On 11/6/19 8:35 AM, Petr Mladek wrote:

On Wed 2019-11-06 03:04:51, Dmitry Safonov wrote:

quoted

Add log level argument to show_stack().
Done in three stages:
1. Introducing show_stack_loglvl() for every architecture
2. Migrating old users with an explicit log level
3. Renaming show_stack_loglvl() into show_stack()

Justification:
o It's a design mistake to move a business-logic decision
  into platform realization detail.
o I have currently two patches sets that would benefit from this work:
  Removing console_loglevel jumps in sysrq driver [1]

Just to clarify. The problem in sysrq driver is a bit different.
It modifies console_loglevel to show even less important message
on the console.

IMHO, it should be solved by printing the header line with pr_error().
It is not ideal. A cleaner solution might be to introduce another
loglevel that will always get pushed to the console. But I am
not sure if it is worth this single line.

I believe why it's not done - there is a comment in sysrq code that said
the userspace relies on the loglevel of sysrq messages (and may trigger
alerts from emerg/err log level):
  * Raise the apparent loglevel to maximum so that the sysrq header
  * is shown to provide the user with positive feedback.  We do not
  * simply emit this at KERN_EMERG as that would change message
  * routing in the consumers of /proc/kmsg.

But I don't mind any solution.

quoted

  Hung task warning before panic [2] - suggested by Tetsuo (but he
  probably didn't realise what it would involve).
o While doing (1), (2) the backtraces were adjusted to headers
  and other messages for each situation - so there won't be a situation
  when the backtrace is printed, but the headers are missing because
  they have lesser log level (or the reverse).
o As the result in (2) plays with console_loglevel for kdb are removed.

quoted

The least important for upstream, but maybe still worth to note that
every company I've worked in so far had an off-list patch to print
backtrace with the needed log level (but only for the architecture they
cared about).
If you have other ideas how you will benefit from show_stack() with
a log level - please, reply to this cover letter.

I agree with all the other justification.

I would add. The backtrace is really useful for debugging. It should
be possible to print it even in less critical situations.

I am afraid that many people use WARN() for this purpose. But WARN()
is not always appropriate. WARN() misuse huts when panic_on_warn
option is used.

Thanks, Petr.

-- 
          Dmitry