Re: [PATCH 1/3] raid5: call clear_batch_ready before set STRIPE_ACTIVE

[Song Liu <song@kernel.org>]

On Thu, Jul 16, 2020 at 12:45 AM Guoqing Jiang
<guoqing.jiang@cloud.ionos.com> wrote:
>
> On 6/26/20 2:16 AM, Song Liu wrote:
> > On Thu, Jun 25, 2020 at 2:22 AM Guoqing Jiang
> > <guoqing.jiang@cloud.ionos.com> wrote:
> >>
> >>
> >> On 6/24/20 1:58 AM, Song Liu wrote:
> >>> On Tue, Jun 16, 2020 at 2:25 AM Guoqing Jiang
> >>> <guoqing.jiang@cloud.ionos.com> wrote:
> >>>> We tried to only put the head sh of batch list to handle_list, then the
> >>>> handle_stripe doesn't handle other members in the batch list. However,
> >>>> we still got the calltrace in break_stripe_batch_list.
> >>>>
> >>>> [593764.644269] stripe state: 2003
> >>>> kernel: [593764.644299] ------------[ cut here ]------------
> >>>> kernel: [593764.644308] WARNING: CPU: 12 PID: 856 at drivers/md/raid5.c:4625 break_stripe_batch_list+0x203/0x240 [raid456]
> >>>> [...]
> >>>> kernel: [593764.644363] Call Trace:
> >>>> kernel: [593764.644370]  handle_stripe+0x907/0x20c0 [raid456]
> >>>> kernel: [593764.644376]  ? __wake_up_common_lock+0x89/0xc0
> >>>> kernel: [593764.644379]  handle_active_stripes.isra.57+0x35f/0x570 [raid456]
> >>>> kernel: [593764.644382]  ? raid5_wakeup_stripe_thread+0x96/0x1f0 [raid456]
> >>>> kernel: [593764.644385]  raid5d+0x480/0x6a0 [raid456]
> >>>> kernel: [593764.644390]  ? md_thread+0x11f/0x160
> >>>> kernel: [593764.644392]  md_thread+0x11f/0x160
> >>>> kernel: [593764.644394]  ? wait_woken+0x80/0x80
> >>>> kernel: [593764.644396]  kthread+0xfc/0x130
> >>>> kernel: [593764.644398]  ? find_pers+0x70/0x70
> >>>> kernel: [593764.644399]  ? kthread_create_on_node+0x70/0x70
> >>>> kernel: [593764.644401]  ret_from_fork+0x1f/0x30
> >>>>
> >>>> As we can see, the stripe was set with STRIPE_ACTIVE and STRIPE_HANDLE,
> >>>> and only handle_stripe could set those flags then return. And since the
> >>>> stipe was already in the batch list, we need to return earlier before
> >>>> set the two flags.
> >>>>
> >>>> And after dig a little about git history especially commit 3664847d95e6
> >>>> ("md/raid5: fix a race condition in stripe batch"), it seems the batched
> >>>> stipe still could be handled by handle_stipe, then handle_stipe needs to
> >>>> return earlier if clear_batch_ready to return true.
> >>>>
> >>>> Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
> >>>> ---
> >>>> Another alternative would be just not warn if STRIPE_ACTIVE is valid for
> >>>> the batched list.
> >>>>
> >>>> What do you think?
> >>>>
> >>> This patch looks good to me (haven't tested yet). Let's try with this one.
> >> Ok, pls let me know if there is issue during test.
> >>
> >> And do you want a new patch to reflect which I clarified for the line
> >> number and kernel version?
> > That's not necessary. If needed, I will make some change when I apply the patch.
>
> May I know your decision about this?
>

I am sorry that I missed this one. Applied to md-next.

Thanks,
Song

> Thanks,
> Guoqing