linux-kernel - [PATCH v2] PM / Freezer: Skip dead/zombie processes

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Message-Id: <20250523034253.88083-1-zhangzihuan@kylinos.cn>
Date: Fri, 23 May 2025 11:42:53 +0800
From: Zihuan Zhang <zhangzihuan@...inos.cn>
To: rafael@...nel.org,
	len.brown@...el.com,
	pavel@...nel.org
Cc: linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Zihuan Zhang <zhangzihuan@...inos.cn>
Subject: [PATCH v2] PM / Freezer: Skip dead/zombie processes

ZOMBIE (exit_state == EXIT_ZOMBIE) and DEAD (exit_state == EXIT_DEAD)
processes have already finished execution and will not be scheduled again.

In the context of system suspend (e.g., S3), attempting to freeze such
processes is unnecessary. Moreover, freezing them can obscure suspend
diagnostics and delay resume if they appear "stuck" in logs.

This patch introduces an early check for `p->exit_state != 0` in
`try_to_freeze_tasks()` and skips freezing for such tasks. This is a safe
optimization because:

 - They hold no running resources
 - Their `task_struct` is only waiting to be collected or freed

Signed-off-by: Zihuan Zhang <zhangzihuan@...inos.cn>

Changes in v2:
- Simplified code, added judgment of dead processes
- Rewrite changelogs
---
 kernel/power/process.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/power/process.c b/kernel/power/process.c
index 66ac067d9ae6..82528a79d46a 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -51,7 +51,7 @@ static int try_to_freeze_tasks(bool user_only)
 		todo = 0;
 		read_lock(&tasklist_lock);
 		for_each_process_thread(g, p) {
-			if (p == current || !freeze_task(p))
+			if (p == current || p->exit_state || !freeze_task(p))
 				continue;

 			todo++;
-- 
2.25.1