linux-kernel - Re: possible trace_printk() bug in v5.19-rc1

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Date:   Fri, 24 Jun 2022 18:23:36 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: possible trace_printk() bug in v5.19-rc1



> On Jun 19, 2022, at 8:57 PM, Chuck Lever III <chuck.lever@...cle.com> wrote:
> 
> Hi Steve-
> 
>> On Jun 17, 2022, at 9:28 PM, Chuck Lever III <chuck.lever@...cle.com> wrote:
>> 
>> 
>> 
>>> On Jun 17, 2022, at 3:50 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
>>> 
>>> On Thu, 16 Jun 2022 15:36:43 +0000
>>> Chuck Lever III <chuck.lever@...cle.com> wrote:
>>> 
>>>>> Did you remove any modules before displaying the trace? 
>>>> 
>>>> I haven't explicitly removed nfsd.ko, and lsmod says it's still there.
>>>> And, trace_printk was working as expected on v5.18.
>>> 
>>> Are you sure?
>> 
>> Yes, I'm sure. I just checked out v5.18 and built it with the
>> same CONFIG. trace_printk() on that kernel generates function
>> names as expected.
> 
> I moved my development work to another system, and bisected. The
> result:
> 
> 91fb02f31505 ("module: Move kallsyms support into a separate file")

The function_graph plug-in is kinda whack-ola too (v5.19-rc3):

   kworker/u25:2-1372  [000]  3465.543709: funcgraph_entry:                   |  ffffffffc0e8c390() {
   kworker/u25:2-1372  [000]  3465.543712: funcgraph_entry:                   |    ktime_get_coarse_with_offset() {
   kworker/u25:2-1372  [000]  3465.543714: funcgraph_entry:                   |      rcu_read_lock_sched_held() {
   kworker/u25:2-1372  [000]  3465.543716: funcgraph_entry:        1.615 us   |        rcu_lockdep_current_cpu_online();
   kworker/u25:2-1372  [000]  3465.543719: funcgraph_exit:         4.857 us   |      }
   kworker/u25:2-1372  [000]  3465.543721: funcgraph_entry:                   |      rcu_read_lock_sched_held() {
   kworker/u25:2-1372  [000]  3465.543722: funcgraph_entry:        1.263 us   |        rcu_lockdep_current_cpu_online();
   kworker/u25:2-1372  [000]  3465.543725: funcgraph_exit:         3.882 us   |      }
   kworker/u25:2-1372  [000]  3465.543726: funcgraph_exit:       + 14.095 us  |    }


--
Chuck Lever