Revert "md: unlock mddev before reap sync_thread in action_store"

This reverts commit 9dfbdafda3b34e262e43e786077bab8e476a89d1.

Because it will introduce a defect that sync_thread can be running while
MD_RECOVERY_RUNNING is cleared, which will cause some unexpected problems,
for example:

list_add corruption. prev->next should be next (ffff0001ac1daba0), but was ffff0000ce1a02a0. (prev=ffff0000ce1a02a0).
Call trace:
 __list_add_valid+0xfc/0x140
 insert_work+0x78/0x1a0
 __queue_work+0x500/0xcf4
 queue_work_on+0xe8/0x12c
 md_check_recovery+0xa34/0xf30
 raid10d+0xb8/0x900 [raid10]
 md_thread+0x16c/0x2cc
 kthread+0x1a4/0x1ec
 ret_from_fork+0x10/0x18

This is because work is requeued while it's still inside workqueue:

t1:			t2:
action_store
 mddev_lock
  if (mddev->sync_thread)
   mddev_unlock
   md_unregister_thread
   // first sync_thread is done
			md_check_recovery
			 mddev_try_lock
			 /*
			  * once MD_RECOVERY_DONE is set, new sync_thread
			  * can start.
			  */
			 set_bit(MD_RECOVERY_RUNNING, &mddev->recovery)
			 INIT_WORK(&mddev->del_work, md_start_sync)
			 queue_work(md_misc_wq, &mddev->del_work)
			  test_and_set_bit(WORK_STRUCT_PENDING_BIT, ...)
			  // set pending bit
			  insert_work
			   list_add_tail
			 mddev_unlock
   mddev_lock_nointr
   md_reap_sync_thread
   // MD_RECOVERY_RUNNING is cleared
 mddev_unlock

t3:

// before queued work started from t2
md_check_recovery
 // MD_RECOVERY_RUNNING is not set, a new sync_thread can be started
 INIT_WORK(&mddev->del_work, md_start_sync)
  work->data = 0
  // work pending bit is cleared
 queue_work(md_misc_wq, &mddev->del_work)
  insert_work
   list_add_tail
   // list is corrupted

The above commit is reverted to fix the problem, the deadlock this
commit tries to fix will be fixed in following patches.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230529132037.2124527-2-yukuai1@huaweicloud.com

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 8846bf5..1f22bef 100644 (file)
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -3725,7 +3725,6 @@ static int raid_message(struct dm_target *ti, unsigned int argc, char **argv,
        if (!strcasecmp(argv[0], "idle") || !strcasecmp(argv[0], "frozen")) {
                if (mddev->sync_thread) {
                        set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-                       md_unregister_thread(&mddev->sync_thread);
                        md_reap_sync_thread(mddev);
                }
        } else if (decipher_sync_action(mddev, mddev->recovery) != st_idle)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 2e38ef4..d445d5f 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4764,19 +4764,6 @@ action_store(struct mddev *mddev, const char *page, size_t len)
                        if (work_pending(&mddev->del_work))
                                flush_workqueue(md_misc_wq);
                        if (mddev->sync_thread) {
-                               sector_t save_rp = mddev->reshape_position;
-
-                               mddev_unlock(mddev);
-                               set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-                               md_unregister_thread(&mddev->sync_thread);
-                               mddev_lock_nointr(mddev);
-                               /*
-                                * set RECOVERY_INTR again and restore reshape
-                                * position in case others changed them after
-                                * got lock, eg, reshape_position_store and
-                                * md_check_recovery.
-                                */
-                               mddev->reshape_position = save_rp;
                                set_bit(MD_RECOVERY_INTR, &mddev->recovery);
                                md_reap_sync_thread(mddev);
                        }
@@ -6176,7 +6163,6 @@ static void __md_stop_writes(struct mddev *mddev)
                flush_workqueue(md_misc_wq);
        if (mddev->sync_thread) {
                set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-               md_unregister_thread(&mddev->sync_thread);
                md_reap_sync_thread(mddev);
        }
 
@@ -9327,7 +9313,6 @@ void md_check_recovery(struct mddev *mddev)
                         * ->spare_active and clear saved_raid_disk
                         */
                        set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-                       md_unregister_thread(&mddev->sync_thread);
                        md_reap_sync_thread(mddev);
                        clear_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
                        clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
@@ -9363,7 +9348,6 @@ void md_check_recovery(struct mddev *mddev)
                        goto unlock;
                }
                if (mddev->sync_thread) {
-                       md_unregister_thread(&mddev->sync_thread);
                        md_reap_sync_thread(mddev);
                        goto unlock;
                }
@@ -9443,7 +9427,8 @@ void md_reap_sync_thread(struct mddev *mddev)
        sector_t old_dev_sectors = mddev->dev_sectors;
        bool is_reshaped = false;
 
-       /* sync_thread should be unregistered, collect result */
+       /* resync has finished, collect result */
+       md_unregister_thread(&mddev->sync_thread);
        if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery) &&
            !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
            mddev->degraded != mddev->raid_disks) {