linux-kernel - Re: [PATCH 1/2] panic: ratelimit panic messages

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Message-ID: <AANLkTinWqVHN=1hMmz-wqz2ot=MP8SCQmgjtPMFLmDG3@mail.gmail.com>
Date:	Sat, 15 Jan 2011 16:29:13 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	fweisbec@...il.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] panic: ratelimit panic messages

On Thu, Jan 6, 2011 at 6:51 AM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Tue,  4 Jan 2011 22:38:30 -0500
> Don Zickus <dzickus@...hat.com> wrote:
>
>> Sometimes when things go bad, so much spew is coming on the console it is hard
>> to figure out what happened.  This patch allows you to ratelimit the panic
>> messages with the intent that the first panic message will provide the info
>> we need to figure out what happened.
>>
>> Adds new kernel param 'panic_ratelimit=on/<integer in seconds>'
>>
>
> Terminological whinge: panic() is a specific kernel API which ends up
> doing a sort-of-oops thing.  So the graph is
>
>        panic           -> oops
>        other-things    -> oops
>
> Your patch doesn't affect only panics - it also affects oops, BUG(),
> etc.  So I'd suggest that this patch should do s/panic/oops/g.
>
>> ---
>>  Documentation/kernel-parameters.txt |    6 ++++++
>>  kernel/panic.c                      |   30 ++++++++++++++++++++++++++++++
>>  2 files changed, 36 insertions(+), 0 deletions(-)
>>
>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> index 316c723..1416964 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -1807,6 +1807,12 @@ and is between 256 and 4096 characters. It is defined in the file
>>       panic=          [KNL] Kernel behaviour on panic
>>                       Format: <timeout>
>>
>> +     panic_ratelimit=        [KNL] ratelimit the panic messages
>> +                     Useful for slowing down multiple panics to capture
>> +                     the first one before it scrolls off the screen
>> +                     Format: "on" or some integer in seconds
>> +                     "on" defaults to 10 minutes
>> +
>
> We keep on hacking away at this and things never seem to get much
> better.  It's still the case that a large number of our oops reports
> are damaged because the important parts of the oops trace scrolled off
> the screen.
>
> I therefore propose
>
>        oops_lines_delay=N,M
>
> which will cause the kernel to pause for M milliseconds after emitting
> N lines of oops output.  Bonus marks for handling linewrap!

I ever try to do similar things to printk_delay, something like
printk_lines_delay,
or give printk_delay one more parameter of lines.

What do you think about this approach?

>
> Start the line counter at oops_begin() or thereabouts and then do the
> delay after N lines have been emitted.  I guess that counter should
> _not_ be invalidated in oops_end(): if the oops generates 12 lines and
> then another 100 lines of random printk crap are printed, we still want
> to put a pause after the 13th line of that random crap, so we can view
> the oops.
>
> The oops_lines_delay implemetnation should count lines from all CPUs
> and should block all CPUs during the delay.
>
> I think this would solve the problem which you're seeing, as well as
> the much larger my-oops-scrolled-off problem?
>
> --
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-- 
Regards
dave
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