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From: Dmitry Safonov <0x7f454c46@gmail.com>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>,
	Dmitry Safonov <dima@arista.com>
Cc: Juri Lelli <juri.lelli@redhat.com>,
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Subject: Re: [PATCH 00/50] Add log level to show_stack()
Date: Fri, 8 Nov 2019 21:08:30 +0000
Message-ID: <5a411348-be84-f592-ef2d-ffaec99332bd@gmail.com> (raw)
In-Reply-To: <20191108173045.GY25745@shell.armlinux.org.uk>


On 11/8/19 5:30 PM, Russell King - ARM Linux admin wrote:
> On Fri, Nov 08, 2019 at 04:28:30PM +0000, Dmitry Safonov wrote:
[..]
>>
>> Well, the use-case for lower log-level is that everything goes into logs
>> (/var/log/dmesg or /var/log/messages whatever rsyslog has settting).
>>
>> That has it's value:
>> - after a failure (i.e. panic) messages, those were only signs that
>> something goes wrong can be seen in logs which can give ideas what has
>> happened.
> 
> No they don't.  When the kernel panics, userspace generally stops
> running, so rsyslog won't be able to write them to /var/log/messages.
> 
> How, by "kernel panics" I mean a real kernel panic, which probably
> isn't what you're talking about there.  You are probably talking
> about the whole shebang of non-fatal kernel oops, kernel warnings
> and the like.  If so, I'd ask you to stop confuzzilating terminology.
> 
> If you really want to capture such events, then you need to have the
> kernel write the panic to (e.g.) flash - see the mtdoops driver.

I was talking about things prior the panic: OOMs, MMC write/read
warnings, hung tasks, we also have local patches to produce a warning if
the mutex is being held for too long or a task is starving on CPU time
by hard/soft irqs (I hope I will design something like that for
upstream). I've found those warnings useful to:
(a) have an early message when the things are starting going bad.
(b) analyze contentions or too large scale for a box or faulty hardware
for non-reproducible issues just from logs.

We use kexec to save the dmesg ringbuffer content after the panic.

Thanks,
          Dmitry

  reply index

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-06  3:04 Dmitry Safonov
2019-11-06  3:05 ` [PATCH 26/50] powerpc: Add show_stack_loglvl() Dmitry Safonov
2019-11-06  9:52   ` Michael Ellerman
2019-11-06 16:01     ` Dmitry Safonov
2019-11-06  8:35 ` [PATCH 00/50] Add log level to show_stack() Petr Mladek
2019-11-06 16:12   ` Dmitry Safonov
2019-11-08 10:37   ` Sergey Senozhatsky
2019-11-08 13:04     ` Petr Mladek
2019-11-11  1:23       ` Sergey Senozhatsky
2019-11-11  9:12         ` Petr Mladek
2019-11-12  4:44           ` Sergey Senozhatsky
2019-11-12  4:57             ` Sergey Senozhatsky
2019-11-12  8:35               ` Petr Mladek
2019-11-12 10:12                 ` Sergey Senozhatsky
2019-11-13  1:23                   ` Sergey Senozhatsky
2019-11-13  2:25                     ` Dmitry Safonov
2019-11-13  6:33                       ` Sergey Senozhatsky
2019-11-13  8:47                         ` Petr Mladek
2019-11-13 16:24                           ` Steven Rostedt
2019-11-13 16:40                         ` Dmitry Safonov
2019-11-15  0:50                           ` Sergey Senozhatsky
2019-11-13 15:32             ` Steven Rostedt
2019-11-11 19:47         ` Dmitry Safonov
2019-11-12  2:17           ` Sergey Senozhatsky
2019-11-12  2:40             ` Dmitry Safonov
2019-11-12  4:25               ` Sergey Senozhatsky
2019-11-13  2:41                 ` Dmitry Safonov
2019-11-13  2:51                   ` Sergey Senozhatsky
2019-11-13 15:39             ` Steven Rostedt
2019-11-15  3:36               ` Sergey Senozhatsky
2019-11-06  9:20 ` Peter Zijlstra
2019-11-06 16:27   ` Dmitry Safonov
2019-11-06 20:34     ` Peter Zijlstra
2019-11-06 23:25       ` Russell King - ARM Linux admin
2019-11-13 15:44         ` Steven Rostedt
2019-11-08 16:28       ` Dmitry Safonov
2019-11-08 17:30         ` Russell King - ARM Linux admin
2019-11-08 21:08           ` Dmitry Safonov [this message]
2019-11-13 15:41       ` Steven Rostedt

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