Re: [PATCH] mm: vmscan: make unregister_shrinker() safer

[ak <akaraliou.dev@gmail.com>]

On 12/18/2017 11:49 AM, Michal Hocko wrote:

> On Sat 16-12-17 22:29:37, Aliaksei Karaliou wrote:
>> unregister_shrinker() does not have any sanitizing inside so
>> calling it twice will oops because of double free attempt or so.
>> This patch makes unregister_shrinker() safer and allows calling
>> it on resource freeing path without explicit knowledge of whether
>> shrinker was successfully registered or not.
> Tetsuo has made it half way to this already [1]. So maybe we should
> fold shrinker->nr_deferred = NULL to his patch and finally merge it.
>
> [1] http://lkml.kernel.org/r/1511523385-6433-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
Yeah, no problem from my side.
I'm sorry, it seems that I haven't done enough research to realize that 
someone is already
looking at that place.


The only my concern/question is whether we should also add some paranoid 
stuff in that
extra branch (check that list is empty for example) or not.
>> Signed-off-by: Aliaksei Karaliou <akaraliou.dev@gmail.com>
>> ---
>>   mm/vmscan.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 65c4fa26abfa..7cb56db5e9ca 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -281,10 +281,14 @@ EXPORT_SYMBOL(register_shrinker);
>>    */
>>   void unregister_shrinker(struct shrinker *shrinker)
>>   {
>> +	if (!shrinker->nr_deferred)
>> +		return;
>> +
>>   	down_write(&shrinker_rwsem);
>>   	list_del(&shrinker->list);
>>   	up_write(&shrinker_rwsem);
>>   	kfree(shrinker->nr_deferred);
>> +	shrinker->nr_deferred = NULL;
>>   }
>>   EXPORT_SYMBOL(unregister_shrinker);
>>   
>> -- 
>> 2.11.0
>>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>