From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43628) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cdxd3-0000pX-Uq for qemu-devel@nongnu.org; Wed, 15 Feb 2017 06:20:10 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cdxd3-0007mm-1C for qemu-devel@nongnu.org; Wed, 15 Feb 2017 06:20:09 -0500 References: <20170213181244.16297-1-pbonzini@redhat.com> <20170213181244.16297-7-pbonzini@redhat.com> <20170215092341.GC26331@lemon.lan> From: Paolo Bonzini Message-ID: <1effc0aa-c050-5f09-11f8-1e3f8ced5219@redhat.com> Date: Wed, 15 Feb 2017 12:20:03 +0100 MIME-Version: 1.0 In-Reply-To: <20170215092341.GC26331@lemon.lan> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 6/6] coroutine-lock: make CoRwlock thread-safe and fair List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: qemu-devel@nongnu.org, stefanha@redhat.com, qemu-block@nongnu.org On 15/02/2017 10:23, Fam Zheng wrote: > On Mon, 02/13 19:12, Paolo Bonzini wrote: >> This adds a CoMutex around the existing CoQueue. Because the write-side > > s/CoQueue/CoRwlock/ No, I meant that CoRwlock has a CoQueue, and after this patch it is wrapped by a CoMutex too. >> @@ -375,16 +384,20 @@ void qemu_co_rwlock_unlock(CoRwlock *lock) >> qemu_co_queue_next(&lock->queue); >> } >> } >> - self->locks_held--; >> + qemu_co_mutex_unlock(&lock->mutex); >> } >> >> void qemu_co_rwlock_wrlock(CoRwlock *lock) >> { >> - Coroutine *self = qemu_coroutine_self(); >> - >> - while (lock->writer || lock->reader) { >> - qemu_co_queue_wait(&lock->queue, NULL); >> + qemu_co_mutex_lock(&lock->mutex); >> + lock->pending_writer++; >> + while (lock->reader) { >> + qemu_co_queue_wait(&lock->queue, &lock->mutex); >> } >> - lock->writer = true; >> - self->locks_held++; >> + lock->pending_writer--; >> + >> + /* The rest of the write-side critical section is run with >> + * the mutex taken, so that lock->reader remains zero. >> + * There is no need to update self->locks_held. >> + */ > > But is it still better to update self->locks_held anyway for the > 'assert(!co->locks_held)' in qemu_coroutine_enter? Or is the same thing checked > elsewhere? self->locks_held is already incremented by the qemu_co_mutex_lock call at the beginning of qemu_co_rwlock_wrlock. It is then decremented in qemu_co_rwlock_unlock. For the read side, rdlock _unlocks_ lock->mutex before returning, so self->locks_held must be incremented by rdlock and decremented by unlock. Paolo