blkcg: convert blkg_lookup_create to find closest blkg
There are several scenarios where blkg_lookup_create can fail. Examples include the blkcg dying, request_queue is dying, or simply being OOM. At the end of the day, most handle this by simply falling back to the q->root_blkg and calling it a day. This patch implements the notion of closest blkg. During blkg_lookup_create, if it fails to create, return the closest blkg found or the q->root_blkg. blkg_try_get_closest is introduced and used during association so a bio is always attached to a blkg. Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Dennis Zhou <dennisszhou@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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17
block/bio.c
17
block/bio.c
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@ -2007,21 +2007,24 @@ int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css)
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EXPORT_SYMBOL_GPL(bio_associate_blkcg);
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/**
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* bio_associate_blkg - associate a bio with the specified blkg
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* bio_associate_blkg - associate a bio with the a blkg
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* @bio: target bio
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* @blkg: the blkg to associate
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*
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* Associate @bio with the blkg specified by @blkg. This is the queue specific
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* blkcg information associated with the @bio, a reference will be taken on the
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* @blkg and will be freed when the bio is freed.
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* This tries to associate @bio with the specified blkg. Association failure
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* is handled by walking up the blkg tree. Therefore, the blkg associated can
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* be anything between @blkg and the root_blkg. This situation only happens
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* when a cgroup is dying and then the remaining bios will spill to the closest
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* alive blkg.
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*
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* A reference will be taken on the @blkg and will be released when @bio is
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* freed.
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*/
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int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg)
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{
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if (unlikely(bio->bi_blkg))
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return -EBUSY;
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if (!blkg_try_get(blkg))
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return -ENODEV;
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bio->bi_blkg = blkg;
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bio->bi_blkg = blkg_try_get_closest(blkg);
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return 0;
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}
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@ -268,9 +268,8 @@ err_free_blkg:
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* that all non-root blkg's have access to the parent blkg. This function
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* should be called under RCU read lock and @q->queue_lock.
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*
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* Returns pointer to the looked up or created blkg on success, ERR_PTR()
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* value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not
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* dead and bypassing, returns ERR_PTR(-EBUSY).
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* Returns the blkg or the closest blkg if blkg_create fails as it walks
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* down from root.
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*/
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struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
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struct request_queue *q)
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@ -285,7 +284,7 @@ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
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* we shouldn't allow anything to go through for a bypassing queue.
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*/
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if (unlikely(blk_queue_bypass(q)))
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return ERR_PTR(blk_queue_dying(q) ? -ENODEV : -EBUSY);
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return q->root_blkg;
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blkg = __blkg_lookup(blkcg, q, true);
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if (blkg)
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@ -293,19 +292,29 @@ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
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/*
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* Create blkgs walking down from blkcg_root to @blkcg, so that all
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* non-root blkgs have access to their parents.
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* non-root blkgs have access to their parents. Returns the closest
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* blkg to the intended blkg should blkg_create() fail.
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*/
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while (true) {
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struct blkcg *pos = blkcg;
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struct blkcg *parent = blkcg_parent(blkcg);
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struct blkcg_gq *ret_blkg = q->root_blkg;
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while (parent && !__blkg_lookup(parent, q, false)) {
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while (parent) {
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blkg = __blkg_lookup(parent, q, false);
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if (blkg) {
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/* remember closest blkg */
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ret_blkg = blkg;
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break;
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}
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pos = parent;
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parent = blkcg_parent(parent);
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}
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blkg = blkg_create(pos, q, NULL);
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if (pos == blkcg || IS_ERR(blkg))
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if (IS_ERR(blkg))
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return ret_blkg;
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if (pos == blkcg)
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return blkg;
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}
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}
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@ -549,6 +549,20 @@ static inline struct blkcg_gq *blkg_try_get(struct blkcg_gq *blkg)
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return NULL;
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}
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/**
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* blkg_try_get_closest - try and get a blkg ref on the closet blkg
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* @blkg: blkg to get
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*
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* This walks up the blkg tree to find the closest non-dying blkg and returns
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* the blkg that it did association with as it may not be the passed in blkg.
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*/
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static inline struct blkcg_gq *blkg_try_get_closest(struct blkcg_gq *blkg)
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{
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while (!atomic_inc_not_zero(&blkg->refcnt))
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blkg = blkg->parent;
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return blkg;
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}
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void __blkg_release_rcu(struct rcu_head *rcu);
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