linux-kernel - [RESEND PATCH v3] exit: move trace_sched_process_exit earlier in do

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <tencent_F5D82FE0B9A0CA9C3A29C866F225FD915905@qq.com>
Date: Sat, 30 Mar 2024 10:52:38 +0800
From: wenyang.linux@...mail.com
To: Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>
Cc: Wen Yang <wenyang.linux@...mail.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Christian Brauner <brauner@...nel.org>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: [RESEND PATCH v3] exit: move trace_sched_process_exit earlier in do_exit()

From: Wen Yang <wenyang.linux@...mail.com>

In a safety critical system, when some processes exit abnormally,
it is hoped that prompt information can be reported to the monitor
as soon as possible.

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.

Compared to adding an extra tracking point, it is better to move the
existing trace_sched_process_exit() earlier in do_exit(), since any tracer
interested in knowing the point where a task is really reclaimed is
trace_sched_process_free() called from delayed_put_task_struct().[1]

Andrew raised a concern:
If userspace is awaiting this notification to say "it's now OK to read
the dump file" then it could break things?
The nearby proc_exit_connector() can be used for this purpose. But we
couldn't find any specific code that concerns the location of
trace_sched_process_exit().

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. [2]

[1]: https://lore.kernel.org/all/c411eda5-5378-4511-bea3-d1566174c8c7@efficios.com/
[2]: https://lore.kernel.org/all/c9427e40-10b1-49eb-9baa-dde1364e8fe5@efficios.com/

Suggested-by: Oleg Nesterov <oleg@...hat.com>
Suggested-by: Steven Rostedt <rostedt@...dmis.org>
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Signed-off-by: Wen Yang <wenyang.linux@...mail.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Christian Brauner <brauner@...nel.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.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