* + mm-zswap-use-workqueue-to-destroy-pool.patch added to -mm tree
@ 2016-04-26 23:52 akpm
2016-04-27 5:40 ` Sergey Senozhatsky
0 siblings, 1 reply; 3+ messages in thread
From: akpm @ 2016-04-26 23:52 UTC (permalink / raw)
To: ddstreet, dan.streetman, yuzhao, mm-commits
The patch titled
Subject: mm/zswap: use workqueue to destroy pool
has been added to the -mm tree. Its filename is
mm-zswap-use-workqueue-to-destroy-pool.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-zswap-use-workqueue-to-destroy-pool.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-zswap-use-workqueue-to-destroy-pool.patch
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From: Dan Streetman <ddstreet@ieee.org>
Subject: 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 <ddstreet@ieee.org>
Reported-by: Yu Zhao <yuzhao@google.com>
Cc: Dan Streetman <dan.streetman@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/zswap.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff -puN mm/zswap.c~mm-zswap-use-workqueue-to-destroy-pool mm/zswap.c
--- a/mm/zswap.c~mm-zswap-use-workqueue-to-destroy-pool
+++ a/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(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));
@@ -674,7 +676,9 @@ 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 -mm which might be from ddstreet@ieee.org are
mm-zpool-use-workqueue-for-zpool_destroy.patch
mm-zswap-use-workqueue-to-destroy-pool.patch
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: + mm-zswap-use-workqueue-to-destroy-pool.patch added to -mm tree
2016-04-26 23:52 + mm-zswap-use-workqueue-to-destroy-pool.patch added to -mm tree akpm
@ 2016-04-27 5:40 ` Sergey Senozhatsky
2016-04-27 8:15 ` Dan Streetman
0 siblings, 1 reply; 3+ messages in thread
From: Sergey Senozhatsky @ 2016-04-27 5:40 UTC (permalink / raw)
To: akpm; +Cc: ddstreet, dan.streetman, yuzhao, mm-commits, linux-kernel
Hello,
On (04/26/16 16:52), akpm@linux-foundation.org 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 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 -mm which might be from ddstreet@ieee.org are
>
> mm-zpool-use-workqueue-for-zpool_destroy.patch
> mm-zswap-use-workqueue-to-destroy-pool.patch
I think only mm-zswap-use-workqueue-to-destroy-pool.patch is
needed.
-ss
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: + mm-zswap-use-workqueue-to-destroy-pool.patch added to -mm tree
2016-04-27 5:40 ` Sergey Senozhatsky
@ 2016-04-27 8:15 ` Dan Streetman
0 siblings, 0 replies; 3+ messages in thread
From: Dan Streetman @ 2016-04-27 8:15 UTC (permalink / raw)
To: Sergey Senozhatsky
Cc: Andrew Morton, Dan Streetman, Yu Zhao, mm-commits, linux-kernel
On Wed, Apr 27, 2016 at 1:40 AM, Sergey Senozhatsky
<sergey.senozhatsky.work@gmail.com> wrote:
> Hello,
>
> On (04/26/16 16:52), akpm@linux-foundation.org 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 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 -mm which might be from ddstreet@ieee.org are
>>
>> mm-zpool-use-workqueue-for-zpool_destroy.patch
>> mm-zswap-use-workqueue-to-destroy-pool.patch
>
> I think only mm-zswap-use-workqueue-to-destroy-pool.patch is
> needed.
yep, please drop mm-zpool-use-workqueue-for-zpool_destroy.patch
thanks!
>
> -ss
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2016-04-27 8:16 UTC | newest]
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2016-04-26 23:52 + mm-zswap-use-workqueue-to-destroy-pool.patch added to -mm tree akpm
2016-04-27 5:40 ` Sergey Senozhatsky
2016-04-27 8:15 ` Dan Streetman
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