[PATCH v3] exit: move trace_sched_process_exit earlier in do_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.

Move trace_sched_process_exit() earlier in do_exit().
This way a user-space monitor could detect the exits and
potentially make some preparations in advance.

Oleg initially proposed this suggestion, and Steven further provided some
detailed suggestions, and Mathieu carefully checked the historical code
and said:
: I've checked with Matthew Khouzam (maintainer of Trace Compass)
: which care about this tracepoint, and we have not identified any
: significant impact of moving it on its model of the scheduler, other
: than slightly changing its timing.
: I've also checked quickly in lttng-analyses and have not found
: any code that care about its specific placement.
: So I would say go ahead and move it earlier in do_exit(), it's
: fine by me.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Wen Yang <wenyang.linux@foxmail.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
---
 kernel/exit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 493647fd7c07..2cff6533cb39 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_process_exit(tsk);
 	kcov_task_exit(tsk);
 	kmsan_task_exit(tsk);
 
@@ -866,7 +867,6 @@ void __noreturn do_exit(long code)
 
 	if (group_dead)
 		acct_process();
-	trace_sched_process_exit(tsk);
 
 	exit_sem(tsk);
 	exit_shm(tsk);
-- 
2.25.1