Re: [stable-4.19 8/8] md: Set prev_flush_start and flush_bio in an atomic way

From: Greg KH <gregkh@linuxfoundation.org>
To: Jack Wang <jinpu.wang@cloud.ionos.com>
Cc: sashal@kernel.org, stable@vger.kernel.org,
	Xiao Ni <xni@redhat.com>, David Jeffery <djeffery@redhat.com>,
	Song Liu <songliubraving@fb.com>
Subject: Re: [stable-4.19 8/8] md: Set prev_flush_start and flush_bio in an atomic way
Date: Thu, 4 Feb 2021 16:12:44 +0100	[thread overview]
Message-ID: <YBwO7EsBfljWNliY@kroah.com> (raw)
In-Reply-To: <20210203132022.92406-9-jinpu.wang@cloud.ionos.com>

On Wed, Feb 03, 2021 at 02:20:22PM +0100, Jack Wang wrote:
> 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 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