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blkcg: update blkg_lookup_create to do locking

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To know when to create a blkg, the general pattern is to do a
blkg_lookup and if that fails, lock and then do a lookup again and if
that fails finally create. It doesn't make much sense for everyone who
wants to do creation to write this themselves.

This changes blkg_lookup_create to do locking and implement this
pattern. The old blkg_lookup_create is renamed to __blkg_lookup_create.
If a call site wants to do its own error handling or already owns the
queue lock, they can use __blkg_lookup_create. This will be used in
upcoming patches.

Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Dennis Zhou (Facebook) 2018-09-11 14:41:27 -04:00 committed by Jens Axboe
parent 27e6fa996c
commit 49f4c2dc2b
3 changed files with 32 additions and 5 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

31
block/blk-cgroup.c
View file

@ -259,7 +259,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
} }
/** /**
* blkg_lookup_create - lookup blkg, try to create one if not there * __blkg_lookup_create - lookup blkg, try to create one if not there
* @blkcg: blkcg of interest * @blkcg: blkcg of interest
* @q: request_queue of interest * @q: request_queue of interest
* *
@ -272,8 +272,8 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
* value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not * value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not
* dead and bypassing, returns ERR_PTR(-EBUSY). * dead and bypassing, returns ERR_PTR(-EBUSY).
*/ */
struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg, struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
struct request_queue *q) struct request_queue *q)
{ {
struct blkcg_gq *blkg; struct blkcg_gq *blkg;
@ -310,6 +310,31 @@ struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
} }
} }
/**
* blkg_lookup_create - find or create a blkg
* @blkcg: target block cgroup
* @q: target request_queue
*
* This looks up or creates the blkg representing the unique pair
* of the blkcg and the request_queue.
*/
struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
struct request_queue *q)
{
struct blkcg_gq *blkg = blkg_lookup(blkcg, q);
unsigned long flags;
if (unlikely(!blkg)) {
spin_lock_irqsave(q->queue_lock, flags);
blkg = __blkg_lookup_create(blkcg, q);
spin_unlock_irqrestore(q->queue_lock, flags);
}
return blkg;
}
static void blkg_destroy(struct blkcg_gq *blkg) static void blkg_destroy(struct blkcg_gq *blkg)
{ {
struct blkcg *blkcg = blkg->blkcg; struct blkcg *blkcg = blkg->blkcg;

2
block/blk-iolatency.c
View file

@ -407,7 +407,7 @@ static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio,
if (unlikely(!blkg)) { if (unlikely(!blkg)) {
if (!lock) if (!lock)
spin_lock_irq(q->queue_lock); spin_lock_irq(q->queue_lock);
blkg = blkg_lookup_create(blkcg, q); blkg = __blkg_lookup_create(blkcg, q);
if (IS_ERR(blkg)) if (IS_ERR(blkg))
blkg = NULL; blkg = NULL;
if (!lock) if (!lock)

4
include/linux/blk-cgroup.h
View file

@ -184,6 +184,8 @@ extern struct cgroup_subsys_state * const blkcg_root_css;
struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg, struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
struct request_queue *q, bool update_hint); struct request_queue *q, bool update_hint);
struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
struct request_queue *q);
struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg, struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
struct request_queue *q); struct request_queue *q);
int blkcg_init_queue(struct request_queue *q); int blkcg_init_queue(struct request_queue *q);
@ -897,7 +899,7 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
blkg = blkg_lookup(blkcg, q); blkg = blkg_lookup(blkcg, q);
if (unlikely(!blkg)) { if (unlikely(!blkg)) {
spin_lock_irq(q->queue_lock); spin_lock_irq(q->queue_lock);
blkg = blkg_lookup_create(blkcg, q); blkg = __blkg_lookup_create(blkcg, q);
if (IS_ERR(blkg)) if (IS_ERR(blkg))
blkg = NULL; blkg = NULL;
spin_unlock_irq(q->queue_lock); spin_unlock_irq(q->queue_lock);