From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:57118 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933308AbeAKOFE (ORCPT ); Thu, 11 Jan 2018 09:05:04 -0500 Subject: Patch "mm/zswap: use workqueue to destroy pool" has been added to the 4.4-stable tree To: ddstreet@ieee.org, akpm@linux-foundation.org, dan.streetman@canonical.com, gregkh@linuxfoundation.org, minchan@kernel.org, sergey.senozhatsky@gmail.com, torvalds@linux-foundation.org, vbabka@suse.cz, yuzhao@google.com Cc: , From: Date: Thu, 11 Jan 2018 15:04:49 +0100 Message-ID: <151567948973189@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled mm/zswap: use workqueue to destroy pool to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: mm-zswap-use-workqueue-to-destroy-pool.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 200867af4dedfe7cb707f96773684de1d1fd21e6 Mon Sep 17 00:00:00 2001 From: Dan Streetman Date: Fri, 20 May 2016 16:59:54 -0700 Subject: mm/zswap: use workqueue to destroy pool From: Dan Streetman commit 200867af4dedfe7cb707f96773684de1d1fd21e6 upstream. 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") Signed-off-by: Dan Streetman Reported-by: Yu Zhao Reviewed-by: Sergey Senozhatsky Cc: Minchan Kim Cc: Dan Streetman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Vlastimil Babka Signed-off-by: Greg Kroah-Hartman --- mm/zswap.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) --- a/mm/zswap.c +++ b/mm/zswap.c @@ -123,7 +123,7 @@ 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]; }; @@ -667,9 +667,11 @@ static int __must_check zswap_pool_get(s 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)); @@ -689,7 +691,9 @@ static void __zswap_pool_empty(struct kr 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); } Patches currently in stable-queue which might be from ddstreet@ieee.org are queue-4.4/mm-zswap-use-workqueue-to-destroy-pool.patch queue-4.4/zswap-don-t-param_set_charp-while-holding-spinlock.patch