From patchwork Mon Jul 27 02:24:18 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wen Congyang X-Patchwork-Id: 500189 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id C712C140324 for ; Mon, 27 Jul 2015 12:24:49 +1000 (AEST) Received: from localhost ([::1]:51315 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZJY5s-0001Oo-LC for incoming@patchwork.ozlabs.org; Sun, 26 Jul 2015 22:24:44 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49871) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZJY5e-000184-FR for qemu-devel@nongnu.org; Sun, 26 Jul 2015 22:24:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZJY5a-0003S6-Bu for qemu-devel@nongnu.org; Sun, 26 Jul 2015 22:24:30 -0400 Received: from [59.151.112.132] (port=53169 helo=heian.cn.fujitsu.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZJY5X-0003M0-Oq for qemu-devel@nongnu.org; Sun, 26 Jul 2015 22:24:26 -0400 X-IronPort-AV: E=Sophos;i="5.15,520,1432569600"; d="scan'208";a="98910683" Received: from unknown (HELO edo.cn.fujitsu.com) ([10.167.33.5]) by heian.cn.fujitsu.com with ESMTP; 27 Jul 2015 10:27:51 +0800 Received: from G08CNEXCHPEKD02.g08.fujitsu.local (localhost.localdomain [127.0.0.1]) by edo.cn.fujitsu.com (8.14.3/8.13.1) with ESMTP id t6R2MO8S019587; Mon, 27 Jul 2015 10:22:24 +0800 Received: from [10.167.226.52] (10.167.226.52) by G08CNEXCHPEKD02.g08.fujitsu.local (10.167.33.89) with Microsoft SMTP Server id 14.3.181.6; Mon, 27 Jul 2015 10:24:14 +0800 To: qemu-devl , Paolo Bonzini From: Wen Congyang Message-ID: <55B59652.4090503@cn.fujitsu.com> Date: Mon, 27 Jul 2015 10:24:18 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 X-Originating-IP: [10.167.226.52] X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 59.151.112.132 Subject: [Qemu-devel] [PATCH for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org If rcu_(un)register_thread() is called together with synchronize_rcu(), it will wait for the synchronize_rcu() to finish. But when synchronize_rcu() waits for some events, we can modify the list registry. We also use the lock rcu_gp_lock to assume that synchronize_rcu() isn't executed in more than one thread at the same time. Add a new mutex lock rcu_sync_lock to assume it and rename rcu_gp_lock to rcu_registry_lock. Release rcu_registry_lock when synchronize_rcu() waits for some events. Signed-off-by: Wen Congyang --- util/rcu.c | 36 +++++++++++++++++++++++------------- 1 file changed, 23 insertions(+), 13 deletions(-) diff --git a/util/rcu.c b/util/rcu.c index cdcad67..18c5792 100644 --- a/util/rcu.c +++ b/util/rcu.c @@ -47,7 +47,8 @@ unsigned long rcu_gp_ctr = RCU_GP_LOCKED; QemuEvent rcu_gp_event; -static QemuMutex rcu_gp_lock; +static QemuMutex rcu_registry_lock; +static QemuMutex rcu_sync_lock; /* * Check whether a quiescent state was crossed between the beginning of @@ -66,7 +67,7 @@ static inline int rcu_gp_ongoing(unsigned long *ctr) */ __thread struct rcu_reader_data rcu_reader; -/* Protected by rcu_gp_lock. */ +/* Protected by rcu_registry_lock. */ typedef QLIST_HEAD(, rcu_reader_data) ThreadList; static ThreadList registry = QLIST_HEAD_INITIALIZER(registry); @@ -114,10 +115,14 @@ static void wait_for_readers(void) break; } - /* Wait for one thread to report a quiescent state and - * try again. + /* Wait for one thread to report a quiescent state and try again. + * Release rcu_registry_lock, so rcu_(un)register_thread() doesn't + * wait too much time. Note: rcu_unregister_thread() may remove + * the node from qsreaders. That's a bit tricky, but it should work. */ + qemu_mutex_unlock(&rcu_registry_lock); qemu_event_wait(&rcu_gp_event); + qemu_mutex_lock(&rcu_registry_lock); } /* put back the reader list in the registry */ @@ -126,7 +131,8 @@ static void wait_for_readers(void) void synchronize_rcu(void) { - qemu_mutex_lock(&rcu_gp_lock); + qemu_mutex_lock(&rcu_sync_lock); + qemu_mutex_lock(&rcu_registry_lock); if (!QLIST_EMPTY(®istry)) { /* In either case, the atomic_mb_set below blocks stores that free @@ -149,7 +155,8 @@ void synchronize_rcu(void) wait_for_readers(); } - qemu_mutex_unlock(&rcu_gp_lock); + qemu_mutex_unlock(&rcu_registry_lock); + qemu_mutex_unlock(&rcu_sync_lock); } @@ -273,23 +280,24 @@ void call_rcu1(struct rcu_head *node, void (*func)(struct rcu_head *node)) void rcu_register_thread(void) { assert(rcu_reader.ctr == 0); - qemu_mutex_lock(&rcu_gp_lock); + qemu_mutex_lock(&rcu_registry_lock); QLIST_INSERT_HEAD(®istry, &rcu_reader, node); - qemu_mutex_unlock(&rcu_gp_lock); + qemu_mutex_unlock(&rcu_registry_lock); } void rcu_unregister_thread(void) { - qemu_mutex_lock(&rcu_gp_lock); + qemu_mutex_lock(&rcu_registry_lock); QLIST_REMOVE(&rcu_reader, node); - qemu_mutex_unlock(&rcu_gp_lock); + qemu_mutex_unlock(&rcu_registry_lock); } static void rcu_init_complete(void) { QemuThread thread; - qemu_mutex_init(&rcu_gp_lock); + qemu_mutex_init(&rcu_registry_lock); + qemu_mutex_init(&rcu_sync_lock); qemu_event_init(&rcu_gp_event, true); qemu_event_init(&rcu_call_ready_event, false); @@ -306,12 +314,14 @@ static void rcu_init_complete(void) #ifdef CONFIG_POSIX static void rcu_init_lock(void) { - qemu_mutex_lock(&rcu_gp_lock); + qemu_mutex_lock(&rcu_sync_lock); + qemu_mutex_lock(&rcu_registry_lock); } static void rcu_init_unlock(void) { - qemu_mutex_unlock(&rcu_gp_lock); + qemu_mutex_unlock(&rcu_registry_lock); + qemu_mutex_unlock(&rcu_sync_lock); } #endif