[PATCH 5.11 052/601] md: md_open returns -EBUSY when entering racing area

Greg Kroah-Hartman
2021-05-12T16:53:25Z

From: Zhao Heming <heming.zhao@suse.com>

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.

---
drivers/md/md.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7856,8 +7856,7 @@ 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);