svn commit: r286880 - head/sys/kern

[Julien Charbon]

 Hi Konstantin,

On 27/08/15 19:19, Konstantin Belousov wrote:
> On Thu, Aug 27, 2015 at 06:28:03PM +0200, Julien Charbon wrote:
>> On 27/08/15 12:49, Konstantin Belousov wrote:
>>> On Wed, Aug 26, 2015 at 08:14:15PM +0200, Julien Charbon wrote:
>>>>  As I said, I am not opposed to back out this change, callout(9) API in
>>>> mpsafe mode is a already complex/subtle API, it won't change too much
>>>> the current complexity.
>>>>
>>>>  Let say that if nobody screams until Friday 8/28, I will put back
>>>> r284245 and revert this change _and_ I will make this case clear in the
>>>> man page.
>>>
>>> [Replying to a random message in the whole set of conversations]
>>>
>>> There is one more case, besides TCP timers, which is equially, of not
>>> more, critical and sensitive WRT to the callout_stop().  Look at the
>>> sys/kern/subr_sleepqueue.c:sleepq_check_timeout().  Stray return of
>>> the false result from callout_stop() causes creation of the non-killable
>>> processes:  the callout fired, we missed the wakeup and went to sleep
>>> by manually doing the context switch.  Such thread cannot be woken up.
>>>
>>> I suspect that your fix is a better approach than my attempt to look
>>> at something similar at PR 200992 (may be not).
>>
>>  This change (r286880) won't improve the PR 200992:
>>
>>  r286880 only addresses a case where callout_stop() returns 1 instead of
>> 0.  Thus the only thing that can do r286880 to PR 200992:
>>
>>  - Don't change anything the issues
>>  - Worsen the issue
>>
>>  Sorry to kill your hope of a simple and elegant fix for PR 200992.
> 
> Well, not that I am frustrated much.  Thank you for taking a look.
> Did you read the patch attached to the PR ?

 Right, I read it from here:

https://bugs.freebsd.org/bugzilla/attachment.cgi?id=157915&action=diff

 And I am not confident enough to say if it is the right way go.  I
became knowledgeable on callout calls from TCP timers (D2079 and D2763),
but that's it.

 I would propose rrs (as he introduced the 'not_on_a_list' logic) and
jhb for reviewing your patch.

 And unlike me (D3078), don't underestimate the callout complexity in
mpsafe mode. :)

--
Julien

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