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md: synchronize flush io with array reconfiguration

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Currently rcu is used to protect iterating rdev from submit_flushes():

submit_flushes			remove_and_add_spares
				synchronize_rcu
				pers->hot_remove_disk()
 rcu_read_lock()
 rdev_for_each_rcu
  if (rdev->raid_disk >= 0)
				rdev->radi_disk = -1;
   atomic_inc(&rdev->nr_pending)
   rcu_read_unlock()
   bi = bio_alloc_bioset()
   bi->bi_end_io = md_end_flush
   bi->private = rdev
   submit_bio
   // issue io for removed rdev

Fix this problem by grabbing 'acive_io' before iterating rdev, make sure
that remove_and_add_spares() won't concurrent with submit_flushes().

Fixes: a2826aa92e ("md: support barrier requests on all personalities.")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231129020234.1586910-1-yukuai1@huaweicloud.com
This commit is contained in:
Yu Kuai 2023-11-29 10:02:34 +08:00 committed by Song Liu
parent 15da990f8d
commit fa2bbff7b0
1 changed files with 16 additions and 6 deletions
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22
drivers/md/md.c
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@ -529,6 +529,9 @@ static void md_end_flush(struct bio *bio)
rdev_dec_pending(rdev, mddev);
if (atomic_dec_and_test(&mddev->flush_pending)) {
/* The pair is percpu_ref_get() from md_flush_request() */
percpu_ref_put(&mddev->active_io);
/* The pre-request flush has finished */
queue_work(md_wq, &mddev->flush_work);
}
@ -548,12 +551,8 @@ static void submit_flushes(struct work_struct *ws)
rdev_for_each_rcu(rdev, mddev)
if (rdev->raid_disk >= 0 &&
!test_bit(Faulty, &rdev->flags)) {
/* Take two references, one is dropped
* when request finishes, one after
* we reclaim rcu_read_lock
*/
struct bio *bi;
atomic_inc(&rdev->nr_pending);
atomic_inc(&rdev->nr_pending);
rcu_read_unlock();
bi = bio_alloc_bioset(rdev->bdev, 0,
@ -564,7 +563,6 @@ static void submit_flushes(struct work_struct *ws)
atomic_inc(&mddev->flush_pending);
submit_bio(bi);
rcu_read_lock();
rdev_dec_pending(rdev, mddev);
}
rcu_read_unlock();
if (atomic_dec_and_test(&mddev->flush_pending))
@ -617,6 +615,18 @@ bool md_flush_request(struct mddev *mddev, struct bio *bio)
/* new request after previous flush is completed */
if (ktime_after(req_start, mddev->prev_flush_start)) {
WARN_ON(mddev->flush_bio);
/*
* Grab a reference to make sure mddev_suspend() will wait for
* this flush to be done.
*
* md_flush_reqeust() is called under md_handle_request() and
* 'active_io' is already grabbed, hence percpu_ref_is_zero()
* won't pass, percpu_ref_tryget_live() can't be used because
* percpu_ref_kill() can be called by mddev_suspend()
* concurrently.
*/
WARN_ON(percpu_ref_is_zero(&mddev->active_io));
percpu_ref_get(&mddev->active_io);
mddev->flush_bio = bio;
bio = NULL;
}