Messages in this thread | | | Subject | Re: [PATCH] x86: Call fixup_exception() before notify_die() in math_error() | From | Andy Lutomirski <> | Date | Tue, 19 Jun 2018 08:23:03 -0700 |
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> On Jun 18, 2018, at 11:23 PM, Thomas Gleixner <tglx@linutronix.de> wrote: > >> On Mon, 18 Jun 2018, Andy Lutomirski wrote: >> >> On Thu, Jun 14, 2018 at 10:10 PM Siarhei Liakh >> <Siarhei.Liakh@concurrent-rt.com> wrote: >>> >>> fpu__drop() has an explicit fwait which under some conditions can trigger >>> a fixable FPU exception while in kernel. Thus, we should attempt to fixup >>> the exception first, and only call notify_die() if the fixup failed just >>> like in do_general_protection(). The original call sequence incorrectly >>> triggers KDB entry on debug kernels under particular FPU-intensive >>> workloads. This issue had been privately observed, fixed, and tested >>> on 4.9.98, while this patch brings the fix to the upstream. >> >> Reviewed-by: Andy Lutomirski <luto@kernel.org> >> >> With the caveat that you are perpetuating what is arguably a bug in >> some of the other entries: math_error() can now be called with IRQs >> off and return with IRQs on. If we actually start asserting good >> behavior in the entry code, we'll need to fix this. > > Confused. math_error() is still invoked with interrupts off. What's > different now is that notify_die() is called with interrupts conditionally > enabled while upstream it's always called with interrupts disabled.
True, but I don’t think that matters. What I’m grumbling about is that we can do cond_local_irq_enable() and then return without local_irq_disable().
Anyway, I think the patch is fine as is. We can unsuck the entry IRQ handling another day.
> > Thanks, > > tglx > > >
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