Hello,
On (04/26/16 17:08), Dan Streetman wrote:
[..]
> -static void __zswap_pool_release(struct rcu_head *head)
> +static void __zswap_pool_release(struct work_struct *work)
> {
> - struct zswap_pool *pool = container_of(head, typeof(*pool), rcu_head);
> + struct zswap_pool *pool = container_of(work, typeof(*pool), work);
> +
> + synchronize_rcu();
>
> /* nobody should have been able to get a kref... */
> WARN_ON(kref_get_unless_zero(&pool->kref));
> @@ -674,7 +676,9 @@ static void __zswap_pool_empty(struct kref *kref)
> WARN_ON(pool == zswap_pool_current());
>
> list_del_rcu(&pool->list);
> - call_rcu(&pool->rcu_head, __zswap_pool_release);
> +
> + INIT_WORK(&pool->work, __zswap_pool_release);
> + schedule_work(&pool->work);
so in general the patch look good to me.
it's either I didn't have enough coffee yet (which is true) or
_IN THEORY_ it creates a tiny race condition; which is hard (and
unlikely) to hit, but still. and the problem being is
CONFIG_ZSMALLOC_STAT.
zsmalloc stats are exported via debugfs which is getting init
during pool set up in zs_pool_stat_create() -> debugfs_create_dir() zsmalloc<ID>.
so, once again, in theory, since zswap has the same <ID>, debugfs
dir will have the same for different pool, so a series of zpool
changes via user space knob
zsmalloc > zpool
zbud > zpool
zsmalloc > zpool
can result in
release zsmalloc0 switch to zbud switch to zsmalloc
__zswap_pool_release()
schedule_work()
...
zs_create_pool()
zs_pool_stat_create()
<< zsmalloc0 still exists >>
work is finally scheduled
zs_destroy_pool()
zs_pool_stat_destroy()
-ss
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