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Subject: Re: [PATCH -next 1/8] md/raid10: prevent soft lockup while flush
 writes
To:     Song Liu <song@kernel.org>, Yu Kuai <yukuai1@huaweicloud.com>
Cc:     neilb@suse.de, akpm@osdl.org, linux-raid@vger.kernel.org,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
        yangerkun@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
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From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <994e902f-b912-3bab-ac8d-e8c1dd2e17d3@huaweicloud.com>
Date:   Tue, 25 Apr 2023 14:47:22 +0800
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Hi,

在 2023/04/25 14:39, Song Liu 写道:
> On Mon, Apr 24, 2023 at 11:16 PM Yu Kuai <yukuai1@huaweicloud.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@huaweicloud.com> wrote:
>>>>
>>>> From: Yu Kuai <yukuai3@huawei.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.

Yes, of course. However, I'm not familiar how mdadm tests works yet, it
might take some time. By the way, I'll be good if I can add the test to
blktests if possible.

Thanks,
Kuai
> 
> Thanks,
> Song
> .
>