The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4e54a2493e582361adc3bfbf06c7d50d19d18837 Mon Sep 17 00:00:00 2001 From: Jan Kara jack@suse.cz Date: Fri, 1 Apr 2022 12:27:49 +0200 Subject: [PATCH] bfq: Get rid of __bio_blkcg() usage

BFQ usage of __bio_blkcg() is a relict from the past. Furthermore if bio would not be associated with any blkcg, the usage of __bio_blkcg() in BFQ is prone to races with the task being migrated between cgroups as __bio_blkcg() calls at different places could return different blkcgs.

Convert BFQ to the new situation where bio->bi_blkg is initialized in bio_set_dev() and thus practically always valid. This allows us to save blkcg_gq lookup and noticeably simplify the code.

CC: stable@vger.kernel.org Fixes: 0fe061b9f03c ("blkcg: fix ref count issue with bio_blkcg() using task_css") Tested-by: "yukuai (C)" yukuai3@huawei.com Signed-off-by: Jan Kara jack@suse.cz Reviewed-by: Christoph Hellwig hch@lst.de Link: https://lore.kernel.org/r/20220401102752.8599-8-jack@suse.cz Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c index 879380c2bc7e..32d2c2a47480 100644 --- a/block/bfq-cgroup.c +++ b/block/bfq-cgroup.c @@ -586,27 +586,11 @@ static void bfq_group_set_parent(struct bfq_group *bfqg, entity->sched_data = &parent->sched_data; }

-static struct bfq_group *bfq_lookup_bfqg(struct bfq_data *bfqd, - struct blkcg *blkcg) +static void bfq_link_bfqg(struct bfq_data *bfqd, struct bfq_group *bfqg) { - struct blkcg_gq *blkg; - - blkg = blkg_lookup(blkcg, bfqd->queue); - if (likely(blkg)) - return blkg_to_bfqg(blkg); - return NULL; -} - -struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd, - struct blkcg *blkcg) -{ - struct bfq_group *bfqg, *parent; + struct bfq_group *parent; struct bfq_entity *entity;

- bfqg = bfq_lookup_bfqg(bfqd, blkcg); - if (unlikely(!bfqg)) - return NULL; - /* * Update chain of bfq_groups as we might be handling a leaf group * which, along with some of its relatives, has not been hooked yet @@ -623,8 +607,15 @@ struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd, bfq_group_set_parent(curr_bfqg, parent); } } +}

- return bfqg; +struct bfq_group *bfq_bio_bfqg(struct bfq_data *bfqd, struct bio *bio) +{ + struct blkcg_gq *blkg = bio->bi_blkg; + + if (!blkg) + return bfqd->root_group; + return blkg_to_bfqg(blkg); }

/** @@ -714,25 +705,15 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq, * Move bic to blkcg, assuming that bfqd->lock is held; which makes * sure that the reference to cgroup is valid across the call (see * comments in bfq_bic_update_cgroup on this issue) - * - * NOTE: an alternative approach might have been to store the current - * cgroup in bfqq and getting a reference to it, reducing the lookup - * time here, at the price of slightly more complex code. */ -static struct bfq_group *__bfq_bic_change_cgroup(struct bfq_data *bfqd, - struct bfq_io_cq *bic, - struct blkcg *blkcg) +static void *__bfq_bic_change_cgroup(struct bfq_data *bfqd, + struct bfq_io_cq *bic, + struct bfq_group *bfqg) { struct bfq_queue *async_bfqq = bic_to_bfqq(bic, 0); struct bfq_queue *sync_bfqq = bic_to_bfqq(bic, 1); - struct bfq_group *bfqg; struct bfq_entity *entity;

- bfqg = bfq_find_set_group(bfqd, blkcg); - - if (unlikely(!bfqg)) - bfqg = bfqd->root_group; - if (async_bfqq) { entity = &async_bfqq->entity;

@@ -784,20 +765,24 @@ static struct bfq_group *__bfq_bic_change_cgroup(struct bfq_data *bfqd, void bfq_bic_update_cgroup(struct bfq_io_cq *bic, struct bio *bio) { struct bfq_data *bfqd = bic_to_bfqd(bic); - struct bfq_group *bfqg = NULL; + struct bfq_group *bfqg = bfq_bio_bfqg(bfqd, bio); uint64_t serial_nr;

- rcu_read_lock(); - serial_nr = __bio_blkcg(bio)->css.serial_nr; + serial_nr = bfqg_to_blkg(bfqg)->blkcg->css.serial_nr;

/* * Check whether blkcg has changed. The condition may trigger * spuriously on a newly created cic but there's no harm. */ if (unlikely(!bfqd) || likely(bic->blkcg_serial_nr == serial_nr)) - goto out; + return;

- bfqg = __bfq_bic_change_cgroup(bfqd, bic, __bio_blkcg(bio)); + /* + * New cgroup for this process. Make sure it is linked to bfq internal + * cgroup hierarchy. + */ + bfq_link_bfqg(bfqd, bfqg); + __bfq_bic_change_cgroup(bfqd, bic, bfqg); /* * Update blkg_path for bfq_log_* functions. We cache this * path, and update it here, for the following @@ -850,8 +835,6 @@ void bfq_bic_update_cgroup(struct bfq_io_cq *bic, struct bio *bio) */ blkg_path(bfqg_to_blkg(bfqg), bfqg->blkg_path, sizeof(bfqg->blkg_path)); bic->blkcg_serial_nr = serial_nr; -out: - rcu_read_unlock(); }

/** @@ -1469,7 +1452,7 @@ void bfq_end_wr_async(struct bfq_data *bfqd) bfq_end_wr_async_queues(bfqd, bfqd->root_group); }

-struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd, struct blkcg *blkcg) +struct bfq_group *bfq_bio_bfqg(struct bfq_data *bfqd, struct bio *bio) { return bfqd->root_group; } diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index d7cf930b47bb..e47c75f1fa0f 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -5726,14 +5726,7 @@ static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd, struct bfq_queue *bfqq; struct bfq_group *bfqg;

- rcu_read_lock(); - - bfqg = bfq_find_set_group(bfqd, __bio_blkcg(bio)); - if (!bfqg) { - bfqq = &bfqd->oom_bfqq; - goto out; - } - + bfqg = bfq_bio_bfqg(bfqd, bio); if (!is_sync) { async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class, ioprio); @@ -5779,8 +5772,6 @@ static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,

if (bfqq != &bfqd->oom_bfqq && is_sync && !respawn) bfqq = bfq_do_or_sched_stable_merge(bfqd, bfqq, bic); - - rcu_read_unlock(); return bfqq; }

diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index 4664e2f3e828..978ef5d6fe6a 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -1009,8 +1009,7 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq, void bfq_init_entity(struct bfq_entity *entity, struct bfq_group *bfqg); void bfq_bic_update_cgroup(struct bfq_io_cq *bic, struct bio *bio); void bfq_end_wr_async(struct bfq_data *bfqd); -struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd, - struct blkcg *blkcg); +struct bfq_group *bfq_bio_bfqg(struct bfq_data *bfqd, struct bio *bio); struct blkcg_gq *bfqg_to_blkg(struct bfq_group *bfqg); struct bfq_group *bfqq_group(struct bfq_queue *bfqq); struct bfq_group *bfq_create_group_hierarchy(struct bfq_data *bfqd, int node);