Btrfs: fix possible empty list access when flushing the delalloc inodes

We didn't have a lock to protect the access to the delalloc inodes list, that is
we might access a empty delalloc inodes list if someone start flushing delalloc
inodes because the delalloc inodes were moved into a other list temporarily.
Fix it by wrapping the access with a lock.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index fbaf1ac3941b..0ec876657923 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8450,6 +8450,7 @@ static int __start_delalloc_inodes(struct btrfs_root *root, int delay_iput,
 	INIT_LIST_HEAD(&works);
 	INIT_LIST_HEAD(&splice);
 
+	mutex_lock(&root->delalloc_mutex);
 	spin_lock(&root->delalloc_lock);
 	list_splice_init(&root->delalloc_inodes, &splice);
 	while (!list_empty(&splice)) {
@@ -8495,6 +8496,7 @@ static int __start_delalloc_inodes(struct btrfs_root *root, int delay_iput,
 		list_splice_tail(&splice, &root->delalloc_inodes);
 		spin_unlock(&root->delalloc_lock);
 	}
+	mutex_unlock(&root->delalloc_mutex);
 	return ret;
 }
 
@@ -8536,6 +8538,7 @@ int btrfs_start_delalloc_roots(struct btrfs_fs_info *fs_info, int delay_iput,
 
 	INIT_LIST_HEAD(&splice);
 
+	mutex_lock(&fs_info->delalloc_root_mutex);
 	spin_lock(&fs_info->delalloc_root_lock);
 	list_splice_init(&fs_info->delalloc_roots, &splice);
 	while (!list_empty(&splice) && nr) {
@@ -8575,6 +8578,7 @@ out:
 		list_splice_tail(&splice, &fs_info->delalloc_roots);
 		spin_unlock(&fs_info->delalloc_root_lock);
 	}
+	mutex_unlock(&fs_info->delalloc_root_mutex);
 	return ret;
 }