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Subject: Re: [PATCH -next 1/3] md/raid10: fix improper BUG_ON() in
 raise_barrier()
To:     John Stoffel <john@stoffel.org>, Yu Kuai <yukuai1@huaweicloud.com>
Cc:     song@kernel.org, linux-raid@vger.kernel.org,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20220829131502.165356-1-yukuai1@huaweicloud.com>
 <20220829131502.165356-2-yukuai1@huaweicloud.com>
 <25357.6485.659159.476926@quad.stoffel.home>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <d46162b3-cd7c-cbc5-0ded-bb62a8a03ca5@huaweicloud.com>
Date:   Tue, 30 Aug 2022 09:01:49 +0800
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Hi, John

?? 2022/08/30 3:53, John Stoffel д??:
>>>>>> "Yu" == Yu Kuai <yukuai1@huaweicloud.com> writes:
> 
> Yu> From: Yu Kuai <yukuai3@huawei.com>
> Yu> 'conf->barrier' is protected by 'conf->resync_lock', reading
> Yu> 'conf->barrier' without holding the lock is wrong.
> 
> Yu> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> Yu> ---
> Yu>  drivers/md/raid10.c | 2 +-
> Yu>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Yu> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> Yu> index 9117fcdee1be..b70c207f7932 100644
> Yu> --- a/drivers/md/raid10.c
> Yu> +++ b/drivers/md/raid10.c
> Yu> @@ -930,8 +930,8 @@ static void flush_pending_writes(struct r10conf *conf)
>   
> Yu>  static void raise_barrier(struct r10conf *conf, int force)
> Yu>  {
> Yu> -	BUG_ON(force && !conf->barrier);
> Yu>  	spin_lock_irq(&conf->resync_lock);
> Yu> +	BUG_ON(force && !conf->barrier);
> 
> I don't like this BUG_ON() at all, why are you crashing the system
> here instead of just doing a simple WARN_ONCE() instead?  Is there
> anything the user can do to get into this situation on their own, or
> does it really signify a logic error in the code?  If so, why are you
> killing the system?

I'm not sure why to use the BUG_ON() here. I just noticed that
'conf->barrier' is read without holding 'resync_lock', and BUG_ON() can
be triggered false positive.

Thanks,
Kuai
> 
> 
>   
> Yu>  	/* Wait until no block IO is waiting (unless 'force') */
> Yu>  	wait_event_lock_irq(conf->wait_barrier, force || !conf->nr_waiting,
> Yu> --
> Yu> 2.31.1
> 
> 
> .
>