On Wednesday, May 22, 2024 7:25:06 PM CEST Dominique Martinet wrote:
Christian Schoenebeck wrote on Wed, May 22, 2024 at 04:35:19PM +0200:
[...]
diff --git a/fs/9p/vfs_dentry.c b/fs/9p/vfs_dentry.c index f16f73581634..01338d4c2d9e 100644 --- a/fs/9p/vfs_dentry.c +++ b/fs/9p/vfs_dentry.c @@ -48,12 +48,17 @@ static int v9fs_cached_dentry_delete(const struct dentry *dentry) static void v9fs_dentry_release(struct dentry *dentry) { struct hlist_node *p, *n;
- struct hlist_head head;
p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p)\n", dentry, dentry);
- hlist_for_each_safe(p, n, (struct hlist_head *)&dentry->d_fsdata)
- spin_lock(&dentry->d_lock);
- hlist_move_list((struct hlist_head *)&dentry->d_fsdata, &head);
- spin_unlock(&dentry->d_lock);
- hlist_for_each_safe(p, n, &head) p9_fid_put(hlist_entry(p, struct p9_fid, dlist));
- dentry->d_fsdata = NULL;
}
I'm not sure if that works out. So you are moving the list from dentry to a local variable. But if you look at v9fs_fid_find() [fs/9p/fid.c#123] it reads dentry->d_fsdata (twice) and holds it as local variable before taking a lock. So the lock in v9fs_fid_find() should happen earlier, no?
The comment still works -- if detry->d_fsdata is NULL then hlist_for_each_entry will stop short and not iterate over anything (it won't bug out), so that part is fine in my opinion.
I meant the opposite: dentry->d_fsdata not being NULL. In this case v9fs_fid_find() takes a local copy of the list head pointer as `h` without taking a lock before.
Then v9fs_fid_find() takes the lock to run hlist_for_each_entry(), but at this point `h` could already point at garbage.
/Christian