Merge branch 'md-suspend-rewrite' into md-next

From Yu Kuai, written by Song Liu

Recent tests with raid10 revealed many issues with the following scenarios:

- add or remove disks to the array
- issue io to the array

At first, we fixed each problem independently respect that io can
concurrent with array reconfiguration. However, with more issues reported
continuously, I am hoping to fix these problems thoroughly.

Refer to how block layer protect io with queue reconfiguration (for
example, change elevator):

blk_mq_freeze_queue
-> wait for all io to be done, and prevent new io to be dispatched
// reconfiguration
blk_mq_unfreeze_queue

I think we can do something similar to synchronize io with array
reconfiguration.

Current synchronization works as the following. For the reconfiguration
operation:

1. Hold 'reconfig_mutex';
2. Check that rdev can be added/removed, one condition is that there is no
   IO (for example, check nr_pending).
3. Do the actual operations to add/remove a rdev, one procedure is
   set/clear a pointer to rdev.
4. Check if there is still no IO on this rdev, if not, revert the
   change.

IO path uses rcu_read_lock/unlock() to access rdev.

- rcu is used wrongly;
- There are lots of places involved that old rdev can be read, however,
many places doesn't handle old value correctly;
- Between step 3 and 4, if new io is dispatched, NULL will be read for
the rdev, and data will be lost if step 4 failed.

The new synchronization is similar to blk_mq_freeze_queue(). To add or
remove disk:

1. Suspend the array, that is, stop new IO from being dispatched
   and wait for inflight IO to finish.
2. Add or remove rdevs to array;
3. Resume the array;

IO path doesn't need to change for now, and all rcu implementation can
be removed.

Then main work is divided into 3 steps:

First, first make sure new apis to suspend the array is general:

- make sure suspend array will wait for io to be done(Done by [1]);
- make sure suspend array can be called for all personalities(Done by [2]);
- make sure suspend array can be called at any time(Done by [3]);
- make sure suspend array doesn't rely on 'reconfig_mutex'(PATCH 3-5);

Second replace old apis with new apis(PATCH 6-16). Specifically, the
synchronization is changed from:

  lock reconfig_mutex
  suspend array
  make changes
  resume array
  unlock reconfig_mutex

to:
   suspend array
   lock reconfig_mutex
   make changes
   unlock reconfig_mutex
   resume array

Finally, for the remain path that involved reconfiguration, suspend the
array first(PATCH 11,12, [4] and PATCH 17):

Preparatory work:
[1] https://lore.kernel.org/all/[email protected]/
[2] https://lore.kernel.org/all/[email protected]/
[3] https://lore.kernel.org/all/[email protected]/
[4] https://lore.kernel.org/all/[email protected]/

* md-suspend-rewrite:
  md: rename __mddev_suspend/resume() back to mddev_suspend/resume()
  md: remove old apis to suspend the array
  md: suspend array in md_start_sync() if array need reconfiguration
  md/raid5: replace suspend with quiesce() callback
  md/md-linear: cleanup linear_add()
  md: cleanup mddev_create/destroy_serial_pool()
  md: use new apis to suspend array before mddev_create/destroy_serial_pool
  md: use new apis to suspend array for ioctls involed array reconfiguration
  md: use new apis to suspend array for adding/removing rdev from state_store()
  md: use new apis to suspend array for sysfs apis
  md/raid5: use new apis to suspend array
  md/raid5-cache: use new apis to suspend array
  md/md-bitmap: use new apis to suspend array for location_store()
  md/dm-raid: use new apis to suspend array
  md: add new helpers to suspend/resume and lock/unlock array
  md: add new helpers to suspend/resume array
  md: replace is_md_suspended() with 'mddev->suspended' in md_check_recovery()
  md/raid5-cache: use READ_ONCE/WRITE_ONCE for 'conf->log'
  md: use READ_ONCE/WRITE_ONCE for 'suspend_lo' and 'suspend_hi'

drivers/md/dm-raid.c

@@ -3244,7 +3244,7 @@ static int raid_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	set_bit(MD_RECOVERY_FROZEN, &rs->md.recovery);
 
 	/* Has to be held on running the array */
-	mddev_lock_nointr(&rs->md);
+	mddev_suspend_and_lock_nointr(&rs->md);
 	r = md_run(&rs->md);
 	rs->md.in_sync = 0; /* Assume already marked dirty */
 	if (r) {
@@ -3268,7 +3268,6 @@ static int raid_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		}
 	}
 
-	mddev_suspend(&rs->md);
 	set_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags);
 
 	/* Try to adjust the raid4/5/6 stripe cache size to the stripe size */
@@ -3798,9 +3797,7 @@ static void raid_postsuspend(struct dm_target *ti)
 		if (!test_bit(MD_RECOVERY_FROZEN, &rs->md.recovery))
 			md_stop_writes(&rs->md);
 
-		mddev_lock_nointr(&rs->md);
-		mddev_suspend(&rs->md);
-		mddev_unlock(&rs->md);
+		mddev_suspend(&rs->md, false);
 	}
 }
 
@@ -4059,8 +4056,7 @@ static void raid_resume(struct dm_target *ti)
 		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 		mddev->ro = 0;
 		mddev->in_sync = 0;
-		mddev_resume(mddev);
-		mddev_unlock(mddev);
+		mddev_unlock_and_resume(mddev);
 	}
 }
 

drivers/md/md-autodetect.c

@@ -175,7 +175,7 @@ static void __init md_setup_drive(struct md_setup_args *args)
 		return;
 	}
 
-	err = mddev_lock(mddev);
+	err = mddev_suspend_and_lock(mddev);
 	if (err) {
 		pr_err("md: failed to lock array %s\n", name);
 		goto out_mddev_put;
@@ -221,7 +221,7 @@ static void __init md_setup_drive(struct md_setup_args *args)
 	if (err)
 		pr_warn("md: starting %s failed\n", name);
 out_unlock:
-	mddev_unlock(mddev);
+	mddev_unlock_and_resume(mddev);
 out_mddev_put:
 	mddev_put(mddev);
 }

drivers/md/md-bitmap.c

@@ -1861,7 +1861,7 @@ void md_bitmap_destroy(struct mddev *mddev)
 
 	md_bitmap_wait_behind_writes(mddev);
 	if (!mddev->serialize_policy)
-		mddev_destroy_serial_pool(mddev, NULL, true);
+		mddev_destroy_serial_pool(mddev, NULL);
 
 	mutex_lock(&mddev->bitmap_info.mutex);
 	spin_lock(&mddev->lock);
@@ -1977,7 +1977,7 @@ int md_bitmap_load(struct mddev *mddev)
 		goto out;
 
 	rdev_for_each(rdev, mddev)
-		mddev_create_serial_pool(mddev, rdev, true);
+		mddev_create_serial_pool(mddev, rdev);
 
 	if (mddev_is_clustered(mddev))
 		md_cluster_ops->load_bitmaps(mddev, mddev->bitmap_info.nodes);
@@ -2348,11 +2348,10 @@ location_store(struct mddev *mddev, const char *buf, size_t len)
 {
 	int rv;
 
-	rv = mddev_lock(mddev);
+	rv = mddev_suspend_and_lock(mddev);
 	if (rv)
 		return rv;
 
-	mddev_suspend(mddev);
 	if (mddev->pers) {
 		if (mddev->recovery || mddev->sync_thread) {
 			rv = -EBUSY;
@@ -2429,8 +2428,7 @@ location_store(struct mddev *mddev, const char *buf, size_t len)
 	}
 	rv = 0;
 out:
-	mddev_resume(mddev);
-	mddev_unlock(mddev);
+	mddev_unlock_and_resume(mddev);
 	if (rv)
 		return rv;
 	return len;
@@ -2539,7 +2537,7 @@ backlog_store(struct mddev *mddev, const char *buf, size_t len)
 	if (backlog > COUNTER_MAX)
 		return -EINVAL;
 
-	rv = mddev_lock(mddev);
+	rv = mddev_suspend_and_lock(mddev);
 	if (rv)
 		return rv;
 
@@ -2564,16 +2562,16 @@ backlog_store(struct mddev *mddev, const char *buf, size_t len)
 	if (!backlog && mddev->serial_info_pool) {
 		/* serial_info_pool is not needed if backlog is zero */
 		if (!mddev->serialize_policy)
-			mddev_destroy_serial_pool(mddev, NULL, false);
+			mddev_destroy_serial_pool(mddev, NULL);
 	} else if (backlog && !mddev->serial_info_pool) {
 		/* serial_info_pool is needed since backlog is not zero */
 		rdev_for_each(rdev, mddev)
-			mddev_create_serial_pool(mddev, rdev, false);
+			mddev_create_serial_pool(mddev, rdev);
 	}
 	if (old_mwb != backlog)
 		md_bitmap_update_sb(mddev->bitmap);
 
-	mddev_unlock(mddev);
+	mddev_unlock_and_resume(mddev);
 	return len;
 }
 

drivers/md/md-linear.c

@@ -183,7 +183,6 @@ static int linear_add(struct mddev *mddev, struct md_rdev *rdev)
 	 * in linear_congested(), therefore kfree_rcu() is used to free
 	 * oldconf until no one uses it anymore.
 	 */
-	mddev_suspend(mddev);
 	oldconf = rcu_dereference_protected(mddev->private,
 			lockdep_is_held(&mddev->reconfig_mutex));
 	mddev->raid_disks++;
@@ -192,7 +191,6 @@ static int linear_add(struct mddev *mddev, struct md_rdev *rdev)
 	rcu_assign_pointer(mddev->private, newconf);
 	md_set_array_sectors(mddev, linear_size(mddev, 0, 0));
 	set_capacity_and_notify(mddev->gendisk, mddev->array_sectors);
-	mddev_resume(mddev);
 	kfree_rcu(oldconf, rcu);
 	return 0;
 }