kind = -1; + /* Set to an invalid value. Relaxed MO is enough as it is undefined behavior + if the mutex is used after it has been destroyed. But you can reinitialize + it with pthread_mutex_init. */ + atomic_store_relaxed (&(mutex->__data.__kind), -1); return 0; } Index: glibc-2.22/nptl/pthread_mutex_getprioceiling.c =================================================================== --- glibc-2.22.orig/nptl/pthread_mutex_getprioceiling.c +++ glibc-2.22/nptl/pthread_mutex_getprioceiling.c @@ -26,7 +26,9 @@ pthread_mutex_getprioceiling (mutex, pri const pthread_mutex_t *mutex; int *prioceiling; { - if (__builtin_expect ((mutex->__data.__kind + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + if (__builtin_expect ((atomic_load_relaxed (&(((pthread_mutex_t *) mutex)->__data.__kind)) & PTHREAD_MUTEX_PRIO_PROTECT_NP) == 0, 0)) return EINVAL; Index: glibc-2.22/nptl/pthread_mutex_init.c =================================================================== --- glibc-2.22.orig/nptl/pthread_mutex_init.c +++ glibc-2.22/nptl/pthread_mutex_init.c @@ -91,7 +91,7 @@ __pthread_mutex_init (mutex, mutexattr) memset (mutex, '\0', __SIZEOF_PTHREAD_MUTEX_T); /* Copy the values from the attribute. */ - mutex->__data.__kind = imutexattr->mutexkind & ~PTHREAD_MUTEXATTR_FLAG_BITS; + int mutex_kind = imutexattr->mutexkind & ~PTHREAD_MUTEXATTR_FLAG_BITS; if ((imutexattr->mutexkind & PTHREAD_MUTEXATTR_FLAG_ROBUST) != 0) { @@ -101,17 +101,17 @@ __pthread_mutex_init (mutex, mutexattr) return ENOTSUP; #endif - mutex->__data.__kind |= PTHREAD_MUTEX_ROBUST_NORMAL_NP; + mutex_kind |= PTHREAD_MUTEX_ROBUST_NORMAL_NP; } switch (imutexattr->mutexkind & PTHREAD_MUTEXATTR_PROTOCOL_MASK) { case PTHREAD_PRIO_INHERIT << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT: - mutex->__data.__kind |= PTHREAD_MUTEX_PRIO_INHERIT_NP; + mutex_kind |= PTHREAD_MUTEX_PRIO_INHERIT_NP; break; case PTHREAD_PRIO_PROTECT << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT: - mutex->__data.__kind |= PTHREAD_MUTEX_PRIO_PROTECT_NP; + mutex_kind |= PTHREAD_MUTEX_PRIO_PROTECT_NP; int ceiling = (imutexattr->mutexkind & PTHREAD_MUTEXATTR_PRIO_CEILING_MASK) @@ -135,7 +135,11 @@ __pthread_mutex_init (mutex, mutexattr) FUTEX_PRIVATE_FLAG FUTEX_WAKE. */ if ((imutexattr->mutexkind & (PTHREAD_MUTEXATTR_FLAG_PSHARED | PTHREAD_MUTEXATTR_FLAG_ROBUST)) != 0) - mutex->__data.__kind |= PTHREAD_MUTEX_PSHARED_BIT; + mutex_kind |= PTHREAD_MUTEX_PSHARED_BIT; + + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + atomic_store_relaxed (&(mutex->__data.__kind), mutex_kind); /* Default values: mutex not used yet. */ // mutex->__count = 0; already done by memset Index: glibc-2.22/nptl/pthread_mutex_lock.c =================================================================== --- glibc-2.22.orig/nptl/pthread_mutex_lock.c +++ glibc-2.22/nptl/pthread_mutex_lock.c @@ -65,6 +65,8 @@ __pthread_mutex_lock (mutex) { assert (sizeof (mutex->__size) >= sizeof (mutex->__data)); + /* See concurrency notes regarding mutex type which is loaded from __kind + in struct __pthread_mutex_s in sysdeps/nptl/bits/thread-shared-types.h. */ unsigned int type = PTHREAD_MUTEX_TYPE_ELISION (mutex); LIBC_PROBE (mutex_entry, 1, mutex); @@ -287,8 +289,14 @@ __pthread_mutex_lock_full (pthread_mutex case PTHREAD_MUTEX_PI_ROBUST_NORMAL_NP: case PTHREAD_MUTEX_PI_ROBUST_ADAPTIVE_NP: { - int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP; - int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP; + int kind, robust; + { + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + int mutex_kind = atomic_load_relaxed (&(mutex->__data.__kind)); + kind = mutex_kind & PTHREAD_MUTEX_KIND_MASK_NP; + robust = mutex_kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP; + } if (robust) /* Note: robust PI futexes are signaled by setting bit 0. */ @@ -418,7 +426,10 @@ __pthread_mutex_lock_full (pthread_mutex case PTHREAD_MUTEX_PP_NORMAL_NP: case PTHREAD_MUTEX_PP_ADAPTIVE_NP: { - int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP; + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + int kind = atomic_load_relaxed (&(mutex->__data.__kind)) + & PTHREAD_MUTEX_KIND_MASK_NP; oldval = mutex->__data.__lock; @@ -524,15 +535,18 @@ void __pthread_mutex_cond_lock_adjust (mutex) pthread_mutex_t *mutex; { - assert ((mutex->__data.__kind & PTHREAD_MUTEX_PRIO_INHERIT_NP) != 0); - assert ((mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP) == 0); - assert ((mutex->__data.__kind & PTHREAD_MUTEX_PSHARED_BIT) == 0); + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + int mutex_kind = atomic_load_relaxed (&(mutex->__data.__kind)); + assert ((mutex_kind & PTHREAD_MUTEX_PRIO_INHERIT_NP) != 0); + assert ((mutex_kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP) == 0); + assert ((mutex_kind & PTHREAD_MUTEX_PSHARED_BIT) == 0); /* Record the ownership. */ pid_t id = THREAD_GETMEM (THREAD_SELF, tid); mutex->__data.__owner = id; - if (mutex->__data.__kind == PTHREAD_MUTEX_PI_RECURSIVE_NP) + if (mutex_kind == PTHREAD_MUTEX_PI_RECURSIVE_NP) ++mutex->__data.__count; } #endif Index: glibc-2.22/nptl/pthread_mutex_setprioceiling.c =================================================================== --- glibc-2.22.orig/nptl/pthread_mutex_setprioceiling.c +++ glibc-2.22/nptl/pthread_mutex_setprioceiling.c @@ -29,9 +29,10 @@ pthread_mutex_setprioceiling (mutex, pri int prioceiling; int *old_ceiling; { - /* The low bits of __kind aren't ever changed after pthread_mutex_init, - so we don't need a lock yet. */ - if ((mutex->__data.__kind & PTHREAD_MUTEX_PRIO_PROTECT_NP) == 0) + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + if ((atomic_load_relaxed (&(mutex->__data.__kind)) + & PTHREAD_MUTEX_PRIO_PROTECT_NP) == 0) return EINVAL; /* See __init_sched_fifo_prio. */ Index: glibc-2.22/nptl/pthread_mutex_timedlock.c =================================================================== --- glibc-2.22.orig/nptl/pthread_mutex_timedlock.c +++ glibc-2.22/nptl/pthread_mutex_timedlock.c @@ -54,6 +54,8 @@ pthread_mutex_timedlock (mutex, abstime) /* We must not check ABSTIME here. If the thread does not block abstime must not be checked for a valid value. */ + /* See concurrency notes regarding mutex type which is loaded from __kind + in struct __pthread_mutex_s in sysdeps/nptl/bits/thread-shared-types.h. */ switch (__builtin_expect (PTHREAD_MUTEX_TYPE_ELISION (mutex), PTHREAD_MUTEX_TIMED_NP)) { @@ -243,8 +245,14 @@ pthread_mutex_timedlock (mutex, abstime) case PTHREAD_MUTEX_PI_ROBUST_NORMAL_NP: case PTHREAD_MUTEX_PI_ROBUST_ADAPTIVE_NP: { - int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP; - int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP; + int kind, robust; + { + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + int mutex_kind = atomic_load_relaxed (&(mutex->__data.__kind)); + kind = mutex_kind & PTHREAD_MUTEX_KIND_MASK_NP; + robust = mutex_kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP; + } if (robust) /* Note: robust PI futexes are signaled by setting bit 0. */ @@ -393,7 +401,10 @@ pthread_mutex_timedlock (mutex, abstime) case PTHREAD_MUTEX_PP_NORMAL_NP: case PTHREAD_MUTEX_PP_ADAPTIVE_NP: { - int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP; + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + int kind = atomic_load_relaxed (&(mutex->__data.__kind)) + & PTHREAD_MUTEX_KIND_MASK_NP; oldval = mutex->__data.__lock; Index: glibc-2.22/nptl/pthread_mutex_trylock.c =================================================================== --- glibc-2.22.orig/nptl/pthread_mutex_trylock.c +++ glibc-2.22/nptl/pthread_mutex_trylock.c @@ -37,6 +37,8 @@ __pthread_mutex_trylock (mutex) int oldval; pid_t id = THREAD_GETMEM (THREAD_SELF, tid); + /* See concurrency notes regarding mutex type which is loaded from __kind + in struct __pthread_mutex_s in sysdeps/nptl/bits/thread-shared-types.h. */ switch (__builtin_expect (PTHREAD_MUTEX_TYPE_ELISION (mutex), PTHREAD_MUTEX_TIMED_NP)) { @@ -200,8 +202,14 @@ __pthread_mutex_trylock (mutex) case PTHREAD_MUTEX_PI_ROBUST_NORMAL_NP: case PTHREAD_MUTEX_PI_ROBUST_ADAPTIVE_NP: { - int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP; - int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP; + int kind, robust; + { + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + int mutex_kind = atomic_load_relaxed (&(mutex->__data.__kind)); + kind = mutex_kind & PTHREAD_MUTEX_KIND_MASK_NP; + robust = mutex_kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP; + } if (robust) /* Note: robust PI futexes are signaled by setting bit 0. */ @@ -326,7 +334,10 @@ __pthread_mutex_trylock (mutex) case PTHREAD_MUTEX_PP_NORMAL_NP: case PTHREAD_MUTEX_PP_ADAPTIVE_NP: { - int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP; + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + int kind = atomic_load_relaxed (&(mutex->__data.__kind)) + & PTHREAD_MUTEX_KIND_MASK_NP; oldval = mutex->__data.__lock; Index: glibc-2.22/nptl/pthread_mutex_unlock.c =================================================================== --- glibc-2.22.orig/nptl/pthread_mutex_unlock.c +++ glibc-2.22/nptl/pthread_mutex_unlock.c @@ -38,6 +38,8 @@ __pthread_mutex_unlock_usercnt (mutex, d pthread_mutex_t *mutex; int decr; { + /* See concurrency notes regarding mutex type which is loaded from __kind + in struct __pthread_mutex_s in sysdeps/nptl/bits/thread-shared-types.h. */ int type = PTHREAD_MUTEX_TYPE_ELISION (mutex); if (__builtin_expect (type & ~(PTHREAD_MUTEX_KIND_MASK_NP|PTHREAD_MUTEX_ELISION_FLAGS_NP), 0)) @@ -209,13 +211,19 @@ __pthread_mutex_unlock_full (pthread_mut /* If the previous owner died and the caller did not succeed in making the state consistent, mark the mutex as unrecoverable and make all waiters. */ - if ((mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP) != 0 + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + if ((atomic_load_relaxed (&(mutex->__data.__kind)) + & PTHREAD_MUTEX_ROBUST_NORMAL_NP) != 0 && __builtin_expect (mutex->__data.__owner == PTHREAD_MUTEX_INCONSISTENT, 0)) pi_notrecoverable: newowner = PTHREAD_MUTEX_NOTRECOVERABLE; - if ((mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP) != 0) + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + if ((atomic_load_relaxed (&(mutex->__data.__kind)) + & PTHREAD_MUTEX_ROBUST_NORMAL_NP) != 0) { continue_pi_robust: /* Remove mutex from the list. @@ -238,7 +246,10 @@ __pthread_mutex_unlock_full (pthread_mut THREAD_GETMEM (THREAD_SELF, tid))) { - int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP; + /* See concurrency notes regarding __kind in struct __pthread_mutex_s + in sysdeps/nptl/bits/thread-shared-types.h. */ + int robust = atomic_load_relaxed (&(mutex->__data.__kind)) + & PTHREAD_MUTEX_ROBUST_NORMAL_NP; int private = (robust ? PTHREAD_ROBUST_MUTEX_PSHARED (mutex) : PTHREAD_MUTEX_PSHARED (mutex)); Index: glibc-2.22/sysdeps/unix/sysv/linux/powerpc/force-elision.h =================================================================== --- glibc-2.22.orig/sysdeps/unix/sysv/linux/powerpc/force-elision.h +++ glibc-2.22/sysdeps/unix/sysv/linux/powerpc/force-elision.h @@ -19,10 +19,46 @@ #ifdef ENABLE_LOCK_ELISION /* Automatically enable elision for existing user lock kinds. */ #define FORCE_ELISION(m, s) \ - if (__pthread_force_elision \ - && (m->__data.__kind & PTHREAD_MUTEX_ELISION_FLAGS_NP) == 0) \ + if (__pthread_force_elision) \ { \ - mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP; \ - s; \ + /* See concurrency notes regarding __kind in \ + struct __pthread_mutex_s in \ + sysdeps/nptl/bits/thread-shared-types.h. \ + \ + There are the following cases for the kind of a mutex \ + (The mask PTHREAD_MUTEX_ELISION_FLAGS_NP covers the flags \ + PTHREAD_MUTEX_ELISION_NP and PTHREAD_MUTEX_NO_ELISION_NP where \ + only one of both flags can be set): \ + - both flags are not set: \ + This is the first lock operation for this mutex. Enable \ + elision as it is not enabled so far. \ + Note: It can happen that multiple threads are calling e.g. \ + pthread_mutex_lock at the same time as the first lock \ + operation for this mutex. Then elision is enabled for this \ + mutex by multiple threads. Storing with relaxed MO is enough \ + as all threads will store the same new value for the kind of \ + the mutex. But we have to ensure that we always use the \ + elision path regardless if this thread has enabled elision or \ + another one. \ + \ + - PTHREAD_MUTEX_ELISION_NP flag is set: \ + Elision was already enabled for this mutex by a previous lock \ + operation. See case above. Just use the elision path. \ + \ + - PTHREAD_MUTEX_NO_ELISION_NP flag is set: \ + Elision was explicitly disabled by pthread_mutexattr_settype. \ + Do not use the elision path. \ + Note: The flag PTHREAD_MUTEX_NO_ELISION_NP will never be \ + changed after mutex initialization. */ \ + int mutex_kind = atomic_load_relaxed (&((m)->__data.__kind)); \ + if ((mutex_kind & PTHREAD_MUTEX_ELISION_FLAGS_NP) == 0) \ + { \ + mutex_kind |= PTHREAD_MUTEX_ELISION_NP; \ + atomic_store_relaxed (&((m)->__data.__kind), mutex_kind); \ + } \ + if ((mutex_kind & PTHREAD_MUTEX_ELISION_NP) != 0) \ + { \ + s; \ + } \ } #endif Index: glibc-2.22/sysdeps/unix/sysv/linux/s390/force-elision.h =================================================================== --- glibc-2.22.orig/sysdeps/unix/sysv/linux/s390/force-elision.h +++ glibc-2.22/sysdeps/unix/sysv/linux/s390/force-elision.h @@ -19,10 +19,46 @@ #ifdef ENABLE_LOCK_ELISION /* Automatically enable elision for existing user lock kinds. */ #define FORCE_ELISION(m, s) \ - if (__pthread_force_elision \ - && (m->__data.__kind & PTHREAD_MUTEX_ELISION_FLAGS_NP) == 0) \ + if (__pthread_force_elision) \ { \ - mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP; \ - s; \ + /* See concurrency notes regarding __kind in \ + struct __pthread_mutex_s in \ + sysdeps/nptl/bits/thread-shared-types.h. \ + \ + There are the following cases for the kind of a mutex \ + (The mask PTHREAD_MUTEX_ELISION_FLAGS_NP covers the flags \ + PTHREAD_MUTEX_ELISION_NP and PTHREAD_MUTEX_NO_ELISION_NP where \ + only one of both flags can be set): \ + - both flags are not set: \ + This is the first lock operation for this mutex. Enable \ + elision as it is not enabled so far. \ + Note: It can happen that multiple threads are calling e.g. \ + pthread_mutex_lock at the same time as the first lock \ + operation for this mutex. Then elision is enabled for this \ + mutex by multiple threads. Storing with relaxed MO is enough \ + as all threads will store the same new value for the kind of \ + the mutex. But we have to ensure that we always use the \ + elision path regardless if this thread has enabled elision or \ + another one. \ + \ + - PTHREAD_MUTEX_ELISION_NP flag is set: \ + Elision was already enabled for this mutex by a previous lock \ + operation. See case above. Just use the elision path. \ + \ + - PTHREAD_MUTEX_NO_ELISION_NP flag is set: \ + Elision was explicitly disabled by pthread_mutexattr_settype. \ + Do not use the elision path. \ + Note: The flag PTHREAD_MUTEX_NO_ELISION_NP will never be \ + changed after mutex initialization. */ \ + int mutex_kind = atomic_load_relaxed (&((m)->__data.__kind)); \ + if ((mutex_kind & PTHREAD_MUTEX_ELISION_FLAGS_NP) == 0) \ + { \ + mutex_kind |= PTHREAD_MUTEX_ELISION_NP; \ + atomic_store_relaxed (&((m)->__data.__kind), mutex_kind); \ + } \ + if ((mutex_kind & PTHREAD_MUTEX_ELISION_NP) != 0) \ + { \ + s; \ + } \ } #endif Index: glibc-2.22/sysdeps/unix/sysv/linux/x86/force-elision.h =================================================================== --- glibc-2.22.orig/sysdeps/unix/sysv/linux/x86/force-elision.h +++ glibc-2.22/sysdeps/unix/sysv/linux/x86/force-elision.h @@ -18,9 +18,45 @@ /* Automatically enable elision for existing user lock kinds. */ #define FORCE_ELISION(m, s) \ - if (__pthread_force_elision \ - && (m->__data.__kind & PTHREAD_MUTEX_ELISION_FLAGS_NP) == 0) \ + if (__pthread_force_elision) \ { \ - mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP; \ - s; \ + /* See concurrency notes regarding __kind in \ + struct __pthread_mutex_s in \ + sysdeps/nptl/bits/thread-shared-types.h. \ + \ + There are the following cases for the kind of a mutex \ + (The mask PTHREAD_MUTEX_ELISION_FLAGS_NP covers the flags \ + PTHREAD_MUTEX_ELISION_NP and PTHREAD_MUTEX_NO_ELISION_NP where \ + only one of both flags can be set): \ + - both flags are not set: \ + This is the first lock operation for this mutex. Enable \ + elision as it is not enabled so far. \ + Note: It can happen that multiple threads are calling e.g. \ + pthread_mutex_lock at the same time as the first lock \ + operation for this mutex. Then elision is enabled for this \ + mutex by multiple threads. Storing with relaxed MO is enough \ + as all threads will store the same new value for the kind of \ + the mutex. But we have to ensure that we always use the \ + elision path regardless if this thread has enabled elision or \ + another one. \ + \ + - PTHREAD_MUTEX_ELISION_NP flag is set: \ + Elision was already enabled for this mutex by a previous lock \ + operation. See case above. Just use the elision path. \ + \ + - PTHREAD_MUTEX_NO_ELISION_NP flag is set: \ + Elision was explicitly disabled by pthread_mutexattr_settype. \ + Do not use the elision path. \ + Note: The flag PTHREAD_MUTEX_NO_ELISION_NP will never be \ + changed after mutex initialization. */ \ + int mutex_kind = atomic_load_relaxed (&((m)->__data.__kind)); \ + if ((mutex_kind & PTHREAD_MUTEX_ELISION_FLAGS_NP) == 0) \ + { \ + mutex_kind |= PTHREAD_MUTEX_ELISION_NP; \ + atomic_store_relaxed (&((m)->__data.__kind), mutex_kind); \ + } \ + if ((mutex_kind & PTHREAD_MUTEX_ELISION_NP) != 0) \ + { \ + s; \ + } \ }
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