linux-kernel - [RFC PATCH 0/3] Fix quiet console in pre-panic scenarios

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Message-Id: <20200315170903.17393-1-erosca@de.adit-jv.com>
Date:   Sun, 15 Mar 2020 18:09:00 +0100
From:   Eugeniu Rosca <roscaeugeniu@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Valdis Kletnieks <valdis.kletnieks@...edu>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andrew Gabbasov <andrew_gabbasov@...tor.com>,
        Dirk Behme <dirk.behme@...bosch.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>
Subject: [RFC PATCH 0/3] Fix quiet console in pre-panic scenarios

Dear community,

The motivation behind this seris is to save days/weeks, if not months,
of debugging efforts for users who:

 * experience an issue like softlockup/hardlockup/hung task/oom, whose
   reproduction is not clear and whose occurrence rate is very low
 * are constrained to use a low loglevel value (1,2,3) in production
 * mostly rely on console logs to debug the issue post-mortem
   (e.g. saved to persistent storage via e.g. pstore)

As pointed out in the last patch from this series, under the above
circumstances, users might simply lack any relevant logs during
post-mortem analysis.

Why this series is marked as RFC is because:
 * There are several possible approaches to turn console verbosity on
   and off. Current series employs the 'ignore_loglevel' functionality,
   but an alternative way is to use the 'console_loglevel' variable. The
   latter is more intrusive, hence the former has been chosen as v1.
 * Manipulating 'ignore_loglevel' might be seen as an abuse, especially
   because it breaks the expectation of users who assume the system to
   be dead silent after passing loglevel=0 on kernel command line.

Thank you for your comments!

Eugeniu Rosca (3):
  printk: convert ignore_loglevel to atomic_t
  printk: add console_verbose_{start,end}
  watchdog: Turn console verbosity on when reporting softlockup

 include/linux/printk.h | 10 ++++++++++
 kernel/printk/printk.c | 30 ++++++++++++++++++++++++++----
 kernel/watchdog.c      |  4 ++++
 3 files changed, 40 insertions(+), 4 deletions(-)

-- 
2.25.0