Merge remote-tracking branch 'torvalds/master' into perf/core

To pick fixes that went via perf/urgent.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 17 insertions, 8 deletions

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 00851c86aa8a..af97413abcf4 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -3367,6 +3367,7 @@ static void btrfs_qgroup_rescan_worker(struct btrfs_work *work)
 	int err = -ENOMEM;
 	int ret = 0;
 	bool stopped = false;
+	bool did_leaf_rescans = false;
 
 	path = btrfs_alloc_path();
 	if (!path)
@@ -3387,6 +3388,7 @@ static void btrfs_qgroup_rescan_worker(struct btrfs_work *work)
 		}
 
 		err = qgroup_rescan_leaf(trans, path);
+		did_leaf_rescans = true;
 
 		if (err > 0)
 			btrfs_commit_transaction(trans);
@@ -3407,16 +3409,23 @@ out:
 	mutex_unlock(&fs_info->qgroup_rescan_lock);
 
 	/*
-	 * only update status, since the previous part has already updated the
-	 * qgroup info.
+	 * Only update status, since the previous part has already updated the
+	 * qgroup info, and only if we did any actual work. This also prevents
+	 * race with a concurrent quota disable, which has already set
+	 * fs_info->quota_root to NULL and cleared BTRFS_FS_QUOTA_ENABLED at
+	 * btrfs_quota_disable().
 	 */
-	trans = btrfs_start_transaction(fs_info->quota_root, 1);
-	if (IS_ERR(trans)) {
-		err = PTR_ERR(trans);
+	if (did_leaf_rescans) {
+		trans = btrfs_start_transaction(fs_info->quota_root, 1);
+		if (IS_ERR(trans)) {
+			err = PTR_ERR(trans);
+			trans = NULL;
+			btrfs_err(fs_info,
+				  "fail to start transaction for status update: %d",
+				  err);
+		}
+	} else {
 		trans = NULL;
-		btrfs_err(fs_info,
-			  "fail to start transaction for status update: %d",
-			  err);
 	}
 
 	mutex_lock(&fs_info->qgroup_rescan_lock);