Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753283AbcDZVKZ (ORCPT ); Tue, 26 Apr 2016 17:10:25 -0400 Received: from mail-qg0-f66.google.com ([209.85.192.66]:36347 "EHLO mail-qg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752688AbcDZVKT (ORCPT ); Tue, 26 Apr 2016 17:10:19 -0400 From: Dan Streetman To: Yu Zhao , Andrew Morton , Seth Jennings Cc: Sergey Senozhatsky , Minchan Kim , Nitin Gupta , Linux-MM , Sergey Senozhatsky , linux-kernel , Dan Streetman , Dan Streetman Subject: [PATCH] mm/zswap: use workqueue to destroy pool Date: Tue, 26 Apr 2016 17:08:11 -0400 Message-Id: <1461704891-15272-1-git-send-email-ddstreet@ieee.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1461619210-10057-1-git-send-email-ddstreet@ieee.org> References: <1461619210-10057-1-git-send-email-ddstreet@ieee.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2949 Lines: 89 Add a work_struct to struct zswap_pool, and change __zswap_pool_empty to use the workqueue instead of using call_rcu(). When zswap destroys a pool no longer in use, it uses call_rcu() to perform the destruction/freeing. Since that executes in softirq context, it must not sleep. However, actually destroying the pool involves freeing the per-cpu compressors (which requires locking the cpu_add_remove_lock mutex) and freeing the zpool, for which the implementation may sleep (e.g. zsmalloc calls kmem_cache_destroy, which locks the slab_mutex). So if either mutex is currently taken, or any other part of the compressor or zpool implementation sleeps, it will result in a BUG(). It's not easy to reproduce this when changing zswap's params normally. In testing with a loaded system, this does not fail: $ cd /sys/module/zswap/parameters $ echo lz4 > compressor ; echo zsmalloc > zpool nor does this: $ while true ; do > echo lzo > compressor ; echo zbud > zpool > sleep 1 > echo lz4 > compressor ; echo zsmalloc > zpool > sleep 1 > done although it's still possible either of those might fail, depending on whether anything else besides zswap has locked the mutexes. However, changing a parameter with no delay immediately causes the schedule while atomic BUG: $ while true ; do > echo lzo > compressor ; echo lz4 > compressor > done This is essentially the same as Yu Zhao's proposed patch to zsmalloc, but moved to zswap, to cover compressor and zpool freeing. Fixes: f1c54846ee45 ("zswap: dynamic pool creation") Reported-by: Yu Zhao Signed-off-by: Dan Streetman Cc: Dan Streetman --- mm/zswap.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index 91dad80..f207da7 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -117,7 +117,7 @@ struct zswap_pool { struct crypto_comp * __percpu *tfm; struct kref kref; struct list_head list; - struct rcu_head rcu_head; + struct work_struct work; struct notifier_block notifier; char tfm_name[CRYPTO_MAX_ALG_NAME]; }; @@ -652,9 +652,11 @@ static int __must_check zswap_pool_get(struct zswap_pool *pool) return kref_get_unless_zero(&pool->kref); } -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); spin_unlock(&zswap_pools_lock); } -- 2.7.4