From: Xiao Ni xni@redhat.com

One customer reports a crash problem which causes by flush request. It triggers a warning before crash.

/* new request after previous flush is completed */ if (ktime_after(req_start, mddev->prev_flush_start)) { WARN_ON(mddev->flush_bio); mddev->flush_bio = bio; bio = NULL; }

The WARN_ON is triggered. We use spin lock to protect prev_flush_start and flush_bio in md_flush_request. But there is no lock protection in md_submit_flush_data. It can set flush_bio to NULL first because of compiler reordering write instructions.

For example, flush bio1 sets flush bio to NULL first in md_submit_flush_data. An interrupt or vmware causing an extended stall happen between updating flush_bio and prev_flush_start. Because flush_bio is NULL, flush bio2 can get the lock and submit to underlayer disks. Then flush bio1 updates prev_flush_start after the interrupt or extended stall.

Then flush bio3 enters in md_flush_request. The start time req_start is behind prev_flush_start. The flush_bio is not NULL(flush bio2 hasn't finished). So it can trigger the WARN_ON now. Then it calls INIT_WORK again. INIT_WORK() will re-initialize the list pointers in the work_struct, which then can result in a corrupted work list and the work_struct queued a second time. With the work list corrupted, it can lead in invalid work items being used and cause a crash in process_one_work.

We need to make sure only one flush bio can be handled at one same time. So add spin lock in md_submit_flush_data to protect prev_flush_start and flush_bio in an atomic way.

Reviewed-by: David Jeffery djeffery@redhat.com Signed-off-by: Xiao Ni xni@redhat.com Signed-off-by: Song Liu songliubraving@fb.com [jwang: backport dc5d17a3c39b06aef866afca19245a9cfb533a79] Signed-off-by: Jack Wang jinpu.wang@cloud.ionos.com --- drivers/md/md.c | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c index ec5dfb7ae4e1..cc38530804c9 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -538,8 +538,10 @@ static void md_submit_flush_data(struct work_struct *ws) * could wait for this and below md_handle_request could wait for those * bios because of suspend check */ + spin_lock_irq(&mddev->lock); mddev->last_flush = mddev->start_flush; mddev->flush_bio = NULL; + spin_unlock_irq(&mddev->lock); wake_up(&mddev->sb_wait);

if (bio->bi_iter.bi_size == 0) {