md: synchronize flush io with array reconfiguration

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: a2826aa92e2e ("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

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 71b3397dea475f86cc7e9ea8a419085e9006f2df..4e9fe5cbeedc879035b37ed42ab57d2dfd7e657f 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -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;
        }