Btrfs: Add delayed iput

iput() can trigger new transactions if we are dropping the
final reference, so calling it in btrfs_commit_transaction
may end up deadlock. This patch adds delayed iput to avoid
the issue.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 53 insertions, 2 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 82740a3c628a..168e8c040aab 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2022,6 +2022,54 @@ zeroit:
         return -EIO;
 }
 
+struct delayed_iput {
+        struct list_head list;
+        struct inode *inode;
+};
+
+void btrfs_add_delayed_iput(struct inode *inode)
+{
+        struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
+        struct delayed_iput *delayed;
+
+        if (atomic_add_unless(&inode->i_count, -1, 1))
+                return;
+
+        delayed = kmalloc(sizeof(*delayed), GFP_NOFS | __GFP_NOFAIL);
+        delayed->inode = inode;
+
+        spin_lock(&fs_info->delayed_iput_lock);
+        list_add_tail(&delayed->list, &fs_info->delayed_iputs);
+        spin_unlock(&fs_info->delayed_iput_lock);
+}
+
+void btrfs_run_delayed_iputs(struct btrfs_root *root)
+{
+        LIST_HEAD(list);
+        struct btrfs_fs_info *fs_info = root->fs_info;
+        struct delayed_iput *delayed;
+        int empty;
+
+        spin_lock(&fs_info->delayed_iput_lock);
+        empty = list_empty(&fs_info->delayed_iputs);
+        spin_unlock(&fs_info->delayed_iput_lock);
+        if (empty)
+                return;
+
+        down_read(&root->fs_info->cleanup_work_sem);
+        spin_lock(&fs_info->delayed_iput_lock);
+        list_splice_init(&fs_info->delayed_iputs, &list);
+        spin_unlock(&fs_info->delayed_iput_lock);
+
+        while (!list_empty(&list)) {
+                delayed = list_entry(list.next, struct delayed_iput, list);
+                list_del(&delayed->list);
+                iput(delayed->inode);
+                kfree(delayed);
+        }
+        up_read(&root->fs_info->cleanup_work_sem);
+}
+
 /*
  * This creates an orphan entry for the given inode in case something goes
  * wrong in the middle of an unlink/truncate.
@@ -5568,7 +5616,7 @@ out_fail:
  * some fairly slow code that needs optimization. This walks the list
  * of all the inodes with pending delalloc and forces them to disk.
  */
-int btrfs_start_delalloc_inodes(struct btrfs_root *root)
+int btrfs_start_delalloc_inodes(struct btrfs_root *root, int delay_iput)
 {
         struct list_head *head = &root->fs_info->delalloc_inodes;
         struct btrfs_inode *binode;
@@ -5587,7 +5635,10 @@ int btrfs_start_delalloc_inodes(struct btrfs_root *root)
                 spin_unlock(&root->fs_info->delalloc_lock);
                 if (inode) {
                         filemap_flush(inode->i_mapping);
-                        iput(inode);
+                        if (delay_iput)
+                                btrfs_add_delayed_iput(inode);
+                        else
+                                iput(inode);
                 }
                 cond_resched();
                 spin_lock(&root->fs_info->delalloc_lock);