linux-kernel - Re: [PATCH] coredump debugging: add a tracepoint to report the coredumping

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Date: Sun, 18 Feb 2024 23:16:27 +0800
From: Wen Yang <wenyang.linux@...mail.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
 Masami Hiramatsu <mhiramat@...nel.org>, Ingo Molnar <mingo@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Mel Gorman <mgorman@...hsingularity.net>,
 Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coredump debugging: add a tracepoint to report the
 coredumping


On 2024/2/17 18:49, Oleg Nesterov wrote:
> On 02/17, wenyang.linux@...mail.com wrote:
>> From: Wen Yang <wenyang.linux@...mail.com>
>>
>> Currently coredump_task_exit() takes some time to wait for the generation
>> of the dump file. But if the user-space wants to receive a notification
>> as soon as possible it maybe inconvenient.
>>
>> Add the new trace_sched_process_coredump() into coredump_task_exit(),
>> this way a user-space monitor could easily wait for the exits and
>> potentially make some preparations in advance.
> Can't comment, I never know when the new tracepoint will make sense.
>
> Stupid question.
> Oleg.

Thanks for your help.

trace_sched_process_exit() is located after the PF_EXITING flag is set,
so it could not be moved to there.
Could we make the following modifications?

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index dbb01b4b7451..53e9420540dc 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -334,6 +334,13 @@ DEFINE_EVENT(sched_process_template, 
sched_process_exit,
              TP_PROTO(struct task_struct *p),
              TP_ARGS(p));

+/*
+ * Tracepoint for killing a task by a signal:
+ */
+DEFINE_EVENT(sched_process_template, sched_process_kill,
+            TP_PROTO(struct task_struct *p),
+            TP_ARGS(p));
+
  /*
   * Tracepoint for waiting on task to unschedule:
   */
diff --git a/kernel/signal.c b/kernel/signal.c
index 9b40109f0c56..571342799824 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2866,6 +2866,7 @@ bool get_signal(struct ksignal *ksig)
                  * Anything else is fatal, maybe with a core dump.
                  */
                 current->flags |= PF_SIGNALED;
+               trace_sched_process_kill(current);

                 if (sig_kernel_coredump(signr)) {
                         if (print_fatal_signals)

--

Best wishes,

Wen


>
>> Signed-off-by: Wen Yang <wenyang.linux@...mail.com>
>> Cc: Oleg Nesterov <oleg@...hat.com>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Cc: Masami Hiramatsu <mhiramat@...nel.org>
>> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Cc: Mel Gorman <mgorman@...hsingularity.net>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: linux-kernel@...r.kernel.org
>> ---
>>   include/trace/events/sched.h | 7 +++++++
>>   kernel/exit.c                | 1 +
>>   2 files changed, 8 insertions(+)
>>
>> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
>> index dbb01b4b7451..ce7448065986 100644
>> --- a/include/trace/events/sched.h
>> +++ b/include/trace/events/sched.h
>> @@ -334,6 +334,13 @@ DEFINE_EVENT(sched_process_template, sched_process_exit,
>>   	     TP_PROTO(struct task_struct *p),
>>   	     TP_ARGS(p));
>>
>> +/*
>> + * Tracepoint for a task coredumping:
>> + */
>> +DEFINE_EVENT(sched_process_template, sched_process_coredump,
>> +	     TP_PROTO(struct task_struct *p),
>> +	     TP_ARGS(p));
>> +
>>   /*
>>    * Tracepoint for waiting on task to unschedule:
>>    */
>> diff --git a/kernel/exit.c b/kernel/exit.c
>> index 493647fd7c07..c11e12d73f4e 100644
>> --- a/kernel/exit.c
>> +++ b/kernel/exit.c
>> @@ -425,6 +425,7 @@ static void coredump_task_exit(struct task_struct *tsk)
>>   			self.next = xchg(&core_state->dumper.next, &self);
>>   		else
>>   			self.task = NULL;
>> +		trace_sched_process_coredump(tsk);
>>   		/*
>>   		 * Implies mb(), the result of xchg() must be visible
>>   		 * to core_state->dumper.
>> --
>> 2.25.1
>>