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better lockdep annotations for simple_recursive_removal()

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[ Upstream commit 2a8061ee5e ]

We want a class that nests outside of I_MUTEX_NORMAL (for the sake of
callbacks that might want to lock the victim) and inside I_MUTEX_PARENT
(so that a variant of that could be used with parent of the victim
held locked by the caller).

In reality, simple_recursive_removal()
	* never holds two locks at once
	* holds the lock on parent of dentry passed to callback
	* is used only on the trees with fixed topology, so the depths
are not changing.

So the locking order is actually fine.

AFAICS, the best solution is to assign I_MUTEX_CHILD to the locks
grabbed by that thing.

Reported-by: syzbot+169de184e9defe7fe709@syzkaller.appspotmail.com
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Al Viro 2025-07-02 22:30:32 -04:00 committed by Greg Kroah-Hartman
parent ad5f53b993
commit 11b567346c
1 changed files with 2 additions and 2 deletions
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4
fs/libfs.c
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@ -273,7 +273,7 @@ void simple_recursive_removal(struct dentry *dentry,
struct dentry *victim = NULL, *child;
struct inode *inode = this->d_inode;
inode_lock(inode);
inode_lock_nested(inode, I_MUTEX_CHILD);
if (d_is_dir(this))
inode->i_flags |= S_DEAD;
while ((child = find_next_child(this, victim)) == NULL) {
@ -285,7 +285,7 @@ void simple_recursive_removal(struct dentry *dentry,
victim = this;
this = this->d_parent;
inode = this->d_inode;
inode_lock(inode);
inode_lock_nested(inode, I_MUTEX_CHILD);
if (simple_positive(victim)) {
d_invalidate(victim); // avoid lost mounts
if (d_is_dir(victim))