On Fri, Feb 23, 2018 at 12:13 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> Look:
> dentry placed on a shrink list
> we pick the fucker from the list and lock it.
> we call lock_parent() on it.
> dentry is not a root and it's not deleted, so we proceed.
> trylock fails.
> we grab rcu_read_lock()
> we drop dentry->d_lock
[ deleted the bad things ]
Should we just instead get the ref to the dentry before dropping the
lock, so that nobody else can get to dentry_kill?
This is too subtle, and your fix to check d_lockref.count < 0 sounds
wrong to me. If it's really gone, maybe it has been reused and the
refcount is positive again, but it's something else than a dentry
entirely?
Hmm.
No, you extended the rcu read section, so I guess your patch is fine.
And lock_parent already has that pattern, soiit's not new.
Ok, I agree, looks like lock_parent should just re-check that thing
that it already checked earler, but that now might be true again
because of we dropped d_lock.
Linus
