On Thu, Oct 26, 2017 at 04:48:54PM -0700, Andi Kleen wrote:
> static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
> struct shrink_control *sc)
> {
> + struct list_head *tmp, *pos;
> unsigned long ret;
> + LIST_HEAD(nodes);
> + spinlock_t *lock = NULL;
>
> - /* list_lru lock nests inside IRQ-safe mapping->tree_lock */
> + ret = list_lru_shrink_walk(&shadow_nodes, sc, shadow_lru_isolate, &nodes);
> local_irq_disable();
> - ret = list_lru_shrink_walk(&shadow_nodes, sc, shadow_lru_isolate, NULL);
> + list_for_each_safe (pos, tmp, &nodes)
> + free_shadow_node(pos, &lock);
The nlru->lock in list_lru_shrink_walk() is the only thing that keeps
truncation blocked on workingset_update_node() -> list_lru_del() and
so ultimately keeping it from freeing the radix tree node.
It's not safe to access the nodes on the private list after that.
Batching mapping->tree_lock is possible, but you have to keep the
lock-handoff scheme. Pass a &mapping to list_lru_shrink_walk() and
only unlock and spin_trylock(&mapping->tree_lock) if it changes?
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