blkcg: move bulk of blkcg_gq release operations to the RCU callback
Currently, when the last reference of a blkcg_gq is put, all then release operations sans the actual freeing happen directly in blkg_put(). As blkg_put() may be called under queue_lock, all pd_exit_fn()s may be too. This makes it impossible for pd_exit_fn()s to use del_timer_sync() on timers which grab the queue_lock which is an irq-safe lock due to the deadlock possibility described in the comment on top of del_timer_sync(). This can be easily avoided by perfoming the release operations in the RCU callback instead of directly from blkg_put(). This patch moves the blkcg_gq release operations to the RCU callback. As this leaves __blkg_release() with only call_rcu() invocation, blkg_rcu_free() is renamed to __blkg_release_rcu(), exported and call_rcu() invocation is now done directly from blkg_put() instead of going through __blkg_release() which is removed. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Vivek Goyal <vgoyal@redhat.com>
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db61367038
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2a4fd070ee
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@ -369,13 +369,17 @@ static void blkg_destroy_all(struct request_queue *q)
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q->root_rl.blkg = NULL;
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}
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static void blkg_rcu_free(struct rcu_head *rcu_head)
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{
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blkg_free(container_of(rcu_head, struct blkcg_gq, rcu_head));
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}
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void __blkg_release(struct blkcg_gq *blkg)
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/*
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* A group is RCU protected, but having an rcu lock does not mean that one
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* can access all the fields of blkg and assume these are valid. For
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* example, don't try to follow throtl_data and request queue links.
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*
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* Having a reference to blkg under an rcu allows accesses to only values
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* local to groups like group stats and group rate limits.
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*/
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void __blkg_release_rcu(struct rcu_head *rcu_head)
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{
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struct blkcg_gq *blkg = container_of(rcu_head, struct blkcg_gq, rcu_head);
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int i;
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/* tell policies that this one is being freed */
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@ -388,21 +392,15 @@ void __blkg_release(struct blkcg_gq *blkg)
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/* release the blkcg and parent blkg refs this blkg has been holding */
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css_put(&blkg->blkcg->css);
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if (blkg->parent)
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if (blkg->parent) {
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spin_lock_irq(blkg->q->queue_lock);
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blkg_put(blkg->parent);
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spin_unlock_irq(blkg->q->queue_lock);
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}
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/*
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* A group is freed in rcu manner. But having an rcu lock does not
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* mean that one can access all the fields of blkg and assume these
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* are valid. For example, don't try to follow throtl_data and
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* request queue links.
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*
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* Having a reference to blkg under an rcu allows acess to only
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* values local to groups like group stats and group rate limits
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*/
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call_rcu(&blkg->rcu_head, blkg_rcu_free);
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blkg_free(blkg);
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}
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EXPORT_SYMBOL_GPL(__blkg_release);
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EXPORT_SYMBOL_GPL(__blkg_release_rcu);
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/*
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* The next function used by blk_queue_for_each_rl(). It's a bit tricky
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@ -266,7 +266,7 @@ static inline void blkg_get(struct blkcg_gq *blkg)
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blkg->refcnt++;
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}
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void __blkg_release(struct blkcg_gq *blkg);
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void __blkg_release_rcu(struct rcu_head *rcu);
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/**
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* blkg_put - put a blkg reference
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@ -279,7 +279,7 @@ static inline void blkg_put(struct blkcg_gq *blkg)
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lockdep_assert_held(blkg->q->queue_lock);
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WARN_ON_ONCE(blkg->refcnt <= 0);
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if (!--blkg->refcnt)
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__blkg_release(blkg);
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call_rcu(&blkg->rcu_head, __blkg_release_rcu);
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}
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struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg, struct request_queue *q,
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