From owner-svn-src-all@FreeBSD.ORG Wed Sep 30 13:26:31 2009 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B82181065672; Wed, 30 Sep 2009 13:26:31 +0000 (UTC) (envelope-from attilio@FreeBSD.org) Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:4f8:fff6::2c]) by mx1.freebsd.org (Postfix) with ESMTP id A558C8FC14; Wed, 30 Sep 2009 13:26:31 +0000 (UTC) Received: from svn.freebsd.org (localhost [127.0.0.1]) by svn.freebsd.org (8.14.3/8.14.3) with ESMTP id n8UDQVuK016401; Wed, 30 Sep 2009 13:26:31 GMT (envelope-from attilio@svn.freebsd.org) Received: (from attilio@localhost) by svn.freebsd.org (8.14.3/8.14.3/Submit) id n8UDQVB1016396; Wed, 30 Sep 2009 13:26:31 GMT (envelope-from attilio@svn.freebsd.org) Message-Id: <200909301326.n8UDQVB1016396@svn.freebsd.org> From: Attilio Rao Date: Wed, 30 Sep 2009 13:26:31 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org X-SVN-Group: head MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Cc: Subject: svn commit: r197643 - in head/sys: kern sys X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 30 Sep 2009 13:26:31 -0000 Author: attilio Date: Wed Sep 30 13:26:31 2009 New Revision: 197643 URL: http://svn.freebsd.org/changeset/base/197643 Log: When releasing a read/shared lock we need to use a write memory barrier in order to avoid, on architectures which doesn't have strong ordered writes, CPU instructions reordering. Diagnosed by: fabio Reviewed by: jhb Tested by: Giovanni Trematerra Modified: head/sys/kern/kern_rwlock.c head/sys/kern/kern_sx.c head/sys/sys/rwlock.h head/sys/sys/sx.h Modified: head/sys/kern/kern_rwlock.c ============================================================================== --- head/sys/kern/kern_rwlock.c Wed Sep 30 12:53:21 2009 (r197642) +++ head/sys/kern/kern_rwlock.c Wed Sep 30 13:26:31 2009 (r197643) @@ -541,7 +541,7 @@ _rw_runlock(struct rwlock *rw, const cha */ x = rw->rw_lock; if (RW_READERS(x) > 1) { - if (atomic_cmpset_ptr(&rw->rw_lock, x, + if (atomic_cmpset_rel_ptr(&rw->rw_lock, x, x - RW_ONE_READER)) { if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR4(KTR_LOCK, @@ -559,7 +559,8 @@ _rw_runlock(struct rwlock *rw, const cha if (!(x & RW_LOCK_WAITERS)) { MPASS((x & ~RW_LOCK_WRITE_SPINNER) == RW_READERS_LOCK(1)); - if (atomic_cmpset_ptr(&rw->rw_lock, x, RW_UNLOCKED)) { + if (atomic_cmpset_rel_ptr(&rw->rw_lock, x, + RW_UNLOCKED)) { if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p last succeeded", __func__, rw); @@ -597,7 +598,7 @@ _rw_runlock(struct rwlock *rw, const cha x |= (v & RW_LOCK_READ_WAITERS); } else queue = TS_SHARED_QUEUE; - if (!atomic_cmpset_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v, + if (!atomic_cmpset_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v, x)) { turnstile_chain_unlock(&rw->lock_object); continue; Modified: head/sys/kern/kern_sx.c ============================================================================== --- head/sys/kern/kern_sx.c Wed Sep 30 12:53:21 2009 (r197642) +++ head/sys/kern/kern_sx.c Wed Sep 30 13:26:31 2009 (r197643) @@ -931,7 +931,7 @@ _sx_sunlock_hard(struct sx *sx, const ch * so, just drop one and return. */ if (SX_SHARERS(x) > 1) { - if (atomic_cmpset_ptr(&sx->sx_lock, x, + if (atomic_cmpset_rel_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER)) { if (LOCK_LOG_TEST(&sx->lock_object, 0)) CTR4(KTR_LOCK, @@ -949,8 +949,8 @@ _sx_sunlock_hard(struct sx *sx, const ch */ if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { MPASS(x == SX_SHARERS_LOCK(1)); - if (atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1), - SX_LOCK_UNLOCKED)) { + if (atomic_cmpset_rel_ptr(&sx->sx_lock, + SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) { if (LOCK_LOG_TEST(&sx->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p last succeeded", __func__, sx); @@ -973,7 +973,7 @@ _sx_sunlock_hard(struct sx *sx, const ch * Note that the state of the lock could have changed, * so if it fails loop back and retry. */ - if (!atomic_cmpset_ptr(&sx->sx_lock, + if (!atomic_cmpset_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS, SX_LOCK_UNLOCKED)) { sleepq_release(&sx->lock_object); Modified: head/sys/sys/rwlock.h ============================================================================== --- head/sys/sys/rwlock.h Wed Sep 30 12:53:21 2009 (r197642) +++ head/sys/sys/rwlock.h Wed Sep 30 13:26:31 2009 (r197643) @@ -55,13 +55,6 @@ * * When the lock is not locked by any thread, it is encoded as a read lock * with zero waiters. - * - * A note about memory barriers. Write locks need to use the same memory - * barriers as mutexes: _acq when acquiring a write lock and _rel when - * releasing a write lock. Read locks also need to use an _acq barrier when - * acquiring a read lock. However, since read locks do not update any - * locked data (modulo bugs of course), no memory barrier is needed when - * releasing a read lock. */ #define RW_LOCK_READ 0x01 Modified: head/sys/sys/sx.h ============================================================================== --- head/sys/sys/sx.h Wed Sep 30 12:53:21 2009 (r197642) +++ head/sys/sys/sx.h Wed Sep 30 13:26:31 2009 (r197643) @@ -63,13 +63,6 @@ * * When the lock is not locked by any thread, it is encoded as a * shared lock with zero waiters. - * - * A note about memory barriers. Exclusive locks need to use the same - * memory barriers as mutexes: _acq when acquiring an exclusive lock - * and _rel when releasing an exclusive lock. On the other side, - * shared lock needs to use an _acq barrier when acquiring the lock - * but, since they don't update any locked data, no memory barrier is - * needed when releasing a shared lock. */ #define SX_LOCK_SHARED 0x01 @@ -200,7 +193,7 @@ __sx_sunlock(struct sx *sx, const char * uintptr_t x = sx->sx_lock; if (x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS) || - !atomic_cmpset_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER)) + !atomic_cmpset_rel_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER)) _sx_sunlock_hard(sx, file, line); }