[PATCH 2/2] fuse: fix invalidate lock leak on open O_TRUNC DAX failure

[Baokun Li]

fuse_open() takes filemap_invalidate_lock() for a DAX truncate
(dax_truncate = true) and releases it before the out_inode_unlock
label.  But when fuse_dax_break_layouts() fails, the goto
out_inode_unlock skips the unlock and leaks the rwsem, so any later
fault or truncate on the file stalls on the stale lock.

fuse_dax_break_layouts() can fail with -ERESTARTSYS when a signal
interrupts the wait for busy DAX pages to drain:

  open("file", O_RDWR | O_TRUNC)
  └─ fuse_open()
     ├─ filemap_invalidate_lock()        # dax_truncate
     └─ fuse_dax_break_layouts()
        └─ dax_break_layout()
           └─ wait_page_idle()           # TASK_INTERRUPTIBLE
              └─ fuse_wait_dax_page()    # unlock, schedule, re-lock
                 └─ signal → -ERESTARTSYS
     goto out_inode_unlock               # <- lock leaked

Fix this by moving filemap_invalidate_unlock() below the label so
that all error paths release the lock, and rename the label to
out_unlock as it now covers more than just the inode lock.

Fixes: 2fdbb8dd0155 ("fuse: fix deadlock between atomic O_TRUNC and page invalidation")
Cc: <stable@xxxxxxxxxxxxxxx> # v6.0+
Signed-off-by: Baokun Li <libaokun@xxxxxxxxxxxxxxxxx>
---
 fs/fuse/file.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index ceada75310b8..e7b2a839f081 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -272,7 +272,7 @@ static int fuse_open(struct inode *inode, struct file *file)
 		filemap_invalidate_lock(inode->i_mapping);
 		err = fuse_dax_break_layouts(inode, 0, -1);
 		if (err)
-			goto out_inode_unlock;
+			goto out_unlock;
 	}
 
 	if (is_wb_truncate || dax_truncate)
@@ -296,9 +296,9 @@ static int fuse_open(struct inode *inode, struct file *file)
 		else if (!(ff->open_flags & FOPEN_KEEP_CACHE))
 			invalidate_inode_pages2(inode->i_mapping);
 	}
+out_unlock:
 	if (dax_truncate)
 		filemap_invalidate_unlock(inode->i_mapping);
-out_inode_unlock:
 	if (is_wb_truncate || dax_truncate)
 		inode_unlock(inode);
 
-- 
2.43.7