linux-kernel - [PATCH AUTOSEL 5.15 19/23] md: Flush workqueue md_rdev_misc_wq in md

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Date:   Tue, 30 Aug 2022 13:21:36 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     David Sloan <david.sloan@...eticom.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Song Liu <song@...nel.org>, Sasha Levin <sashal@...nel.org>,
        linux-raid@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 19/23] md: Flush workqueue md_rdev_misc_wq in md_alloc()

From: David Sloan <david.sloan@...eticom.com>

[ Upstream commit 5e8daf906f890560df430d30617c692a794acb73 ]

A race condition still exists when removing and re-creating md devices
in test cases. However, it is only seen on some setups.

The race condition was tracked down to a reference still being held
to the kobject by the rdev in the md_rdev_misc_wq which will be released
in rdev_delayed_delete().

md_alloc() waits for previous deletions by waiting on the md_misc_wq,
but the md_rdev_misc_wq may still be holding a reference to a recently
removed device.

To fix this, also flush the md_rdev_misc_wq in md_alloc().

Signed-off-by: David Sloan <david.sloan@...eticom.com>
[logang@...tatee.com: rewrote commit message]
Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
Signed-off-by: Song Liu <song@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/md/md.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 33946adb0d6f6..17100b39ff14a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5651,6 +5651,7 @@ static int md_alloc(dev_t dev, char *name)
 	 * removed (mddev_delayed_delete).
 	 */
 	flush_workqueue(md_misc_wq);
+	flush_workqueue(md_rdev_misc_wq);
 
 	mutex_lock(&disks_mutex);
 	mddev = mddev_alloc(dev);
-- 
2.35.1