2022-04-01 22:34 GMT+09:00, Al Viro <viro@xxxxxxxxxxxxxxxxxx>:
> On Fri, Apr 01, 2022 at 09:52:09PM +0900, Namjae Jeon wrote:
>> > take source and new parent and do the following:
>> >
>> > if (READ_ONCE(source->d_parent) == new_parent) {
>> > inode_lock_nested(new_parent->d_inode, I_MUTEX_PARENT);
>> > if (likely(source->d_parent == new_parent))
>> > return NULL;
> and
> inode_unlock(new_parent->d_inode);
> to do locking in proper order...
Okay, Let me check it with these codes.
Thanks for sharing the codes!
>
>> > }
>> > // fuck that, looks like a cross-rename one.
>> > mutex_lock(&source->d_sb->s_vfs_rename_mutex);
>> > // now all ->d_parent are stable
>> > if (unlikely(source->d_parent == new_parent)) {
>> > inode_lock_nested(new_parent->d_inode, I_MUTEX_PARENT);
>> > // we want the same rules as for lock_rename()
>> > mutex_unlock(&source->d_sb->s_vfs_rename_mutex);
>> > return NULL;
>> > }
>> > // cross-directory it is...
>> > same as lock_rename() after having grabbed ->s_vfs_rename_mutex
>
> // p1 != p2, p1->d_sb == p2->d_sb, p1->d_sb->s_vfs_rename_mutex held
> static struct dentry *lock_two_directories(struct dentry *p1, struct dentry
> *p2)
> {
> struct dentry *p;
>
> p = d_ancestor(p2, p1);
> if (p) {
> inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
> inode_lock_nested(p1->d_inode, I_MUTEX_CHILD);
> return p;
> }
>
> p = d_ancestor(p1, p2);
> if (p) {
> inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
> inode_lock_nested(p2->d_inode, I_MUTEX_CHILD);
> return p;
> }
>
> inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
> inode_lock_nested(p2->d_inode, I_MUTEX_PARENT2);
> return NULL;
> }
>
> struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
> {
> if (p1 == p2) {
> inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
> return NULL;
> }
>
> mutex_lock(&p1->d_sb->s_vfs_rename_mutex);
> return lock_two_directories(p1, p2);
> }
>
> struct dentry *lock_rename_child(struct dentry *c1, struct dentry *p2)
> {
> if (READ_ONCE(c1->d_parent) == p2) {
> inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
> if (likely(c1->d_parent == p2))
> return NULL;
>
> // too bad, we'd raced with another rename
> inode_unlock(p2->d_inode);
> }
>
> // looks like it's cross-directory
> mutex_lock(&c1->d_sb->s_vfs_rename_mutex);
>
> // recheck, now that ->d_parent is stable
> if (likely(c1->d_parent != p2))
> return lock_two_directories(c1->d_parent, p2);
>
> // it's not cross-directory, after all - raced with another rename
> inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
> // drop ->s_vfs_rename_mutex, so we won't confuse unlock_rename()
> // note that locked p2 alone is enough to prevent moves to or from
> // p2, so c1->d_parent will remain p2 until we unlock p2
> mutex_unlock(&c1->d_sb->s_vfs_rename_mutex);
> return NULL;
> }
>
