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dm-raid: delay flushing event_work() after reconfig_mutex is released

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After commit db5e653d7c ("md: delay choosing sync action to
md_start_sync()"), md_start_sync() will hold 'reconfig_mutex', however,
in order to make sure event_work is done, __md_stop() will flush
workqueue with reconfig_mutex grabbed, hence if sync_work is still
pending, deadlock will be triggered.

Fortunately, former pacthes to fix stopping sync_thread already make sure
all sync_work is done already, hence such deadlock is not possible
anymore. However, in order not to cause confusions for people by this
implicit dependency, delay flushing event_work to dm-raid where
'reconfig_mutex' is not held, and add some comments to emphasize that
the workqueue can't be flushed with 'reconfig_mutex'.

Fixes: db5e653d7c ("md: delay choosing sync action to md_start_sync()")
Depends-on: f52f5c71f3 ("md: fix stopping sync thread")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
This commit is contained in:
Yu Kuai 2023-11-24 15:59:53 +08:00 committed by Mike Snitzer
parent ceb6a6f023
commit db29d79b34
2 changed files with 11 additions and 3 deletions
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3
drivers/md/dm-raid.c
View File

@ -3317,6 +3317,9 @@ static void raid_dtr(struct dm_target *ti)
mddev_lock_nointr(&rs->md);
md_stop(&rs->md);
mddev_unlock(&rs->md);
if (work_pending(&rs->md.event_work))
flush_work(&rs->md.event_work);
raid_set_free(rs);
}

11
drivers/md/md.c
View File

@ -82,6 +82,14 @@ static struct module *md_cluster_mod;
static DECLARE_WAIT_QUEUE_HEAD(resync_wait);
static struct workqueue_struct *md_wq;
/*
* This workqueue is used for sync_work to register new sync_thread, and for
* del_work to remove rdev, and for event_work that is only set by dm-raid.
*
* Noted that sync_work will grab reconfig_mutex, hence never flush this
* workqueue whith reconfig_mutex grabbed.
*/
static struct workqueue_struct *md_misc_wq;
struct workqueue_struct *md_bitmap_wq;
@ -6330,9 +6338,6 @@ static void __md_stop(struct mddev *mddev)
struct md_personality *pers = mddev->pers;
md_bitmap_destroy(mddev);
mddev_detach(mddev);
/* Ensure ->event_work is done */
if (mddev->event_work.func)
flush_workqueue(md_misc_wq);
spin_lock(&mddev->lock);
mddev->pers = NULL;
spin_unlock(&mddev->lock);