On Wed, Feb 03, 2021 at 02:20:22PM +0100, Jack Wang wrote:
> From: Xiao Ni <xni@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Signed-off-by: Xiao Ni <xni@xxxxxxxxxx>
> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> [jwang: backport dc5d17a3c39b06aef866afca19245a9cfb533a79 to 4.19]
I can not take patches backported to older kernels that "skip" kernel
releases.
For example, if I take this into 4.19.y, and then someone moves to 5.4
or 5.10, they will hit the same issue.
So please provide a backported series for all affected releases, back as
far as you want, but never skip releases.
I can't take this series, I'll drop it for now and wait for an updated
set of patches.
thanks,
greg k-h
