[PATCH 5.17 634/772] bfq: Get rid of __bio_blkcg() usage

Greg Kroah-Hartman
2022-06-07T21:38:19Z

From: Jan Kara <jack@suse.cz>

commit 4e54a2493e582361adc3bfbf06c7d50d19d18837 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
block/bfq-cgroup.c | 63 ++++++++++++++++++----------------------------------
block/bfq-iosched.c | 11 ---------
block/bfq-iosched.h | 3 --
3 files changed, 25 insertions(+), 52 deletions(-)

--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -586,27 +586,11 @@ static void bfq_group_set_parent(struct
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(str
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);
}

/**
@@ -706,25 +697,15 @@ void bfq_bfqq_move(struct bfq_data *bfqd
* 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;

@@ -776,20 +757,24 @@ static struct bfq_group *__bfq_bic_chang
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
@@ -842,8 +827,6 @@ void bfq_bic_update_cgroup(struct bfq_io
*/
blkg_path(bfqg_to_blkg(bfqg), bfqg->blkg_path, sizeof(bfqg->blkg_path));
bic->blkcg_serial_nr = serial_nr;
-out:
- rcu_read_unlock();
}

/**
@@ -1461,7 +1444,7 @@ void bfq_end_wr_async(struct bfq_data *b
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;
}
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5730,14 +5730,7 @@ static struct bfq_queue *bfq_get_queue(s
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);
@@ -5783,8 +5776,6 @@ out:

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

--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -1011,8 +1011,7 @@ void bfq_bfqq_move(struct bfq_data *bfqd
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);