From: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
To: Borislav Petkov <bp@alien8.de>, pmladek@suse.com
Cc: linux-edac@vger.kernel.org, kexec@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org,
netdev@vger.kernel.org, x86@kernel.org, kernel-dev@igalia.com,
kernel@gpiccoli.net, Dinh Nguyen <dinguyen@kernel.org>,
Rabara Niravkumar L <niravkumar.l.rabara@intel.com>,
Tony Luck <tony.luck@intel.com>
Subject: Re: [PATCH V3 08/11] EDAC/altera: Skip the panic notifier if kdump is loaded
Date: Fri, 10 Feb 2023 13:01:32 -0300 [thread overview]
Message-ID: <9efcde8e-c87e-43ff-4d66-5f448d111940@igalia.com> (raw)
In-Reply-To: <Y3zlghMzlc1kzVJx@zn.tnic>
Hi Boris and Petr, first of all thanks for your great analysis and
really sorry for the huge delay in my response.
Below I'm pasting the 2 relevant responses from both Petr and Boris.
On 22/11/2022 12:06, Borislav Petkov wrote:
> On Tue, Nov 22, 2022 at 10:33:12AM -0300, Guilherme G. Piccoli wrote:
>
> Leaving in the whole thing for newly added people.
>
>> On 18/09/2022 11:10, Guilherme G. Piccoli wrote:
>>> On 19/08/2022 19:17, Guilherme G. Piccoli wrote:
>>>> The altera_edac panic notifier performs some data collection with
>>>> regards errors detected; such code relies in the regmap layer to
>>>> perform reads/writes, so the code is abstracted and there is some
>>>> risk level to execute that, since the panic path runs in atomic
>>>> context, with interrupts/preemption and secondary CPUs disabled.
>>>>
>>>> Users want the information collected in this panic notifier though,
>>>> so in order to balance the risk/benefit, let's skip the altera panic
>>>> notifier if kdump is loaded. While at it, remove a useless header
>>>> and encompass a macro inside the sole ifdef block it is used.
>>>>
>>>> Cc: Borislav Petkov <bp@alien8.de>
>>>> Cc: Petr Mladek <pmladek@suse.com>
>>>> Cc: Tony Luck <tony.luck@intel.com>
>>>> Acked-by: Dinh Nguyen <dinguyen@kernel.org>
>>>> Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
>>>>
>>>> ---
>>>>
>>>> V3:
>>>> - added the ack tag from Dinh - thanks!
>>>> - had a good discussion with Boris about that in V2 [0],
>>>> hopefully we can continue and reach a consensus in this V3.
>>>> [0] https://lore.kernel.org/lkml/46137c67-25b4-6657-33b7-cffdc7afc0d7@igalia.com/
>>>>
>>>> V2:
>>>> - new patch, based on the discussion in [1].
>>>> [1] https://lore.kernel.org/lkml/62a63fc2-346f-f375-043a-fa21385279df@igalia.com/
>>>>
>>>> [...]
>>>
>>> Hi Dinh, Tony, Boris - sorry for the ping.
>>>
>>> Appreciate reviews on this one - Dinh already ACKed the patch but Boris
>>> raised some points in the past version [0], so any opinions or
>>> discussions are welcome!
>>
>>
>> Hi folks, monthly ping heheh
>> Apologies for the re-pings, please let me know if there is anything
>> required to move on this patch.
>
> Looking at this again, I really don't like the sprinkling of
>
> if (kexec_crash_loaded())
>
> in unrelated code. And I still think that the real fix here is to kill
> this
>
> edac->panic_notifier
>
> thing. And replace it with simply logging the error from the double bit
> error interrupt handle. That DBERR IRQ thing altr_edac_a10_irq_handler().
> Because this is what this panic notifier does - dump double-bit errors.
>
> Now, if Dinh doesn't move, I guess we can ask Tony and/or Rabara (he has
> sent a patch for this driver recently and Altera belongs to Intel now)
> to find someone who can test such a change and we (you could give it a
> try first :)) can do that change.
>
> Thx.
>
On 09/12/2022 13:03, Petr Mladek wrote:> [...]>
> I have read the discussion about v2 [1] and this looks like a bad
> approach from my POV.
>
> My understanding is that the information provided by this notifier
> could not be found in the crashdump. It means that people really
> want to run this before crashdump in principle.
>
> Of course, there is the question how much safe this code is. I mean
> if the panic() code path might get blocked here.
>
> I see two possibilities.
>
> The best solution would be if we know that this is "always" safe or if
> it can be done a safe way. Then we could keep it as it is or implement
> the safe way.
>
> Alternative solution would be to create a kernel parameter that
> would enable/disable this particular report when kdump is enabled.
> The question would be the default. It would depend on how risky
> the code is and how useful the information is.
>
> [1] https://lore.kernel.org/r/20220719195325.402745-11-gpiccoli@igalia.com
>
So, for me Petr approach is the more straightforward, though we could
rethink the idea of this notifier being...a notifier, as suggest Boris heh
Anyway, what I plan to do is: I'll re-submit a simple clean-up for this
code (header / ifdef stuff), not functional-changing the code path.
After that, when re-submitting the V2 or the notifiers refactor (which
I'm pending for some good months =O ), I'll deal with this code
properly, factoring the ideas and proposing a meaningful change.
So, let's discard this patch for now.
Thanks again,
Guilherme
next prev parent reply other threads:[~2023-02-10 16:01 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-19 22:17 [PATCH V3 00/11] The panic notifiers refactor - fixes/clean-ups (V3) Guilherme G. Piccoli
2022-08-19 22:17 ` [PATCH V3 01/11] ARM: Disable FIQs (but not IRQs) on CPUs shutdown paths Guilherme G. Piccoli
2022-09-18 13:58 ` Guilherme G. Piccoli
2022-10-17 14:00 ` Guilherme G. Piccoli
2022-10-17 14:17 ` Russell King (Oracle)
2022-10-17 14:50 ` Guilherme G. Piccoli
2022-10-17 17:47 ` Russell King (Oracle)
2022-10-17 19:43 ` Guilherme G. Piccoli
2022-08-19 22:17 ` [PATCH V3 02/11] notifier: Add panic notifiers info and purge trailing whitespaces Guilherme G. Piccoli
2022-11-22 13:19 ` Guilherme G. Piccoli
2022-08-19 22:17 ` [PATCH V3 03/11] alpha: Clean-up the panic notifier code Guilherme G. Piccoli
2022-11-22 13:22 ` Guilherme G. Piccoli
2022-08-19 22:17 ` [PATCH V3 04/11] um: Improve panic notifiers consistency and ordering Guilherme G. Piccoli
2022-09-18 14:00 ` Guilherme G. Piccoli
2022-09-18 21:19 ` Richard Weinberger
2022-09-19 11:44 ` Guilherme G. Piccoli
2022-10-17 14:01 ` Guilherme G. Piccoli
2022-10-17 14:10 ` Richard Weinberger
2022-10-17 14:22 ` Guilherme G. Piccoli
2022-08-19 22:17 ` [PATCH V3 05/11] parisc: Replace regular spinlock with spin_trylock on panic path Guilherme G. Piccoli
2022-08-19 22:17 ` [PATCH V3 06/11] tracing: Improve panic/die notifiers Guilherme G. Piccoli
2022-09-18 14:04 ` Guilherme G. Piccoli
2022-10-17 14:02 ` Guilherme G. Piccoli
2022-10-20 21:29 ` Steven Rostedt
2022-10-20 21:53 ` Guilherme G. Piccoli
2022-10-20 22:22 ` Steven Rostedt
2022-10-20 22:37 ` Guilherme G. Piccoli
2022-11-22 13:27 ` Guilherme G. Piccoli
2022-12-13 23:51 ` Guilherme G. Piccoli
2022-12-14 0:06 ` Steven Rostedt
2022-12-14 0:52 ` Guilherme G. Piccoli
2022-08-19 22:17 ` [PATCH V3 07/11] notifiers: Add tracepoints to the notifiers infrastructure Guilherme G. Piccoli
2022-09-18 14:07 ` Guilherme G. Piccoli
2022-10-17 14:04 ` Guilherme G. Piccoli
2022-11-22 13:30 ` Guilherme G. Piccoli
2022-08-19 22:17 ` [PATCH V3 08/11] EDAC/altera: Skip the panic notifier if kdump is loaded Guilherme G. Piccoli
2022-09-18 14:10 ` Guilherme G. Piccoli
2022-10-17 14:05 ` Guilherme G. Piccoli
2022-11-22 13:33 ` Guilherme G. Piccoli
2022-11-22 15:06 ` Borislav Petkov
2023-02-10 16:01 ` Guilherme G. Piccoli [this message]
2022-12-09 16:03 ` Petr Mladek
2022-08-19 22:17 ` [PATCH V3 09/11] video/hyperv_fb: Avoid taking busy spinlock on panic path Guilherme G. Piccoli
2022-09-18 14:12 ` Guilherme G. Piccoli
2022-10-04 16:17 ` Michael Kelley (LINUX)
2022-08-19 22:17 ` [PATCH V3 10/11] drivers/hv/vmbus, video/hyperv_fb: Untangle and refactor Hyper-V panic notifiers Guilherme G. Piccoli
2022-10-04 16:24 ` Michael Kelley (LINUX)
2022-10-04 17:20 ` Guilherme G. Piccoli
2022-10-17 15:26 ` Michael Kelley (LINUX)
2022-11-10 21:32 ` Guilherme G. Piccoli
2022-11-11 22:47 ` Wei Liu
2022-11-11 23:16 ` Wei Liu
2022-11-12 21:53 ` Guilherme G. Piccoli
2022-08-19 22:17 ` [PATCH V3 11/11] panic: Fixes the panic_print NMI backtrace setting Guilherme G. Piccoli
2022-09-18 14:13 ` Guilherme G. Piccoli
2022-11-22 13:35 ` Guilherme G. Piccoli
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