2022-10-02 9:21 GMT+09:00, Al Viro <viro@xxxxxxxxxxxxxxxxxx>:
> On Wed, Sep 21, 2022 at 07:43:37AM +0900, Namjae Jeon wrote:
>
>
> FWIW, it probably needs a few comments:
I will add it on next spin.
Thanks for your review!
>
> // c1 and p2 should be on the same fs
>> +struct dentry *lock_rename_child(struct dentry *c1, struct dentry *p2)
>> +{
>> + if (READ_ONCE(c1->d_parent) == p2) {
> // hopefully won't need to touch ->s_vfs_rename_mutex at all.
>> + inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
> // now that p2 is locked, nobody can move in or out of it,
> // so the test below is safe
>> + if (likely(c1->d_parent == p2))
>> + return NULL;
>> +
> // c1 got moved out of p2 while we'd been taking locks;
> // unlock and fall back to slow case
>> + inode_unlock(p2->d_inode);
>> + }
>> +
>> + mutex_lock(&c1->d_sb->s_vfs_rename_mutex);
> // nobody can move out of any directories on this fs
>> + if (likely(c1->d_parent != p2))
>> + return lock_two_directories(c1->d_parent, p2);
>> +
> // c1 got moved into p2 while we were taking locks;
> // we need p2 locked and ->s_vfs_rename_mutex unlocked,
> // for consistency with lock_rename().
>> + inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
>> + mutex_unlock(&c1->d_sb->s_vfs_rename_mutex);
>> + return NULL;
>> +}
>> +EXPORT_SYMBOL(lock_rename_child);
>
