From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: [PATCH 06/11] blkcg: make sure blkg_lookup() returns %NULL if @q is bypassing Date: Fri, 13 Apr 2012 13:11:30 -0700 Message-ID: <1334347895-6268-7-git-send-email-tj@kernel.org> References: <1334347895-6268-1-git-send-email-tj@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1334347895-6268-1-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org Cc: ctalbott-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, rni-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Tejun Heo , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org List-Id: containers.vger.kernel.org Currently, blkg_lookup() doesn't check @q bypass state. This patch updates blk_queue_bypass_start() to do synchronize_rcu() before returning and updates blkg_lookup() to check blk_queue_bypass() and return %NULL if bypassing. This ensures blkg_lookup() returns %NULL if @q is bypassing. This is to guarantee that nobody is accessing policy data while @q is bypassing, which is necessary to allow replacing blkio_cgroup->pd[] in place on policy [de]activation. v2: Added more comments explaining bypass guarantees as suggested by Vivek. Signed-off-by: Tejun Heo Cc: Vivek Goyal --- block/blk-cgroup.c | 50 +++++++++++++++++++++++++++++++++----------------- block/blk-core.c | 5 ++++- 2 files changed, 37 insertions(+), 18 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index f6581a0..d6e4555 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -137,6 +137,38 @@ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg, return blkg; } +static struct blkio_group *__blkg_lookup(struct blkio_cgroup *blkcg, + struct request_queue *q) +{ + struct blkio_group *blkg; + struct hlist_node *n; + + hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) + if (blkg->q == q) + return blkg; + return NULL; +} + +/** + * blkg_lookup - lookup blkg for the specified blkcg - q pair + * @blkcg: blkcg of interest + * @q: request_queue of interest + * + * Lookup blkg for the @blkcg - @q pair. This function should be called + * under RCU read lock and is guaranteed to return %NULL if @q is bypassing + * - see blk_queue_bypass_start() for details. + */ +struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg, + struct request_queue *q) +{ + WARN_ON_ONCE(!rcu_read_lock_held()); + + if (unlikely(blk_queue_bypass(q))) + return NULL; + return __blkg_lookup(blkcg, q); +} +EXPORT_SYMBOL_GPL(blkg_lookup); + struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, struct request_queue *q, bool for_root) @@ -150,13 +182,11 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, /* * This could be the first entry point of blkcg implementation and * we shouldn't allow anything to go through for a bypassing queue. - * The following can be removed if blkg lookup is guaranteed to - * fail on a bypassing queue. */ if (unlikely(blk_queue_bypass(q)) && !for_root) return ERR_PTR(blk_queue_dead(q) ? -EINVAL : -EBUSY); - blkg = blkg_lookup(blkcg, q); + blkg = __blkg_lookup(blkcg, q); if (blkg) return blkg; @@ -185,20 +215,6 @@ out: } EXPORT_SYMBOL_GPL(blkg_lookup_create); -/* called under rcu_read_lock(). */ -struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg, - struct request_queue *q) -{ - struct blkio_group *blkg; - struct hlist_node *n; - - hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) - if (blkg->q == q) - return blkg; - return NULL; -} -EXPORT_SYMBOL_GPL(blkg_lookup); - static void blkg_destroy(struct blkio_group *blkg) { struct request_queue *q = blkg->q; diff --git a/block/blk-core.c b/block/blk-core.c index 991c1d6..a4b3eaf 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -416,7 +416,8 @@ void blk_drain_queue(struct request_queue *q, bool drain_all) * In bypass mode, only the dispatch FIFO queue of @q is used. This * function makes @q enter bypass mode and drains all requests which were * throttled or issued before. On return, it's guaranteed that no request - * is being throttled or has ELVPRIV set. + * is being throttled or has ELVPRIV set and blk_queue_bypass() %true + * inside queue or RCU read lock. */ void blk_queue_bypass_start(struct request_queue *q) { @@ -426,6 +427,8 @@ void blk_queue_bypass_start(struct request_queue *q) spin_unlock_irq(q->queue_lock); blk_drain_queue(q, false); + /* ensure blk_queue_bypass() is %true inside RCU read lock */ + synchronize_rcu(); } EXPORT_SYMBOL_GPL(blk_queue_bypass_start); -- 1.7.7.3 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932208Ab2DMUL7 (ORCPT ); Fri, 13 Apr 2012 16:11:59 -0400 Received: from mail-pz0-f52.google.com ([209.85.210.52]:46760 "EHLO mail-pz0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932161Ab2DMULz (ORCPT ); Fri, 13 Apr 2012 16:11:55 -0400 From: Tejun Heo To: axboe@kernel.dk Cc: vgoyal@redhat.com, ctalbott@google.com, rni@google.com, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, containers@lists.linux-foundation.org, Tejun Heo Subject: [PATCH 06/11] blkcg: make sure blkg_lookup() returns %NULL if @q is bypassing Date: Fri, 13 Apr 2012 13:11:30 -0700 Message-Id: <1334347895-6268-7-git-send-email-tj@kernel.org> X-Mailer: git-send-email 1.7.7.3 In-Reply-To: <1334347895-6268-1-git-send-email-tj@kernel.org> References: <1334347895-6268-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently, blkg_lookup() doesn't check @q bypass state. This patch updates blk_queue_bypass_start() to do synchronize_rcu() before returning and updates blkg_lookup() to check blk_queue_bypass() and return %NULL if bypassing. This ensures blkg_lookup() returns %NULL if @q is bypassing. This is to guarantee that nobody is accessing policy data while @q is bypassing, which is necessary to allow replacing blkio_cgroup->pd[] in place on policy [de]activation. v2: Added more comments explaining bypass guarantees as suggested by Vivek. Signed-off-by: Tejun Heo Cc: Vivek Goyal --- block/blk-cgroup.c | 50 +++++++++++++++++++++++++++++++++----------------- block/blk-core.c | 5 ++++- 2 files changed, 37 insertions(+), 18 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index f6581a0..d6e4555 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -137,6 +137,38 @@ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg, return blkg; } +static struct blkio_group *__blkg_lookup(struct blkio_cgroup *blkcg, + struct request_queue *q) +{ + struct blkio_group *blkg; + struct hlist_node *n; + + hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) + if (blkg->q == q) + return blkg; + return NULL; +} + +/** + * blkg_lookup - lookup blkg for the specified blkcg - q pair + * @blkcg: blkcg of interest + * @q: request_queue of interest + * + * Lookup blkg for the @blkcg - @q pair. This function should be called + * under RCU read lock and is guaranteed to return %NULL if @q is bypassing + * - see blk_queue_bypass_start() for details. + */ +struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg, + struct request_queue *q) +{ + WARN_ON_ONCE(!rcu_read_lock_held()); + + if (unlikely(blk_queue_bypass(q))) + return NULL; + return __blkg_lookup(blkcg, q); +} +EXPORT_SYMBOL_GPL(blkg_lookup); + struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, struct request_queue *q, bool for_root) @@ -150,13 +182,11 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, /* * This could be the first entry point of blkcg implementation and * we shouldn't allow anything to go through for a bypassing queue. - * The following can be removed if blkg lookup is guaranteed to - * fail on a bypassing queue. */ if (unlikely(blk_queue_bypass(q)) && !for_root) return ERR_PTR(blk_queue_dead(q) ? -EINVAL : -EBUSY); - blkg = blkg_lookup(blkcg, q); + blkg = __blkg_lookup(blkcg, q); if (blkg) return blkg; @@ -185,20 +215,6 @@ out: } EXPORT_SYMBOL_GPL(blkg_lookup_create); -/* called under rcu_read_lock(). */ -struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg, - struct request_queue *q) -{ - struct blkio_group *blkg; - struct hlist_node *n; - - hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) - if (blkg->q == q) - return blkg; - return NULL; -} -EXPORT_SYMBOL_GPL(blkg_lookup); - static void blkg_destroy(struct blkio_group *blkg) { struct request_queue *q = blkg->q; diff --git a/block/blk-core.c b/block/blk-core.c index 991c1d6..a4b3eaf 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -416,7 +416,8 @@ void blk_drain_queue(struct request_queue *q, bool drain_all) * In bypass mode, only the dispatch FIFO queue of @q is used. This * function makes @q enter bypass mode and drains all requests which were * throttled or issued before. On return, it's guaranteed that no request - * is being throttled or has ELVPRIV set. + * is being throttled or has ELVPRIV set and blk_queue_bypass() %true + * inside queue or RCU read lock. */ void blk_queue_bypass_start(struct request_queue *q) { @@ -426,6 +427,8 @@ void blk_queue_bypass_start(struct request_queue *q) spin_unlock_irq(q->queue_lock); blk_drain_queue(q, false); + /* ensure blk_queue_bypass() is %true inside RCU read lock */ + synchronize_rcu(); } EXPORT_SYMBOL_GPL(blk_queue_bypass_start); -- 1.7.7.3