Re: [PATCH -next 1/3] md/raid10: fix improper BUG_ON() in raise_barrier()

From: "John Stoffel" <john@stoffel.org>
To: Yu Kuai <yukuai1@huaweicloud.com>
Cc: song@kernel.org, linux-raid@vger.kernel.org,
	linux-kernel@vger.kernel.org, yukuai3@huawei.com,
	yi.zhang@huawei.com
Subject: Re: [PATCH -next 1/3] md/raid10: fix improper BUG_ON() in raise_barrier()
Date: Mon, 29 Aug 2022 15:53:57 -0400	[thread overview]
Message-ID: <25357.6485.659159.476926@quad.stoffel.home> (raw)
In-Reply-To: <20220829131502.165356-2-yukuai1@huaweicloud.com>

>>>>> "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?

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