linux-kernel - Re: [PATCH] ioapic: fix potential resume deadlock

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Date:	Thu, 12 May 2011 00:15:04 +0800
From:	Daniel J Blueman <daniel.blueman@...il.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ioapic: fix potential resume deadlock

On 11 May 2011 07:58, Suresh Siddha <suresh.b.siddha@...el.com> wrote:
> On Tue, 2011-05-10 at 03:53 -0700, Daniel J Blueman wrote:
>> On 10 May 2011 15:35, Ingo Molnar <mingo@...e.hu> wrote:
>> > Hm, there must be some other bug here.
>> >
>> > ioapic entries should be allocated on system bootup and should never really be
>> > deallocated.
>> >
>> > The bug might be in the idea to call to enable_IR_x2apic() on resume - why are
>> > ioapic entries reallocated there? That call in default_setup_apic_routing() was
>> > introduced some time ago in:
>> >
>> >  fa47f7e52874: x86, x2apic: Simplify apic init in SMP and UP builds
>> >
>> > and that it results in reallocation in the suspend patch is distinctly wrong.
>> >
>> > I suspect the reason why this has not triggered for others is the relative
>> > rarity of affected systems?
>> >
>> > Suresh?
>
> This will happen only on interrupt-remapping enabled systems and hence
> hidden so far.
>
> enable_IR_x2apic() / default_setup_apic_routing() routines don't get
> called during resume. Problem is with the lapic_resume() path which is
> trying to re-enable x2apic mode and this requires masking io-apic
> entries, re-enabling x2apic and interrupt-remapping, restoring io-apic
> entries etc. ioapic entry allocation that is happening in lapic_resume()
> is just for storing the original io-apic RTE's during the mask/restore
> operations that happen around re-enabling x2apic.
>
> Anyways looking at that code, there is some duplicate code between
> x2apic code and the io-apic suspend/resume sequence. So a better fix
> will be to remove this duplicate code.
>
> Daniel, I appended a quick patch which should fix the problem you
> reported. This is not a final patch, as I can do some more cleanup and
> re-use the io-apic suspend/resume code a bit more.
>
> If this patch works for you, then I can spend some more time to do the
> complete cleanup patch in a day or two. Thanks.
[...]

Superb, this works, tested against 2.6.39-rc7 and addresses the "BUG:
sleeping function called from invalid context at mm/slub.c:824"
warning I was previously seeing. It would be good to get this fix into
2.6.39-final if possible.

Tested-by: Daniel J Blueman <daniel.blueman@...il.com>

Thanks,
  Daniel
-- 
Daniel J Blueman
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