linux-kernel - Re: [PATCH 5.10 050/530] md: md_open returns -EBUSY when entering racing area

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Date:   Thu, 13 May 2021 09:59:41 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 5.10 050/530] md: md_open returns -EBUSY when entering
 racing area

Hi!

> commit 6a4db2a60306eb65bfb14ccc9fde035b74a4b4e7 upstream.
> 
> commit d3374825ce57 ("md: make devices disappear when they are no longer
> needed.") introduced protection between mddev creating & removing. The
> md_open shouldn't create mddev when all_mddevs list doesn't contain
> mddev. With currently code logic, there will be very easy to trigger
> soft lockup in non-preempt env.
> 
> This patch changes md_open returning from -ERESTARTSYS to -EBUSY, which
> will break the infinitely retry when md_open enter racing area.
> 
> This patch is partly fix soft lockup issue, full fix needs mddev_find
> is split into two functions: mddev_find & mddev_find_or_alloc. And
> md_open should call new mddev_find (it only does searching job).
> 
> For more detail, please refer with Christoph's "split mddev_find" patch
> in later commits.

Something went wrong here; changelog is truncated, in particular it
does not contain required sign-offs.

Best regards,
								Pavel

> +++ b/drivers/md/md.c
> @@ -7857,8 +7857,7 @@ static int md_open(struct block_device *
>  		/* Wait until bdev->bd_disk is definitely gone */
>  		if (work_pending(&mddev->del_work))
>  			flush_workqueue(md_misc_wq);
> -		/* Then retry the open from the top */
> -		return -ERESTARTSYS;
> +		return -EBUSY;
>  	}
>  	BUG_ON(mddev != bdev->bd_disk->private_data);


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