On Tue, Nov 28, 2023 at 6:03 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>
Applied to md-next. Thanks!
Song
> ---
> 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
>
>
