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locks: make trylock routines check for 'unowned' value

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Since fcmpset can fail without lock contention e.g. on arm, it was possible
to get spurious failures when the caller was expecting the primitive to succeed.

Reported by:	mmel
This commit is contained in:
Mateusz Guzik 2017-02-19 16:28:46 +00:00
parent 30545786bb
commit b247fd395d
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=313944
3 changed files with 27 additions and 12 deletions
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17
sys/kern/kern_mutex.c
View File

@ -402,16 +402,21 @@ _mtx_trylock_flags_(volatile uintptr_t *c, int opts, const char *file, int line)
rval = 1;
recursed = false;
v = MTX_UNOWNED;
if (!_mtx_obtain_lock_fetch(m, &v, tid)) {
for (;;) {
if (_mtx_obtain_lock_fetch(m, &v, tid))
break;
if (v == MTX_UNOWNED)
continue;
if (v == tid &&
((m->lock_object.lo_flags & LO_RECURSABLE) != 0 ||
(opts & MTX_RECURSE) != 0)) {
m->mtx_recurse++;
atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
recursed = true;
} else {
rval = 0;
m->mtx_recurse++;
atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
recursed = true;
break;
}
rval = 0;
break;
}
opts &= ~MTX_RECURSE;

11
sys/kern/kern_rwlock.c
View File

@ -314,13 +314,18 @@ __rw_try_wlock(volatile uintptr_t *c, const char *file, int line)
rval = 1;
recursed = false;
v = RW_UNLOCKED;
if (!atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid)) {
for (;;) {
if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid))
break;
if (v == RW_UNLOCKED)
continue;
if (v == tid && (rw->lock_object.lo_flags & LO_RECURSABLE)) {
rw->rw_recurse++;
atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
} else {
rval = 0;
break;
}
rval = 0;
break;
}
LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line);

11
sys/kern/kern_sx.c
View File

@ -341,13 +341,18 @@ sx_try_xlock_(struct sx *sx, const char *file, int line)
rval = 1;
recursed = false;
x = SX_LOCK_UNLOCKED;
if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) {
for (;;) {
if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
break;
if (x == SX_LOCK_UNLOCKED)
continue;
if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) {
sx->sx_recurse++;
atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
} else {
rval = 0;
break;
}
rval = 0;
break;
}
LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);