Hi,
在 2023/11/28 7:32, Song Liu 写道:
On Mon, Nov 27, 2023 at 2:16 PM Song Liu <song@xxxxxxxxxx> wrote:
On Fri, Nov 24, 2023 at 10:54 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
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 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 86efc9c2ae56..2ffedc39edd6 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -538,6 +538,9 @@ 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_tryget() from md_flush_request() */
+ percpu_ref_put(&mddev->active_io);
+
/* The pre-request flush has finished */
queue_work(md_wq, &mddev->flush_work);
}
@@ -557,12 +560,8 @@ 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,
@@ -573,7 +572,6 @@ 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))
@@ -626,6 +624,18 @@ 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_tryget()
+ * won't fail, percpu_ref_tryget_live() can't be used because
+ * percpu_ref_kill() can be called by mddev_suspend()
+ * concurrently.
+ */
+ if (WARN_ON(percpu_ref_tryget(&mddev->active_io)))
This should be "if (!WARN_ON(..))", right?
Sorry for the mistake, this actually should be:
if (WARN_ON(!percpu_ref_tryget(...))
Song
+ percpu_ref_get(&mddev->active_io);
Actually, we can just use percpu_ref_get(), no?
Yes, we can, but if someone else doesn't call md_flush_request() under
md_handle_request() in the fulture, there will be problem and
percpu_ref_get() can't catch this, do you think it'll make sense to
prevent such case?
Thanks,
Kuai
Thanks,
Song
.
