2016-08-10 13:36 GMT+02:00 Roman Penyaev <roman.penyaev@xxxxxxxxxxxxxxxx>:
> On Wed, Aug 10, 2016 at 10:42 AM, Roman Penyaev
> <roman.penyaev@xxxxxxxxxxxxxxxx> wrote:
>> Hi,
>>
>> On Wed, Aug 10, 2016 at 5:55 AM, Tejun Heo <tj@xxxxxxxxxx> wrote:
>>> Hello,
>>>
>>> On Mon, Aug 08, 2016 at 01:39:08PM +0200, Roman Pen wrote:
>>>> Long time ago there was a similar fix proposed by Akinobu Mita[1],
>>>> but it seems that time everyone decided to fix this subtle race in
>>>> percpu-refcount and Tejun Heo[2] did an attempt (as I can see that
>>>> patchset was not applied).
>>>
>>> So, I probably forgot about it while waiting for confirmation of fix.
>>> Can you please verify that the patchset fixes the issue? I can apply
>>> the patchset right away.
>>
>> I have not checked your patchset but according to my understanding
>> it should not fix *this* issue.
>
> So, your patchset does not help (but for sure it helps for keeping
> internal percpu-refcount members consistent, but that is not related
> to this issue). That's the backtrace which I observe:
>
> Call Trace:
> [<ffffffff810ba8df>] ? vprintk_default+0x1f/0x30
> [<ffffffff816a47f5>] schedule+0x35/0x80
> [<ffffffff81336154>] blk_mq_freeze_queue_wait+0x124/0x1a0
> [<ffffffff810a3f70>] ? wake_atomic_t_function+0x60/0x60
> [<ffffffff8133821a>] blk_mq_freeze_queue+0x1a/0x20
> [<ffffffff8133822e>] blk_freeze_queue+0xe/0x10
> [<ffffffff81329cc2>] blk_cleanup_queue+0xe2/0x280
>
> To ease reproduction I do the following:
>
> -------------------------------------------
> static int thread_fn(void *data)
> {
> struct blk_mq_tag_set *tags = data;
> struct request_queue *q;
>
> while (!kthread_should_stop()) {
> q = blk_mq_init_queue(tags);
> BUG_ON(q == NULL);
> /*
> * That is done by blk_register_queue(), but here
> * we are reproducing blk-mq bug and do not require
> * gendisk and friends. Just silently switch to percpu.
> */
> percpu_ref_switch_to_percpu(&q->q_usage_counter);
>
> msleep(prandom_u32_max(10));
> blk_cleanup_queue(q);
> }
>
> return 0;
> }
> -------------------------------------------
>
> o Start 2 threads (exactly 2, we need 2 queues for 1 shared tags)
> o Pass same shared tags pointer for each thread
> o Wait
> o PROFIT
>
> To make immediate reproduction this hunk can be applied:
>
> @@ -129,6 +142,7 @@ void blk_mq_unfreeze_queue(struct request_queue *q)
> freeze_depth = atomic_dec_return(&q->mq_freeze_depth);
> WARN_ON_ONCE(freeze_depth < 0);
> if (!freeze_depth) {
> + msleep(1000);
> percpu_ref_reinit(&q->q_usage_counter);
> wake_up_all(&q->mq_freeze_wq);
> }
>
> --
> Roman
Hi Jens,
I didn't see this patch in you tree, what's the blocker?
Thanks,
Jinpu
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