Date: Wed, 31 May 2006 08:58:33 -0600 From: Scott Long <scottl@samsco.org> To: John Baldwin <jhb@freebsd.org> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, Warner Losh <imp@freebsd.org>, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/dev/syscons/apm apm_saver.c src/sys/i386/bios apm.c apm.h Message-ID: <447DAF19.3050901@samsco.org> In-Reply-To: <200605311050.12156.jhb@freebsd.org> References: <200605252306.k4PN6cCS081708@repoman.freebsd.org> <44766F75.9060100@samsco.org> <200605311050.12156.jhb@freebsd.org>
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John Baldwin wrote:
> On Thursday 25 May 2006 23:01, Scott Long wrote:
>
>>Warner Losh wrote:
>>
>>
>>>imp 2006-05-25 23:06:38 UTC
>>>
>>> FreeBSD src repository
>>>
>>> Modified files:
>>> sys/dev/syscons/apm apm_saver.c
>>> sys/i386/bios apm.c apm.h
>>> Log:
>>> APM was calling the suspend process from a timeout. This meant that
>>> other timeouts could not happen while suspending, including timeouts
>>> for things like msleep. This caused the system to hang on suspend
>>> when the cbb was enabled, since its suspend path powered down the
>>> socket which used a timeout to wait for it to be done.
>>>
>>> APM now creates a thread when it is enabled, and deletes the thread
>>> when it is disabled. This thread takes the place of the timeout by
>>> doing its polling every ~.9s. When the thread is disabled, it will
>>> wakeup early, otherwise it times out and polls the varius things the
>>> old timeout polled (APM events, suspend delays, etc).
>>>
>>> This makes my Sony VAIO 505TS suspend/resume correctly when APM is
>>> enabled (ACPI is black listed on my 505TS).
>>>
>>> This will likely fix other problems with the suspend path where
>>> drivers would sleep with msleep and/or do other timeouts. Maybe
>>> there's some special case code that would use DELAY while suspending
>>> and msleep otherwise that can be revisited and removed.
>>>
>>> This was also tested by glebius@, who pointed out that in the patch I
>>> sent him, I'd forgotten apm_saver.c
>>>
>>> MFC After: 3 weeks
>>
>>In the past, I've been against mandating that callouts/timeouts/generic
>>taskqueues should not be allowed to sleep. However, after looking over
>>the history of this problem as well as others, it seems that it's just
>>too easy for driver authors to make bad assumptions and wind up with a
>>priority inversion/deadlock like this. It would be relatively trivial
>>to mark these contexts as being non-sleepable and have the msleep code
>>enforce it, like is done with ithreads. What do you think? Anyways,
>>thanks for looking at this and fixing it.
>
>
> We already do for timeouts if INVARIANTS is on:
>
> softclock()
> {
> ...
> THREAD_NO_SLEEPING();
> c_func(c_arg);
> THREAD_SLEEPING_OK();
> ...
> }
>
> That has been in place since 6.0 IIRC.
>
I thought that it was only enabled for DIAGNOSTIC.
Scott
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