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Subject: Re: [PATCH] autofs4: use wake_up() instead of wake_up_interruptible
To:     Andrei Vagin <avagin@virtuozzo.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Andrei Vagin <avagin@openvz.org>, autofs@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Matthew Wilcox <mawilcox@microsoft.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>
References: <20180331022839.21277-1-avagin@openvz.org>
 <ebdc431d-cea8-378c-aae5-3b7441bb93c0@themaw.net>
 <8d578e49-c1a0-a38d-3b91-f0a07de0089b@themaw.net>
 <20180401062117.GA27067@outlook.office365.com>
From:   Ian Kent <raven@themaw.net>
Message-ID: <46f1c699-21bd-3615-0d2c-52ea3ac565e2@themaw.net>
Date:   Tue, 3 Apr 2018 07:39:33 +0800
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On 01/04/18 14:21, Andrei Vagin wrote:
> On Sun, Apr 01, 2018 at 10:01:41AM +0800, Ian Kent wrote:
>> On 01/04/18 09:31, Ian Kent wrote:
>>> On 31/03/18 10:28, Andrei Vagin wrote:
>>>> In "autofs4: use wait_event_killable",  wait_event_interruptible() was
>>>> replaced by wait_event_killable(), but in this case we have to use
>>>> wake_up() instead of wake_up_interruptible().
>>>
>>> Why do you believe wake_up() is needed rather than wake_up_interruptible()?
>>>
>>> Now that I'm thinking about the wake up I'm wondering if this is in fact
>>> what's needed. Rather, I think maybe wake_up_all() is probably the only
>>> one that will actually do what's needed.
>>
>> Ok, so that 1 is the number of exclusive waiters.
>> So what is the difference between the two wake_up calls in this case?
> 
> In CRIU, we have the autofs test:
> https://github.com/checkpoint-restore/criu/blob/master/test/zdtm/static/autofs.c
> 
> We run CRIU tests on the linux-next kernels and a few days ago this test
> started to fail, actually it hangs up.
> 
> I found that wake_up_interruptible() doesn't wake up a thread, which is
> waiting.
> 
> try_to_wake_up() has the argument "state", it is the mask of task states
> that can be woken.
> 
> For wake_up_interruptible(), state is TASK_INTERRUPTIBLE.
> For wake_up(). state is TASK_NORMAL (TASK_INTERRUPTIBLE | TASK_UNINTERRUPTIBLE)
> 
> If we use wait_event_killable(), the task sleeps in the TASK_KILLABLE
> state, so wake_up_interruptible() isn't suitable in this case.
> 
> #define TASK_KILLABLE                   (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
> 
> I checked that our test passes with this patch. I mean that we had a
> real problem and we checked that it is fixed by this patch.

Ahh, I see, wake_up_*() functions do just what they say, they skip
TASK_UNINTERRUPTIBLE tasks.

Now it makes sense.

Acked-by: Ian Kent <raven@themaw.net>

Andrew could you a take this patch as well please.

> 
> Thanks,
> Andrei
> 
>>
>>>
>>> There's an individual wait queue for each mount, there can be multiple
>>> waiters for a mount, they all should be woken up when the daemon signals
>>> mount completion.
>>>
>>>>
>>>> Cc: Matthew Wilcox <mawilcox@microsoft.com>
>>>> Cc: Ian Kent <raven@themaw.net>
>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>>> Cc: Stephen Rothwell <sfr@canb.auug.org.au>
>>>> Signed-off-by: Andrei Vagin <avagin@openvz.org>
>>>> ---
>>>>  fs/autofs4/waitq.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
>>>> index c160e9b3aa0f..be9c3dc048ab 100644
>>>> --- a/fs/autofs4/waitq.c
>>>> +++ b/fs/autofs4/waitq.c
>>>> @@ -549,7 +549,7 @@ int autofs4_wait_release(struct autofs_sb_info *sbi, autofs_wqt_t wait_queue_tok
>>>>  	kfree(wq->name.name);
>>>>  	wq->name.name = NULL;	/* Do not wait on this queue */
>>>>  	wq->status = status;
>>>> -	wake_up_interruptible(&wq->queue);
>>>> +	wake_up(&wq->queue);
>>>>  	if (!--wq->wait_ctr)
>>>>  		kfree(wq);
>>>>  	mutex_unlock(&sbi->wq_mutex);
>>>>
>>>
>>