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>

3 files changed, 8 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 5f4921554f0a..2a9d32e193a5 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1490,6 +1490,7 @@ struct btrfs_fs_info {
          */
         struct list_head ordered_roots;
 
+        struct mutex delalloc_root_mutex;
         spinlock_t delalloc_root_lock;
         /* all fs/file tree roots that have delalloc inodes. */
         struct list_head delalloc_roots;
@@ -1805,6 +1806,7 @@ struct btrfs_root {
         spinlock_t root_item_lock;
         atomic_t refs;
 
+        struct mutex delalloc_mutex;
         spinlock_t delalloc_lock;
         /*
          * all of the inodes that have delalloc bytes.  It is possible for
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 237b5b5a2200..d9698fda2d12 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1221,6 +1221,7 @@ static void __setup_root(u32 nodesize, u32 leafsize, u32 sectorsize,
         mutex_init(&root->objectid_mutex);
         mutex_init(&root->log_mutex);
         mutex_init(&root->ordered_extent_mutex);
+        mutex_init(&root->delalloc_mutex);
         init_waitqueue_head(&root->log_writer_wait);
         init_waitqueue_head(&root->log_commit_wait[0]);
         init_waitqueue_head(&root->log_commit_wait[1]);
@@ -2209,6 +2210,7 @@ int open_ctree(struct super_block *sb,
         spin_lock_init(&fs_info->buffer_lock);
         rwlock_init(&fs_info->tree_mod_log_lock);
         mutex_init(&fs_info->reloc_mutex);
+        mutex_init(&fs_info->delalloc_root_mutex);
         seqlock_init(&fs_info->profiles_lock);
 
         init_completion(&fs_info->kobj_unregister);
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;
 }