Date: Mon, 18 Jan 2010 15:53:52 +0900 (JST) From: Kohji Okuno <okuno.kohji@jp.panasonic.com> To: attilio@freebsd.org Cc: okuno.kohji@jp.panasonic.com, freebsd-current@freebsd.org, jroberson@jroberson.net Subject: Re: Bug about sched_4bsd? Message-ID: <20100118.155352.59640143160034670.okuno.kohji@jp.panasonic.com> In-Reply-To: <3bbf2fe11001171858o4568fe38l9b2db54ec9856b50@mail.gmail.com> References: <20100117.142200.321689433999177718.okuno.kohji@jp.panasonic.com> <20100117.152835.119882392487126976.okuno.kohji@jp.panasonic.com> <3bbf2fe11001171858o4568fe38l9b2db54ec9856b50@mail.gmail.com>
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Hello,
Thank you, Attilio.
I checked your patch. I think that your patch is better.
I tested the patch quickly, and I think it's OK.
# This probrem does not occur easily :-<
What do you think about maybe_resched()?
I have never experienced about maybe_resched(), but I think that the
race condition may occur.
<<Back Trace>>
sched_4bsd.c: maybe_resched()
sched_4bsd.c: resetpriority_thread()
sched_4bsd.c: sched_nice() get thread_lock(td)
kern_resource.c: donice()
kern_resource.c: setpriority() get PROC_LOCK()
static void
maybe_resched(struct thread *td)
{
THREAD_LOCK_ASSERT(td, MA_OWNED);
if (td->td_priority < curthread->td_priority)
curthread->td_flags |= TDF_NEEDRESCHED;
}
I think, when td->td_lock is not &sched_lock, curthread->td_lock is
not locked in maybe_resched().
Best regards,
Kohji Okuno.
From: Attilio Rao <attilio@freebsd.org>
Subject: Re: Bug about sched_4bsd?
Date: Mon, 18 Jan 2010 03:58:41 +0100
Message-ID: <3bbf2fe11001171858o4568fe38l9b2db54ec9856b50@mail.gmail.com>
> 2010/1/17 Kohji Okuno <okuno.kohji@jp.panasonic.com>:
>> Hello,
>>
>> Could you check sched_4bsd.patch, please?
>
> I think, instead, that what needs to happen is to have sched_switch()
> to do a lock handover from sleepq/turnstile spinlock to schedlock.
> That way, if threads are willing to contest on td_lock they will be
> still inhibited.
> I'm not sure if this patch breaks any invariant, if you may test I
> would appreciate:
> http://www.freebsd.org/~attilio/sched_4bsd_schedlock.diff
>
> Reviews and comments are appreciated.
> BTW, nice catch.
>
> Attilio
>
>
> --
> Peace can only be achieved by understanding - A. Einstein
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