Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756931Ab2BAUu7 (ORCPT ); Wed, 1 Feb 2012 15:50:59 -0500 Received: from mail-pw0-f46.google.com ([209.85.160.46]:33552 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756912Ab2BAUux (ORCPT ); Wed, 1 Feb 2012 15:50:53 -0500 From: Tejun Heo To: axboe@kernel.dk, vgoyal@redhat.com Cc: ctalbott@google.com, rni@google.com, linux-kernel@vger.kernel.org, Tejun Heo Subject: [PATCH 08/16] blkcg: move rcu_read_lock() outside of blkio_group get functions Date: Wed, 1 Feb 2012 12:50:21 -0800 Message-Id: <1328129429-11823-9-git-send-email-tj@kernel.org> X-Mailer: git-send-email 1.7.7.3 In-Reply-To: <1328129429-11823-1-git-send-email-tj@kernel.org> References: <1328129429-11823-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4923 Lines: 173 rcu_read_lock() in throtl_get_tb() and cfq_get_cfqg() holds onto @blkcg while looking up blkg. For API cleanup, the next patch will make the caller responsible for determining @blkcg to look blkg from and let them specify it as a parameter. Move rcu read locking out to the callers to prepare for the change. -v2: Originally this patch was described as a fix for RCU read locking bug around @blkg, which Vivek pointed out to be incorrect. It was from misunderstanding the role of rcu locking as protecting @blkg not @blkcg. Patch description updated. Signed-off-by: Tejun Heo Cc: Vivek Goyal --- block/blk-throttle.c | 18 ++++++------------ block/cfq-iosched.c | 11 +++++------ 2 files changed, 11 insertions(+), 18 deletions(-) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 3699ab4..9beaac7 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -313,25 +313,23 @@ static struct throtl_grp * throtl_get_tg(struct throtl_data *td) if (unlikely(blk_queue_bypass(q))) return NULL; - rcu_read_lock(); blkcg = task_blkio_cgroup(current); tg = throtl_find_tg(td, blkcg); - if (tg) { - rcu_read_unlock(); + if (tg) return tg; - } /* * Need to allocate a group. Allocation of group also needs allocation * of per cpu stats which in-turn takes a mutex() and can block. Hence * we need to drop rcu lock and queue_lock before we call alloc. */ - rcu_read_unlock(); spin_unlock_irq(q->queue_lock); + rcu_read_unlock(); tg = throtl_alloc_tg(td); /* Group allocated and queue is still alive. take the lock */ + rcu_read_lock(); spin_lock_irq(q->queue_lock); /* Make sure @q is still alive */ @@ -343,7 +341,6 @@ static struct throtl_grp * throtl_get_tg(struct throtl_data *td) /* * Initialize the new group. After sleeping, read the blkcg again. */ - rcu_read_lock(); blkcg = task_blkio_cgroup(current); /* @@ -354,7 +351,6 @@ static struct throtl_grp * throtl_get_tg(struct throtl_data *td) if (__tg) { kfree(tg); - rcu_read_unlock(); return __tg; } @@ -365,7 +361,6 @@ static struct throtl_grp * throtl_get_tg(struct throtl_data *td) } throtl_init_add_tg_lists(td, tg, blkcg); - rcu_read_unlock(); return tg; } @@ -1150,7 +1145,6 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio) * basic fields like stats and io rates. If a group has no rules, * just update the dispatch stats in lockless manner and return. */ - rcu_read_lock(); blkcg = task_blkio_cgroup(current); tg = throtl_find_tg(td, blkcg); @@ -1160,11 +1154,9 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio) if (tg_no_rule_group(tg, rw)) { blkiocg_update_dispatch_stats(&tg->blkg, bio->bi_size, rw, rw_is_sync(bio->bi_rw)); - rcu_read_unlock(); - goto out; + goto out_unlock_rcu; } } - rcu_read_unlock(); /* * Either group has not been allocated yet or it is not an unlimited @@ -1222,6 +1214,8 @@ queue_bio: out_unlock: spin_unlock_irq(q->queue_lock); +out_unlock_rcu: + rcu_read_unlock(); out: return throttled; } diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index f268ae4..fa60652 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1128,13 +1128,10 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd) struct cfq_group *cfqg = NULL, *__cfqg = NULL; struct request_queue *q = cfqd->queue; - rcu_read_lock(); blkcg = task_blkio_cgroup(current); cfqg = cfq_find_cfqg(cfqd, blkcg); - if (cfqg) { - rcu_read_unlock(); + if (cfqg) return cfqg; - } /* * Need to allocate a group. Allocation of group also needs allocation @@ -1164,7 +1161,6 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd) if (__cfqg) { kfree(cfqg); - rcu_read_unlock(); return __cfqg; } @@ -1172,7 +1168,6 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd) cfqg = &cfqd->root_group; cfq_init_add_cfqg_lists(cfqd, cfqg, blkcg); - rcu_read_unlock(); return cfqg; } @@ -2877,6 +2872,8 @@ cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_group *cfqg; retry: + rcu_read_lock(); + cfqg = cfq_get_cfqg(cfqd); cic = cfq_cic_lookup(cfqd, ioc); /* cic always exists here */ @@ -2892,6 +2889,7 @@ retry: cfqq = new_cfqq; new_cfqq = NULL; } else if (gfp_mask & __GFP_WAIT) { + rcu_read_unlock(); spin_unlock_irq(cfqd->queue->queue_lock); new_cfqq = kmem_cache_alloc_node(cfq_pool, gfp_mask | __GFP_ZERO, @@ -2917,6 +2915,7 @@ retry: if (new_cfqq) kmem_cache_free(cfq_pool, new_cfqq); + rcu_read_unlock(); return cfqq; } -- 1.7.7.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/