linux-kernel - Re: [PATCH -next 1/8] md/raid10: prevent soft lockup while flush writes

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Date:   Mon, 24 Apr 2023 23:39:35 -0700
From:   Song Liu <song@...nel.org>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     neilb@...e.de, akpm@...l.org, linux-raid@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next 1/8] md/raid10: prevent soft lockup while flush writes

On Mon, Apr 24, 2023 at 11:16 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> Hi,
>
> 在 2023/04/25 8:23, Song Liu 写道:
> > On Thu, Apr 20, 2023 at 4:31 AM Yu Kuai <yukuai1@...weicloud.com> wrote:
> >>
> >> From: Yu Kuai <yukuai3@...wei.com>
> >>
> >> Currently, there is no limit for raid1/raid10 plugged bio. While flushing
> >> writes, raid1 has cond_resched() while raid10 doesn't, and too many
> >> writes can cause soft lockup.
> >>
> >> Follow up soft lockup can be triggered easily with writeback test for
> >> raid10 with ramdisks:
> >>
> >> watchdog: BUG: soft lockup - CPU#10 stuck for 27s! [md0_raid10:1293]
> >> Call Trace:
> >>   <TASK>
> >>   call_rcu+0x16/0x20
> >>   put_object+0x41/0x80
> >>   __delete_object+0x50/0x90
> >>   delete_object_full+0x2b/0x40
> >>   kmemleak_free+0x46/0xa0
> >>   slab_free_freelist_hook.constprop.0+0xed/0x1a0
> >>   kmem_cache_free+0xfd/0x300
> >>   mempool_free_slab+0x1f/0x30
> >>   mempool_free+0x3a/0x100
> >>   bio_free+0x59/0x80
> >>   bio_put+0xcf/0x2c0
> >>   free_r10bio+0xbf/0xf0
> >>   raid_end_bio_io+0x78/0xb0
> >>   one_write_done+0x8a/0xa0
> >>   raid10_end_write_request+0x1b4/0x430
> >>   bio_endio+0x175/0x320
> >>   brd_submit_bio+0x3b9/0x9b7 [brd]
> >>   __submit_bio+0x69/0xe0
> >>   submit_bio_noacct_nocheck+0x1e6/0x5a0
> >>   submit_bio_noacct+0x38c/0x7e0
> >>   flush_pending_writes+0xf0/0x240
> >>   raid10d+0xac/0x1ed0
> >
> > Is it possible to trigger this with a mdadm test?
> >
>
> The test I mentioned in patch 8 can trigger this problem reliablity, so
> I this add a new test can achieve this.

To be clear, by "mdadm test" I mean the tests included in mdadm:

https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/tree/tests

Could you please try to add a test? If it works, we should add it to
mdadm.

Thanks,
Song