[PATCH 1/2] exit: add a tracepoint for profiling a task that is starting to exit

[wenyang.linux@foxmail.com]

From: Wen Yang <wenyang.linux@foxmail.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.

Commit 2d4bcf886e42 ("exit: Remove profile_task_exit & profile_munmap")
simplified the code, but also removed profile_task_exit(), which may
prevent third-party kernel modules from detecting process exits timely.

Add the new trace_sched_profile_task_exit() this way a user-space monitor
could detect the exits and potentially make some preparations in advance.

Signed-off-by: Wen Yang <wenyang.linux@foxmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
---
 include/trace/events/sched.h | 28 ++++++++++++++++++++++++++++
 kernel/exit.c                |  1 +
 2 files changed, 29 insertions(+)

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index dbb01b4b7451..750b2f0bdf69 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -341,6 +341,34 @@ DEFINE_EVENT(sched_process_template, sched_wait_task,
 	TP_PROTO(struct task_struct *p),
 	TP_ARGS(p));
 
+/*
+ * Tracepoint for profiling a task that is starting to exit:
+ */
+TRACE_EVENT(sched_profile_task_exit,
+
+	TP_PROTO(struct task_struct *task, long code),
+
+	TP_ARGS(task, code),
+
+	TP_STRUCT__entry(
+		__array(	char,	comm,	TASK_COMM_LEN	)
+		__field(	pid_t,	pid			)
+		__field(	int,	prio			)
+		__field(	long,	code			)
+	),
+
+	TP_fast_assign(
+		memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+		__entry->pid		= task->pid;
+		__entry->prio		= task->prio;
+		__entry->code		= code;
+	),
+
+	TP_printk("comm=%s pid=%d prio=%d exit_code=0x%lx",
+		  __entry->comm, __entry->pid, __entry->prio,
+		  __entry->code)
+);
+
 /*
  * Tracepoint for a waiting task:
  */
diff --git a/kernel/exit.c b/kernel/exit.c
index 493647fd7c07..f675f879a1b2 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -826,6 +826,7 @@ void __noreturn do_exit(long code)
 
 	WARN_ON(tsk->plug);
 
+	trace_sched_profile_task_exit(tsk, code);
 	kcov_task_exit(tsk);
 	kmsan_task_exit(tsk);
 
-- 
2.25.1