[PATCH -next 2/2] md/md-bitmap: hold 'reconfig_mutex' in backlog_store()

[Yu Kuai]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

Several reasons why 'reconfig_mutex' should be held:

1) rdev_for_each() is not safe to be called without the lock, because
   rdev can be removed concurrently.
2) mddev_destroy_serial_pool() and mddev_create_serial_pool() should not
   be called concurrently.
3) mddev_suspend() from mddev_destroy/create_serial_pool() should be
   protected by the lock.

Fixes: 10c92fca636e ("md-bitmap: create and destroy wb_info_pool with the change of backlog")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 drivers/md/md-bitmap.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 1f3339961159..6f9ff14971f9 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -2546,6 +2546,10 @@ backlog_store(struct mddev *mddev, const char *buf, size_t len)
 	if (backlog > COUNTER_MAX)
 		return -EINVAL;
 
+	rv = mddev_lock(mddev);
+	if (rv)
+		return rv;
+
 	/*
 	 * Without write mostly device, it doesn't make sense to set
 	 * backlog for max_write_behind.
@@ -2559,6 +2563,7 @@ backlog_store(struct mddev *mddev, const char *buf, size_t len)
 	if (!has_write_mostly) {
 		pr_warn_ratelimited("%s: can't set backlog, no write mostly device available\n",
 				    mdname(mddev));
+		mddev_unlock(mddev);
 		return -EINVAL;
 	}
 
@@ -2574,6 +2579,8 @@ backlog_store(struct mddev *mddev, const char *buf, size_t len)
 	}
 	if (old_mwb != backlog)
 		md_bitmap_update_sb(mddev->bitmap);
+
+	mddev_unlock(mddev);
 	return len;
 }
 
-- 
2.39.2