diff options
| author | riastradh <riastradh@NetBSD.org> | 2022-02-11 21:40:58 +0000 |
|---|---|---|
| committer | riastradh <riastradh@NetBSD.org> | 2022-02-11 21:40:58 +0000 |
| commit | cb5cc3d8ac194632cef3250fd4806d0f7c2e1406 (patch) | |
| tree | 26fcb95b2a765fe708cf6684d9907bf510e5f053 /lib/libpthread | |
| parent | ee74c09aab4aef92718eefe7060b28135fb26dec (diff) | |
libpthread: Fix membars around rwlocks.
1. After loading self->pt_rwlocked, membar_enter() must not be
conditional on PTHREAD__ATOMIC_IS_MEMBAR because there is no
atomic r/m/w operation here which could imply the acquire barrier.
(This should maybe just be a load-acquire operation, but we don't
have atomic_load_acquire in userland at the moment -- TBD.)
2. Before storing thread->pt_rwlocked, must issue membar_exit() so
that this is a store-release operation -- except if we had just
done an atomic r/m/w and PTHREAD__ATOMIC_IS_MEMBAR is set, in
which case it can be elided.
The second membar_exit() added here might be safely hoisted out of
the loop but I'm not sure -- needs more analysis to prove that
would be safe.
Diffstat (limited to 'lib/libpthread')
| -rw-r--r-- | lib/libpthread/pthread_rwlock.c | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/lib/libpthread/pthread_rwlock.c b/lib/libpthread/pthread_rwlock.c index 79f8d28ae3f..8d452d3dbc6 100644 --- a/lib/libpthread/pthread_rwlock.c +++ b/lib/libpthread/pthread_rwlock.c @@ -1,4 +1,4 @@ -/* $NetBSD: pthread_rwlock.c,v 1.42 2020/06/02 00:29:53 joerg Exp $ */ +/* $NetBSD: pthread_rwlock.c,v 1.43 2022/02/11 21:40:58 riastradh Exp $ */ /*- * Copyright (c) 2002, 2006, 2007, 2008, 2020 The NetBSD Foundation, Inc. @@ -30,7 +30,7 @@ */ #include <sys/cdefs.h> -__RCSID("$NetBSD: pthread_rwlock.c,v 1.42 2020/06/02 00:29:53 joerg Exp $"); +__RCSID("$NetBSD: pthread_rwlock.c,v 1.43 2022/02/11 21:40:58 riastradh Exp $"); #include <sys/types.h> #include <sys/lwpctl.h> @@ -228,9 +228,7 @@ pthread__rwlock_rdlock(pthread_rwlock_t *ptr, const struct timespec *ts) /* Did we get the lock? */ if (self->pt_rwlocked == _RW_LOCKED) { -#ifndef PTHREAD__ATOMIC_IS_MEMBAR membar_enter(); -#endif return 0; } if (error != 0) @@ -352,9 +350,7 @@ pthread__rwlock_wrlock(pthread_rwlock_t *ptr, const struct timespec *ts) /* Did we get the lock? */ if (self->pt_rwlocked == _RW_LOCKED) { -#ifndef PTHREAD__ATOMIC_IS_MEMBAR membar_enter(); -#endif return 0; } if (error != 0) @@ -526,6 +522,9 @@ pthread_rwlock_unlock(pthread_rwlock_t *ptr) * by the writer that we are about to wake. */ (void)atomic_swap_ptr(&ptr->ptr_owner, (void *)new); +#ifndef PTHREAD__ATOMIC_IS_MEMBAR + membar_exit(); +#endif /* Wake the writer. */ thread->pt_rwlocked = _RW_LOCKED; @@ -543,6 +542,7 @@ pthread_rwlock_unlock(pthread_rwlock_t *ptr) if (thread->pt_sleepobj == NULL) continue; new += RW_READ_INCR; + membar_exit(); thread->pt_rwlocked = _RW_LOCKED; } |
