path: root/mm/zswap.c
diff options
authorDan Streetman <>2016-05-20 16:59:54 -0700
committerLinus Torvalds <>2016-05-20 17:58:30 -0700
commit200867af4dedfe7cb707f96773684de1d1fd21e6 (patch)
tree9c83c54dd822d1f928587c24e608accbccb27c9b /mm/zswap.c
parentda9556a2367cf2261ab4d3e100693c82fb1ddb26 (diff)
mm/zswap: use workqueue to destroy pool
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 <>
Diffstat (limited to 'mm/zswap.c')
1 files changed, 8 insertions, 4 deletions
diff --git a/mm/zswap.c b/mm/zswap.c
index de0f119b1780..275b22cc8df4 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];
@@ -658,9 +658,11 @@ 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... */
@@ -680,7 +682,9 @@ static void __zswap_pool_empty(struct kref *kref)
WARN_ON(pool == zswap_pool_current());
- call_rcu(&pool->rcu_head, __zswap_pool_release);
+ INIT_WORK(&pool->work, __zswap_pool_release);
+ schedule_work(&pool->work);