linux-kernel - Re: [PATCH 0/7] powerpc: Modernize unhandled signals message

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Date:   Thu, 26 Jul 2018 12:20:52 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Murilo Opsfelder Araujo <muriloo@...ux.ibm.com>,
        Michael Neuling <mikey@...ling.org>
Cc:     linux-kernel@...r.kernel.org,
        Alastair D'Silva <alastair@...ilva.org>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@....fr>,
        Cyril Bur <cyrilbur@...il.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Paul Mackerras <paulus@...ba.org>,
        Simon Guo <wei.guo.simon@...il.com>,
        Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        "Tobin C . Harding" <me@...in.cc>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 0/7] powerpc: Modernize unhandled signals message

Murilo Opsfelder Araujo <muriloo@...ux.ibm.com> writes:
> On Wed, Jul 25, 2018 at 05:00:21PM +1000, Michael Neuling wrote:
>>  On Tue, 2018-07-24 at 16:27 -0300, Murilo Opsfelder Araujo wrote:
>> > This series was inspired by the need to modernize and display more
>> > informative messages about unhandled signals.
...
>> 
>> Nice.. the instruction dump would have been very handy when debugging the PCR
>> init issue I had a month or so back.

These things may be related :)

>> What happens if we get a sudden flood of these from different processes that
>> overlap their output? Are we going to be able to match up the process with
>> instruction dump?
>
> As to the flood of messages, ___ratelimit() makes me think that we'll
> likely see some warn messages informing how many show_signal_msg()
> callbacks were suppressed, instead of interleaved messages and
> instruction dumps.
>
> As to matching process with instruction dump, I believe we'd need more
> information to glue them together.
>
> What if we modify show_instructions() to accept a string prefix to be
> printed along with each line?
>
>> Should we prefix every line with the PID to avoid this?
>
> That's possible.  An alternative would be prefixing each line with the
> process name and its PID, as in the first line.  For example:
>
>     pandafault[10758]: segfault (11) at 00000000100007d0 nip 000000001000061c lr 00007fffabc85100 code 2 in pandafault[10000000+10000]
>     pandafault[10758]: Instruction dump:
>     pandafault[10758]: 4bfffeec 4bfffee8 3c401002 38427f00 fbe1fff8 f821ffc1 7c3f0b78 3d22fffe
>     pandafault[10758]: 392988d0 f93f0020 e93f0020 39400048 <99490000> 39200000 7d234b78 383f0040
>
> The above can be interleaved with other messages and we'll still be able
> to match process and its corresponding instruction dump.

Yeah prefixing with the comm and pid is nice.

Also the "Instruction dump:" line is a waste of space.

I prefer the x86 format, where it's prefixed with "code:", eg:

  pandafault[10758]: segfault (11) at 00000000100007d0 nip 000000001000061c lr 00007fffabc85100 code 2 in pandafault[10000000+10000]
  pandafault[10758]: code: 4bfffeec 4bfffee8 3c401002 38427f00 fbe1fff8 f821ffc1 7c3f0b78 3d22fffe
  pandafault[10758]: code: 392988d0 f93f0020 e93f0020 39400048 <99490000> 39200000 7d234b78 383f0040

cheers