Function xx causes a deadlock，because s_vfs_rename_mutex was not released when return
Signed-off-by: Li Dong <[email protected]>
---
fs/namei.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/namei.c b/fs/namei.c
index 91171da719c5..63b3fd05fef2 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3076,8 +3076,10 @@ struct dentry *lock_rename_child(struct dentry *c1, struct dentry *p2)
/*
* nobody can move out of any directories on this fs.
*/
- if (likely(c1->d_parent != p2))
+ if (likely(c1->d_parent != p2)) {
+ mutex_unlock(&c1->d_sb->s_vfs_rename_mutex);
return lock_two_directories(c1->d_parent, p2);
+ }
/*
* c1 got moved into p2 while we were taking locks;
--
2.31.1.windows.1
On Mon, Jun 19, 2023 at 09:37:14PM +0800, Li Dong wrote:
> Function xx causes a deadlock，because s_vfs_rename_mutex was not released when return
>
> Signed-off-by: Li Dong <[email protected]>
> ---
This is a cross-directory rename which requires s_vfs_rename_mutex to be
held. You're suggesting to drop it, violating basic locking assumptions
with dire consequences:
lock_rename_child()
{
c1->d_parent != p2
-> acquire s_vfs_rename_mutex
}
pairs with
old_parent = c1->d_parent;
unlock_rename(old_parent, p2)
{
if (old_parent != p2)
-> release s_vfs_rename_mutex
}
See the usage in ksmbd:
trap = lock_rename_child(old_child, new_path.dentry);
old_parent = dget(old_child->d_parent);
unlock_rename(old_parent, new_path.dentry);