Re: [PATCH] printk: Monitor change of console loglevel.

[Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>]

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...

  https://lkml.kernel.org/r/CACT4Y+ay7nuT-7y2JARozV1s0VisuLdN6VT+w9OsEDs1PeBRoA@mail.gmail.com



On 2019/05/25 2:55, Linus Torvalds wrote:
> On Fri, May 24, 2019 at 10:41 AM Joe Perches <joe@perches.com> 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...