From: Yu Kuai <yukuai1@huaweicloud.com>
To: Guoqing Jiang <guoqing.jiang@linux.dev>,
Yu Kuai <yukuai1@huaweicloud.com>,
logang@deltatee.com, pmenzel@molgen.mpg.de, agk@redhat.com,
snitzer@kernel.org, song@kernel.org
Cc: linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org,
yi.zhang@huawei.com, yangerkun@huawei.com,
Marc Smith <msmith626@gmail.com>,
"yukuai (C)" <yukuai3@huawei.com>
Subject: Re: [PATCH -next 1/6] Revert "md: unlock mddev before reap sync_thread in action_store"
Date: Thu, 23 Mar 2023 14:32:50 +0800 [thread overview]
Message-ID: <3aa073e9-5145-aae2-2201-5ba48c09c693@huaweicloud.com> (raw)
In-Reply-To: <3fc2a539-e4cc-e057-6cf0-da7b3953be6e@linux.dev>
Hi,
在 2023/03/23 11:50, Guoqing Jiang 写道:
> Combined your debug patch with above steps. Seems you are
>
> 1. add delay to action_store, so it can't get lock in time.
> 2. echo "want_replacement"**triggers md_check_recovery which can grab lock
> to start sync thread.
> 3. action_store finally hold lock to clear RECOVERY_RUNNING in reap sync
> thread.
> 4. Then the new added BUG_ON is invoked since RECOVERY_RUNNING is cleared
> in step 3.
Yes, this is exactly what I did.
> sync_thread can be interrupted once MD_RECOVERY_INTR is set which means
> the RUNNING
> can be cleared, so I am not sure the added BUG_ON is reasonable. And
> change BUG_ON
I think BUG_ON() is reasonable because only md_reap_sync_thread can
clear it, md_do_sync will exit quictly if MD_RECOVERY_INTR is set, but
md_do_sync should not see that MD_RECOVERY_RUNNING is cleared, otherwise
there is no gurantee that only one sync_thread can be in progress.
> like this makes more sense to me.
>
> +BUG_ON(!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) &&
> +!test_bit(MD_RECOVERY_INTR, &mddev->recovery));
I think this can be reporduced likewise, md_check_recovery clear
MD_RECOVERY_INTR, and new sync_thread triggered by echo
"want_replacement" won't set this bit.
>
> I think there might be racy window like you described but it should be
> really small, I prefer
> to just add a few lines like this instead of revert and introduce new
> lock to resolve the same
> issue (if it is).
The new lock that I add in this patchset is just try to synchronize idle
and forzen from action_store(patch 3), I can drop it if you think this
is not necessary.
The main changes is patch 4, new lines is not much and I really don't
like to add new flags unless we have to, current code is already hard
to understand...
By the way, I'm concerned that drop the mutex to unregister sync_thread
might not be safe, since the mutex protects lots of stuff, and there
might exist other implicit dependencies.
>
> TBH, I am reluctant to see the changes in the series, it can only be
> considered
> acceptable with conditions:
>
> 1. the previous raid456 bug can be fixed in this way too, hopefully Marc
> or others
> can verify it.
> 2. pass all the tests in mdadm
I already test this patchset with mdadm, If there are reporducer for
raid456 bug, I can try to verify it myself.
Thanks,
Kuai
>
> Thanks,
> Guoqing
> .
>
next prev parent reply other threads:[~2023-03-23 6:32 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-22 6:41 [PATCH -next 0/6] md: fix that MD_RECOVERY_RUNNING can be cleared while sync_thread is still running Yu Kuai
2023-03-22 6:41 ` [PATCH -next 1/6] Revert "md: unlock mddev before reap sync_thread in action_store" Yu Kuai
2023-03-22 7:19 ` Guoqing Jiang
2023-03-22 9:00 ` Yu Kuai
2023-03-22 14:32 ` Guoqing Jiang
2023-03-23 1:36 ` Yu Kuai
2023-03-23 3:50 ` Guoqing Jiang
2023-03-23 6:32 ` Yu Kuai [this message]
2023-03-28 23:58 ` Song Liu
2023-04-06 8:53 ` Yu Kuai
2023-05-05 9:05 ` Yu Kuai
2023-03-22 6:41 ` [PATCH -next 2/6] md: refactor action_store() for 'idle' and 'frozen' Yu Kuai
2023-03-22 6:41 ` [PATCH -next 3/6] md: add a mutex to synchronize idle and frozen in action_store() Yu Kuai
2023-03-22 6:41 ` [PATCH -next 4/6] md: refactor idle/frozen_sync_thread() Yu Kuai
2023-03-22 6:41 ` [PATCH -next 5/6] md: wake up 'resync_wait' at last in md_reap_sync_thread() Yu Kuai
2023-03-22 6:41 ` [PATCH -next 6/6] md: enhance checking in md_check_recovery() Yu Kuai
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