[PATCH 5.10.y] fuse: fix invalidate lock leak on open O_TRUNC DAX failure

[Sasha Levin <sashal@kernel.org>]

From: Baokun Li <libaokun@linux.alibaba.com>

[ Upstream commit a927f1867e61b78f39f9da0bbba3c98c2ca151fe ]

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@vger.kernel.org # v6.0+
Signed-off-by: Baokun Li <libaokun@linux.alibaba.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
[ changed goto target from out_inode_unlock to out_unlock and relocated the out_unlock label before up_write() on i_mmap_sem, adapting the fix from filemap_invalidate_lock/unlock and fuse_open() to 5.10's i_mmap_sem/down_write/up_write and fuse_open_common() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/fuse/file.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index a8c080b485d03..a8678753b2d33 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -239,7 +239,7 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
 		down_write(&get_fuse_inode(inode)->i_mmap_sem);
 		err = fuse_dax_break_layouts(inode, 0, 0);
 		if (err)
-			goto out_inode_unlock;
+			goto out_unlock;
 	}
 
 	if (is_wb_truncate || dax_truncate)
@@ -259,10 +259,9 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
 		else if (!(ff->open_flags & FOPEN_KEEP_CACHE))
 			invalidate_inode_pages2(inode->i_mapping);
 	}
+out_unlock:
 	if (dax_truncate)
 		up_write(&get_fuse_inode(inode)->i_mmap_sem);
-
-out_inode_unlock:
 	if (is_wb_truncate || dax_truncate)
 		inode_unlock(inode);
 
-- 
2.53.0