From: Michael Ellerman <mpe@ellerman•id.au>
To: Nicholas Piggin <npiggin@gmail•com>
Cc: linuxppc-dev@lists•ozlabs.org,
Benjamin Herrenschmidt <benh@kernel•crashing.org>
Subject: Re: [PATCH 2/4] powerpc/64: do not trace irqs-off at interrupt return to soft-disabled context
Date: Mon, 04 Dec 2017 23:55:55 +1100 [thread overview]
Message-ID: <87fu8qsld0.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <20171204160714.2ff62d11@roar.ozlabs.ibm.com>
Nicholas Piggin <npiggin@gmail•com> writes:
> On Mon, 04 Dec 2017 16:09:57 +1100
> Michael Ellerman <mpe@ellerman•id.au> wrote:
>
>> Nicholas Piggin <npiggin@gmail•com> writes:
>>
>> > When an interrupt is returning to a soft-disabled context (which can
>> > happen for non-maskable interrupts or synchronous interrupts), it goes
>> > through the motions of soft-disabling again, including calling
>> > TRACE_DISABLE_INTS (i.e., trace_hardirqs_off()).
>> >
>> > This is not necessary, because we must already be soft-disabled in the
>> > interrupt context, it also may be causing crashes in the irq tracing
>> > code to re-enter as an nmi. Replace it with a warning to ensure that
>> > soft-interrupts are still disabled.
>> >
>> > Signed-off-by: Nicholas Piggin <npiggin@gmail•com>
>> > ---
>> > arch/powerpc/kernel/entry_64.S | 10 +++++++---
>> > 1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> So this patch is the core of the bug fix I gather.
>>
>> Git blames says:
>>
>> Fixes: 7c0482e3d055 ("powerpc/irq: Fix another case of lazy IRQ state getting out of sync")
>> Cc: stable@vger•kernel.org # v3.4+
>>
>> But I'm wondering how this has been broken that long without us
>> noticing? You hit it doing some sort of perf stress test I think - so is
>> it just that we've never pushed hard enough? Or did something change to
>> expose this? Or we're just not sure?
>
> I'm not really sure. A customer hit it, during either a stress test or
> long running workload with lockdep irq tracing and perf running at the
> same time. I don't have a lot more details but we might be able to get
> some offline if necessary.
No worries.
I'll put it in and add it to my maybe-for-stable list. We can let it
soak a bit and then send it to stable if we think it's necessary and has
no issues.
cheers
next prev parent reply other threads:[~2017-12-04 12:55 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-16 16:00 [PATCH 0/4] interrupt tracing fixes Nicholas Piggin
2017-11-16 16:00 ` [PATCH 1/4] powerpc: define __ARCH_IRQ_EXIT_IRQS_DISABLED Nicholas Piggin
2018-01-22 3:34 ` [1/4] " Michael Ellerman
2017-11-16 16:00 ` [PATCH 2/4] powerpc/64: do not trace irqs-off at interrupt return to soft-disabled context Nicholas Piggin
2017-12-04 5:09 ` Michael Ellerman
2017-12-04 6:07 ` Nicholas Piggin
2017-12-04 12:55 ` Michael Ellerman [this message]
2017-12-04 16:12 ` Benjamin Herrenschmidt
2017-12-05 5:52 ` Michael Ellerman
2017-12-12 11:39 ` [2/4] " Michael Ellerman
2017-11-16 16:00 ` [PATCH 3/4] cpuidle/powernv: avoid double irq enable coming out of idle Nicholas Piggin
2018-01-22 3:34 ` [3/4] " Michael Ellerman
2017-11-16 16:00 ` [PATCH 4/4] " Nicholas Piggin
2018-01-22 3:34 ` [4/4] " Michael Ellerman
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