Re: [PATCH] selftests: livepatch: handle PRINTK_CALLER in check_result()

[Joe Lawrence <joe.lawrence@redhat.com>]

On 1/16/25 04:29, Petr Mladek wrote:
> On Tue 2025-01-14 20:01:44, Madhavan Srinivasan wrote:
>> Some arch configs (like ppc64) enable CONFIG_PRINTK_CALLER, which
>> adds the caller id as part of the dmesg. Due to this, even though
>> the expected vs observed are same, end testcase results are failed.
> 
> CONFIG_PRINTK_CALLER is not the only culprit. We (SUSE) have it enabled
> as well and the selftests pass without this patch.
> 
> The difference might be in dmesg. It shows the caller only when
> the messages are read via the syslog syscall (-S) option. It should
> not show the caller when the messages are read via /dev/kmsg
> which should be the default.
> 
> I wonder if you define an alias to dmesg which adds the "-S" option
> or if /dev/kmsg is not usable from some reason.
> 

Hi Petr,

To see the thread markers on a RHEL-9.6 machine, I built and installed
the latest dmesg from:

  https://github.com/util-linux/util-linux

and ran Madhavan's tests.  I don't think there was any alias involved:

  $ alias | grep dmesg
  (nothing)

  $ ~/util-linux/dmesg | tail -n1
  [ 4361.322790] [  T98877] % rmmod test_klp_livepatch

From util-linux's 467a5b3192f1 ("dmesg: add caller_id support"):

 The dmesg -S using the old syslog interface supports printing the
 PRINTK_CALLER field but currently standard dmesg does not support
 printing the field if present. There are utilities that use dmesg and
 so it would be optimal if dmesg supported PRINTK_CALLER as well.

does that imply that printing the thread IDs is now a (util-linux's)
dmesg default?

Regards,

-- 
Joe