Re: [PATCH 1/1] kasan: fix livelock in qlist_move_cache

[Zhouyi Zhou <zhouzhouyi@gmail.com>]

Thanks for reviewing
   My machine has 128G of RAM, and runs many KVM virtual machines.
libvirtd always
report "internal error: received hangup / error event on socket" under
heavy memory load.
   Then I use perf top -g, qlist_move_cache consumes 100% cpu for
several minutes.

On Tue, Nov 28, 2017 at 3:45 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Tue, Nov 28, 2017 at 5:05 AM, Zhouyi Zhou <zhouzhouyi@gmail.com> wrote:
>> When there are huge amount of quarantined cache allocates in system,
>> number of entries in global_quarantine[i] will be great. Meanwhile,
>> there is no relax in while loop in function qlist_move_cache which
>> hold quarantine_lock. As a result, some userspace programs for example
>> libvirt will complain.
>
> Hi,
>
> The QUARANTINE_BATCHES thing was supposed to fix this problem, see
> quarantine_remove_cache() function.
> What is the amount of RAM and number of CPUs in your system?
> If system has 4GB of RAM, quarantine size is 128MB and that's split
> into 1024 batches. Batch size is 128KB. Even if that's filled with the
> smallest objects of size 32, that's only 4K objects. And there is a
> cond_resched() between processing of every batch.
> I don't understand why it causes problems in your setup. We use KASAN
> extremely heavily on hundreds of machines 24x7 and we have not seen
> any single report from this code...
>
>
>> On Tue, Nov 28, 2017 at 12:04 PM,  <zhouzhouyi@gmail.com> wrote:
>>> From: Zhouyi Zhou <zhouzhouyi@gmail.com>
>>>
>>> This patch fix livelock by conditionally release cpu to let others
>>> has a chance to run.
>>>
>>> Tested on x86_64.
>>> Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
>>> ---
>>>  mm/kasan/quarantine.c | 12 +++++++++++-
>>>  1 file changed, 11 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
>>> index 3a8ddf8..33eeff4 100644
>>> --- a/mm/kasan/quarantine.c
>>> +++ b/mm/kasan/quarantine.c
>>> @@ -265,10 +265,13 @@ static void qlist_move_cache(struct qlist_head *from,
>>>                                    struct kmem_cache *cache)
>>>  {
>>>         struct qlist_node *curr;
>>> +       struct qlist_head tmp_head;
>>> +       unsigned long flags;
>>>
>>>         if (unlikely(qlist_empty(from)))
>>>                 return;
>>>
>>> +       qlist_init(&tmp_head);
>>>         curr = from->head;
>>>         qlist_init(from);
>>>         while (curr) {
>>> @@ -278,10 +281,17 @@ static void qlist_move_cache(struct qlist_head *from,
>>>                 if (obj_cache == cache)
>>>                         qlist_put(to, curr, obj_cache->size);
>>>                 else
>>> -                       qlist_put(from, curr, obj_cache->size);
>>> +                       qlist_put(&tmp_head, curr, obj_cache->size);
>>>
>>>                 curr = next;
>>> +
>>> +               if (need_resched()) {
>>> +                       spin_unlock_irqrestore(&quarantine_lock, flags);
>>> +                       cond_resched();
>>> +                       spin_lock_irqsave(&quarantine_lock, flags);
>>> +               }
>>>         }
>>> +       qlist_move_all(&tmp_head, from);
>>>  }
>>>
>>>  static void per_cpu_remove_cache(void *arg)
>>> --
>>> 2.1.4
>>>
>>
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