From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
X86 ML <x86@kernel.org>
Subject: Re: WARNING: CPU: 0 PID: 3031 at ./arch/x86/include/asm/fpu/internal.h:530 fpu__restore+0x90/0x130()
Date: Wed, 17 Feb 2016 10:35:12 +0100 [thread overview]
Message-ID: <20160217093511.GC19001@gmail.com> (raw)
In-Reply-To: <20160217092911.GA2023@pd.tnic>
* Borislav Petkov <bp@alien8.de> wrote:
> On Wed, Feb 17, 2016 at 09:16:46AM +0100, Ingo Molnar wrote:
> > So I'm wondering why this started triggering only now. Is this a pre-existing bug
> > that somehow got triggered via:
> >
> > 58122bf1d856 x86/fpu: Default eagerfpu=on on all CPUs
> >
> > ?
>
> Well, that's an interesting question. See, the thing is, I triggered
> this only *once* by accident and I haven't seen it ever since.
>
> The "reliable" "reproducer" I used to debug this was Andy's suggestion
> to stick a schedule() in __fpu__restore_sig().
>
> So the answer to that question is not easy.
>
> BUT(!), regardless, the bug still needs to be fixed because my tracing
> here
The fix is absolutely needed, I just would like deeper analysis about how it
wasn't seen before.
> > If yes then we need a plausible theory of how that never triggered on modern
> > Intel CPUs that had eagerfpu enabled for years.
>
> AFAICT, it triggers - and the window is very small at that - only on
> 32-bit. If at all.
So it probably triggers on vanilla v4.4 (or v4.5-rc4) as well, with no recent FPU
bits applied?
> I can certainly try to test all those but I don't have a reliable reproducer.
> The only thing I could do is check out each of those commits and stick a
> schedule() in __fpu__restore_sig() and see what happens.
>
> But if my analysis above is right, none of those would matter because of the
> mechanism of how the warn happens...
So if you stick a schedule() into vanilla and it triggers then I think we can
declare it an existing bug. (and then the fix also needs Cc: stable)
Thanks,
Ingo
next prev parent reply other threads:[~2016-02-17 9:35 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-11 19:27 WARNING: CPU: 0 PID: 3031 at ./arch/x86/include/asm/fpu/internal.h:530 fpu__restore+0x90/0x130() Borislav Petkov
2016-02-11 23:47 ` Andy Lutomirski
2016-02-12 1:16 ` Andy Lutomirski
2016-02-12 17:00 ` Borislav Petkov
2016-02-15 19:14 ` Borislav Petkov
2016-02-16 2:25 ` Andy Lutomirski
2016-02-17 8:16 ` Ingo Molnar
2016-02-17 9:29 ` Borislav Petkov
2016-02-17 9:35 ` Ingo Molnar [this message]
2016-02-17 10:31 ` Borislav Petkov
2016-02-17 11:06 ` Ingo Molnar
2016-02-17 11:41 ` Borislav Petkov
2016-02-17 17:52 ` Andy Lutomirski
2016-02-15 19:05 ` Borislav Petkov
2016-02-12 11:17 ` Borislav Petkov
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