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md: md_open returns -EBUSY when entering racing area

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commit 6a4db2a60306eb65bfb14ccc9fde035b74a4b4e7 upstream.

commit d3374825ce ("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.
This commit is contained in:
Zhao Heming 2021-04-03 11:01:25 +08:00 • committed by Greg Kroah-Hartman
commit 79c1bfae66
1 changed files with 1 additions and 2 deletions
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3
drivers/md/md.c
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@ -7638,8 +7638,7 @@ static int md_open(struct block_device *bdev, fmode_t mode)
/* 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);