[PATCH v2 2/6] md: remove redundant check of 'mddev->sync_thread'

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

The lifetime of sync_thread:

1) Set MD_RECOVERY_NEEDED and wake up daemon thread (by ioctl/sysfs or
   other events);
2) Daemon thread woke up, md_check_recovery() found that
   MD_RECOVERY_NEEDED is set:
   a) try to grab reconfig_mutex;
   b) set MD_RECOVERY_RUNNING;
   c) clear MD_RECOVERY_NEEDED, and then queue sync_work;
3) md_start_sync() choose sync_action, then register sync_thread;
4) md_do_sync() is done, set MD_RECOVERY_DONE and wake up daemon thread;
5) Daemon thread woke up, md_check_recovery() found that
   MD_RECOVERY_DONE is set:
   a) try to grab reconfig_mutex;
   b) unregister sync_thread;
   c) clear MD_RECOVERY_RUNNING and MD_RECOVERY_DONE;

Hence if MD_RECOVERY_RUNNING is not set, mddev->sync_thread must be
NULL, there is no need to judge "mddev->sync_thread == NULL" if
MD_RECOVERY_RUNNING is not set.

Noted that unregister sync_thread(md_reap_sync_thread()) from other
context is wrong and will cause deadlock, for example commit
130443d60b1b ("md: refactor idle/frozen_sync_thread() to fix deadlock").

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 drivers/md/md.c    | 22 +++++++---------------
 drivers/md/raid5.c |  6 ++----
 2 files changed, 9 insertions(+), 19 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 1701e2fb219f..1d33a39d4f13 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3302,8 +3302,7 @@ static ssize_t new_offset_store(struct md_rdev *rdev,
 	if (kstrtoull(buf, 10, &new_offset) < 0)
 		return -EINVAL;
 
-	if (mddev->sync_thread ||
-	    test_bit(MD_RECOVERY_RUNNING,&mddev->recovery))
+	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
 		return -EBUSY;
 	if (new_offset == rdev->data_offset)
 		/* reset is always permitted */
@@ -3987,8 +3986,7 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 	 */
 
 	rv = -EBUSY;
-	if (mddev->sync_thread ||
-	    test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
+	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
 	    mddev->reshape_position != MaxSector ||
 	    mddev->sysfs_active)
 		goto out_unlock;
@@ -4898,8 +4896,7 @@ static void frozen_sync_thread(struct mddev *mddev)
 	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));
+	wait_event(resync_wait, !test_bit(MD_RECOVERY_RUNNING, &mddev->recovery));
 
 	mutex_unlock(&mddev->sync_mutex);
 }
@@ -6388,7 +6385,6 @@ static int md_set_readonly(struct mddev *mddev, struct block_device *bdev)
 
 	mutex_lock(&mddev->open_mutex);
 	if ((mddev->pers && atomic_read(&mddev->openers) > !!bdev) ||
-	    mddev->sync_thread ||
 	    test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
 		pr_warn("md: %s still in use.\n",mdname(mddev));
 		if (did_freeze) {
@@ -6444,15 +6440,13 @@ static int do_md_stop(struct mddev *mddev, int mode,
 	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)));
+	wait_event(resync_wait, !test_bit(MD_RECOVERY_RUNNING,
+					  &mddev->recovery));
 	mddev_lock_nointr(mddev);
 
 	mutex_lock(&mddev->open_mutex);
 	if ((mddev->pers && atomic_read(&mddev->openers) > !!bdev) ||
 	    mddev->sysfs_active ||
-	    mddev->sync_thread ||
 	    test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
 		pr_warn("md: %s still in use.\n",mdname(mddev));
 		mutex_unlock(&mddev->open_mutex);
@@ -7298,8 +7292,7 @@ static int update_size(struct mddev *mddev, sector_t num_sectors)
 	 * of each device.  If num_sectors is zero, we find the largest size
 	 * that fits.
 	 */
-	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
-	    mddev->sync_thread)
+	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
 		return -EBUSY;
 	if (!md_is_rdwr(mddev))
 		return -EROFS;
@@ -7336,8 +7329,7 @@ static int update_raid_disks(struct mddev *mddev, int raid_disks)
 	if (raid_disks <= 0 ||
 	    (mddev->max_disks && raid_disks >= mddev->max_disks))
 		return -EINVAL;
-	if (mddev->sync_thread ||
-	    test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
+	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
 	    test_bit(MD_RESYNCING_REMOTE, &mddev->recovery) ||
 	    mddev->reshape_position != MaxSector)
 		return -EBUSY;
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 4207e945e8c8..ec6cb8185207 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7018,10 +7018,8 @@ raid5_store_stripe_size(struct mddev  *mddev, const char *page, size_t len)
 	pr_debug("md/raid: change stripe_size from %lu to %lu\n",
 			conf->stripe_size, new);
 
-	if (mddev->sync_thread ||
-		test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
-		mddev->reshape_position != MaxSector ||
-		mddev->sysfs_active) {
+	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
+	    mddev->reshape_position != MaxSector || mddev->sysfs_active) {
 		err = -EBUSY;
 		goto out_unlock;
 	}
-- 
2.39.2