From: Yu Kuai <yukuai3@xxxxxxxxxx>
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@xxxxxxxxxx>
---
Changes in v3:
- use WARN_ON(percpu_ref_is_zero()) and use percpu_ref_get().
Changes in v2:
- Add WARN_ON in case md_flush_request() is not called from
md_handle_request() in future.
drivers/md/md.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 05902e36db66..75ff96d53266 100644
--- 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;
}
--
2.39.2
