File force-elision-race.patch of Package glibc.20354
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; \
+ } \
}
