PR_GROWINGNOWAIT useless ?

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

Hello,
while investigating the deadlock reported in
https://mail-index.netbsd.org/tech-kern/2025/05/05/msg030407.html
I looked at pool_grow(). It seems that the PR_GROWINGNOWAIT is used only for
this:
                        if (pp->pr_flags & PR_GROWINGNOWAIT) {
                                /*
                                 * This needs an unlock/relock dance so
                                 * that the other caller has a chance to
                                 * run and actually do the thing.  Note 
                                 * that this is effectively a busy-wait.
                                 */  
                                mutex_exit(&pp->pr_lock);
                                mutex_enter(&pp->pr_lock);
                                return ERESTART;
                        }

but as I understand it, the thread setting PR_GROWINGNOWAIT in pool_grow()
is holding the pr_lock and will never release it before clearing
PR_GROWINGNOWAIT. If pool_allocator_alloc() or pool_alloc_item_header()
was releasing the lock, it would have to eventually sleep to reaquire
it and it's not allowed without PR_WAITOK.
So it seems that PR_GROWINGNOWAIT could be removed.

Did I miss something ?

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--