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Date:   Sat, 25 May 2019 09:14:15 +0900
From:   Tetsuo Handa <>
To:     Linus Torvalds <>
Cc:     Andrew Morton <>,
        Linux List Kernel Mailing <>,
        Dmitry Vyukov <>,
        Petr Mladek <>,
        Sergey Senozhatsky <>,
        Joe Perches <>
Subject: Re: [PATCH] printk: Monitor change of console loglevel.

On 2019/05/25 2:17, Linus Torvalds wrote:
> A config option or two that help syzbot doesn't sound like a bad idea to me.

Thanks for suggestion. I think that #ifdef'ing

  static bool suppress_message_printing(int level)
  	return (level >= console_loglevel && !ignore_loglevel);

is simpler. If the cause of unexpected change of console loglevel
turns out to be syz_execute_func(), we will want a config option
which controls suppress_message_printing() for syzbot. That option
would also be used for guarding printk("WARNING:" ...) users.

Well, syzbot does not want to use ignore_loglevel kernel command
line option because that option would generate too much output...

On 2019/05/25 2:55, Linus Torvalds wrote:
> On Fri, May 24, 2019 at 10:41 AM Joe Perches <> wrote:
> >
> > That could also help eliminate unnecessary pr_<foo> output
> > from object code.
> Indeed. The small-config people might like it (if they haven't already
> given up..)

Do you mean doing e.g.

  #define pr_debug(fmt, ...) no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)

depending on the minimal console loglevel kernel config option? Then, OK.
But callers using e.g. printk(KERN_DEBUG ...) and printk(KERN_SOH "%u" ...)
will remain unfiltered...

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