ocfs2: avoid potential ABBA deadlock by reordering tl_inode lock

In ocfs2_move_extent(), tl_inode is currently locked after the global
bitmap inode.  However, in ocfs2_flush_truncate_log(), the lock order is
reversed: tl_inode is locked first, followed by the global bitmap inode.

This creates a classic ABBA deadlock scenario if two threads attempt these
operations concurrently and acquire the locks in different orders.

To prevent this, move the tl_inode locking earlier in ocfs2_move_extent(),
so that it always precedes the global bitmap inode lock.

No functional changes beyond lock ordering.

Link: https://lkml.kernel.org/r/20250708020640.387741-1-ipravdin.official@gmail.com
Reported-by: syzbot+6bf948e47f9bac7aacfa@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/67d5645c.050a0220.1dc86f.0004.GAE@google.com/
Signed-off-by: Ivan Pravdin <ipravdin.official@gmail.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/ocfs2/move_extents.c b/fs/ocfs2/move_extents.c
index 369c7d27befd9c706a23be0649d1ab216ab43f81..cbe2f8ed88974f81e97d95dae1e129bb6a89885c 100644 (file)
--- a/fs/ocfs2/move_extents.c
+++ b/fs/ocfs2/move_extents.c
@@ -617,6 +617,8 @@ static int ocfs2_move_extent(struct ocfs2_move_extents_context *context,
         */
        credits += OCFS2_INODE_UPDATE_CREDITS + 1;
 
+       inode_lock(tl_inode);
+
        /*
         * ocfs2_move_extent() didn't reserve any clusters in lock_allocators()
         * logic, while we still need to lock the global_bitmap.
@@ -626,7 +628,7 @@ static int ocfs2_move_extent(struct ocfs2_move_extents_context *context,
        if (!gb_inode) {
                mlog(ML_ERROR, "unable to get global_bitmap inode\n");
                ret = -EIO;
-               goto out;
+               goto out_unlock_tl_inode;
        }
 
        inode_lock(gb_inode);
@@ -634,16 +636,14 @@ static int ocfs2_move_extent(struct ocfs2_move_extents_context *context,
        ret = ocfs2_inode_lock(gb_inode, &gb_bh, 1);
        if (ret) {
                mlog_errno(ret);
-               goto out_unlock_gb_mutex;
+               goto out_unlock_gb_inode;
        }
 
-       inode_lock(tl_inode);
-
        handle = ocfs2_start_trans(osb, credits);
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                mlog_errno(ret);
-               goto out_unlock_tl_inode;
+               goto out_unlock;
        }
 
        new_phys_blkno = ocfs2_clusters_to_blocks(inode->i_sb, *new_phys_cpos);
@@ -703,15 +703,14 @@ static int ocfs2_move_extent(struct ocfs2_move_extents_context *context,
 out_commit:
        ocfs2_commit_trans(osb, handle);
        brelse(gd_bh);
-
-out_unlock_tl_inode:
-       inode_unlock(tl_inode);
-
+out_unlock:
        ocfs2_inode_unlock(gb_inode, 1);
-out_unlock_gb_mutex:
+out_unlock_gb_inode:
        inode_unlock(gb_inode);
        brelse(gb_bh);
        iput(gb_inode);
+out_unlock_tl_inode:
+       inode_unlock(tl_inode);
 
 out:
        if (context->meta_ac) {