[PATCH 2/3] fs/libfs.c: use 'spin_lock_nested' when taking 'd_lock' for dentry in simple_empty

yu kuai
2019-11-15T03:20:41Z

simple_emtpty currently use 'spin_lock_nested' for 'child' to avoid
confusion for lockdep. However, it's not used for 'dentry'.

In that case, there will be a problem if the caller called 'simple_empty'
with a parent's 'd_lock' held:

spin_lock(&dentry->d_parent->d_lock)
call simple_empty(dentry)
spin_lock(&dentry->d_lock) --> lockdep will report this
spin_lock_nested(child->d_lock, spin_lock_nested)
spin_unlock(child_lock)
spin_unlock($dentry->d_lock)
return from simple_empty
spin_unlock(&dentry->d_patrent->d_lock)

So, use 'DENTRY_D_LOCK_NESTED' for 'dentry' and 'spin_lock_nested_2' for
child.

Signed-off-by: yu kuai <yukuai3@huawei.com>
---
fs/libfs.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index 1463b03..62e9ba9 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -336,9 +336,9 @@ int simple_empty(struct dentry *dentry)
struct dentry *child;
int ret = 0;

- spin_lock(&dentry->d_lock);
+ spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
list_for_each_entry(child, &dentry->d_subdirs, d_child) {
- spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
+ spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED_2);
if (simple_positive(child)) {
spin_unlock(&child->d_lock);
goto out;
--
2.7.4