Commit f52f5c71 authored by Yu Kuai's avatar Yu Kuai Committed by Song Liu
Browse files

md: fix stopping sync thread 



Currently sync thread is stopped from multiple contex:
 - idle_sync_thread
 - frozen_sync_thread
 - __md_stop_writes
 - md_set_readonly
 - do_md_stop

And there are some problems:
1) sync_work is flushed while reconfig_mutex is grabbed, this can
   deadlock because the work function will grab reconfig_mutex as well.
2) md_reap_sync_thread() can't be called directly while md_do_sync() is
   not finished yet, for example, commit 130443d6 ("md: refactor
   idle/frozen_sync_thread() to fix deadlock").
3) If MD_RECOVERY_RUNNING is not set, there is no need to stop
   sync_thread at all because sync_thread must not be registered.

Factor out a helper stop_sync_thread(), so that above contex will behave
the same. Fix 1) by flushing sync_work after reconfig_mutex is released,
before waiting for sync_thread to be done; Fix 2) bt letting daemon thread
to unregister sync_thread; Fix 3) by always checking MD_RECOVERY_RUNNING
first.

Fixes: db5e653d ("md: delay choosing sync action to md_start_sync()")
Signed-off-by: default avatarYu Kuai <yukuai3@huawei.com>
Signed-off-by: default avatarSong Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231205094215.1824240-4-yukuai1@huaweicloud.com
parent c9f7cb5b

drivers/md/md.c

+37 −53
Original line number Diff line number Diff line
@@ -4840,25 +4840,29 @@ action_show(struct mddev *mddev, char *page) 
	return sprintf(page, "%s\n", type);

}



static void stop_sync_thread(struct mddev *mddev)

/**

 * stop_sync_thread() - wait for sync_thread to stop if it's running.

 * @mddev:	the array.

 * @locked:	if set, reconfig_mutex will still be held after this function

 *		return; if not set, reconfig_mutex will be released after this

 *		function return.

 * @check_seq:	if set, only wait for curent running sync_thread to stop, noted

 *		that new sync_thread can still start.

 */

static void stop_sync_thread(struct mddev *mddev, bool locked, bool check_seq)

{

	if (!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))

		return;

	int sync_seq;



	if (mddev_lock(mddev))

		return;

	if (check_seq)

		sync_seq = atomic_read(&mddev->sync_seq);



	/*

	 * Check again in case MD_RECOVERY_RUNNING is cleared before lock is

	 * held.

	 */

	if (!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {

		if (!locked)

			mddev_unlock(mddev);

		return;

	}



	if (work_pending(&mddev->sync_work))

		flush_workqueue(md_misc_wq);

	mddev_unlock(mddev);



	set_bit(MD_RECOVERY_INTR, &mddev->recovery);

	/*
@@ -4866,21 +4870,28 @@ static void stop_sync_thread(struct mddev *mddev) 
	 * never happen

	 */

	md_wakeup_thread_directly(mddev->sync_thread);

	if (work_pending(&mddev->sync_work))

		flush_work(&mddev->sync_work);



	mddev_unlock(mddev);

	wait_event(resync_wait,

		   !test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||

		   (check_seq && sync_seq != atomic_read(&mddev->sync_seq)));



	if (locked)

		mddev_lock_nointr(mddev);

}



static void idle_sync_thread(struct mddev *mddev)

{

	int sync_seq = atomic_read(&mddev->sync_seq);



	mutex_lock(&mddev->sync_mutex);

	clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);

	stop_sync_thread(mddev);



	wait_event(resync_wait, sync_seq != atomic_read(&mddev->sync_seq) ||

			!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery));

	if (mddev_lock(mddev)) {

		mutex_unlock(&mddev->sync_mutex);

		return;

	}



	stop_sync_thread(mddev, false, true);

	mutex_unlock(&mddev->sync_mutex);

}
@@ -4888,11 +4899,13 @@ static void frozen_sync_thread(struct mddev *mddev) 
{

	mutex_lock(&mddev->sync_mutex);

	set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);

	stop_sync_thread(mddev);



	wait_event(resync_wait, mddev->sync_thread == NULL &&

			!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery));

	if (mddev_lock(mddev)) {

		mutex_unlock(&mddev->sync_mutex);

		return;

	}



	stop_sync_thread(mddev, false, false);

	mutex_unlock(&mddev->sync_mutex);

}
@@ -6264,14 +6277,7 @@ static void md_clean(struct mddev *mddev) 


static void __md_stop_writes(struct mddev *mddev)

{

	set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);

	if (work_pending(&mddev->sync_work))

		flush_workqueue(md_misc_wq);

	if (mddev->sync_thread) {

		set_bit(MD_RECOVERY_INTR, &mddev->recovery);

		md_reap_sync_thread(mddev);

	}



	stop_sync_thread(mddev, true, false);

	del_timer_sync(&mddev->safemode_timer);



	if (mddev->pers && mddev->pers->quiesce) {
@@ -6363,18 +6369,8 @@ static int md_set_readonly(struct mddev *mddev, struct block_device *bdev) 
		set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);

		md_wakeup_thread(mddev->thread);

	}

	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))

		set_bit(MD_RECOVERY_INTR, &mddev->recovery);



	/*

	 * Thread might be blocked waiting for metadata update which will now

	 * never happen

	 */

	md_wakeup_thread_directly(mddev->sync_thread);



	mddev_unlock(mddev);

	wait_event(resync_wait, !test_bit(MD_RECOVERY_RUNNING,

					  &mddev->recovery));

	stop_sync_thread(mddev, false, false);

	wait_event(mddev->sb_wait,

		   !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags));

	mddev_lock_nointr(mddev);
@@ -6428,20 +6424,8 @@ static int do_md_stop(struct mddev *mddev, int mode, 
		set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);

		md_wakeup_thread(mddev->thread);

	}

	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))

		set_bit(MD_RECOVERY_INTR, &mddev->recovery);



	/*

	 * Thread might be blocked waiting for metadata update which will now

	 * never happen

	 */

	md_wakeup_thread_directly(mddev->sync_thread);



	mddev_unlock(mddev);

	wait_event(resync_wait, (mddev->sync_thread == NULL &&

				 !test_bit(MD_RECOVERY_RUNNING,

					   &mddev->recovery)));

	mddev_lock_nointr(mddev);

	stop_sync_thread(mddev, true, false);



	mutex_lock(&mddev->open_mutex);

	if ((mddev->pers && atomic_read(&mddev->openers) > !!bdev) ||