[PATCH] rethook: Use tsk->on_cpu to check task execution state

[PATCH] rethook: Use tsk->on_cpu to check task execution state

[Tengda Wu]

When a task calls schedule() to yield the CPU, its state remains
TASK_RUNNING, but its stack is frozen and safe to walk.

Replace task_is_running(tsk) with tsk->on_cpu to avoid overly
conservative rejections.

Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook")
Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
---
 kernel/trace/rethook.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
index 5a8bdf88999a..bd5e5f455e85 100644
--- a/kernel/trace/rethook.c
+++ b/kernel/trace/rethook.c
@@ -250,7 +250,7 @@ unsigned long rethook_find_ret_addr(struct task_struct *tsk, unsigned long frame
 	if (WARN_ON_ONCE(!cur))
 		return 0;
 
-	if (tsk != current && task_is_running(tsk))
+	if (tsk != current && tsk->on_cpu)
 		return 0;
 
 	do {
-- 
2.34.1

Re: [PATCH] rethook: Use tsk->on_cpu to check task execution state

[Masami Hiramatsu]

On Mon, 25 May 2026 21:22:53 +0800
Tengda Wu <wutengda@huaweicloud.com> wrote:

> When a task calls schedule() to yield the CPU, its state remains
> TASK_RUNNING, but its stack is frozen and safe to walk.
> 
> Replace task_is_running(tsk) with tsk->on_cpu to avoid overly
> conservative rejections.

Please see the Sashiko's comment.

https://sashiko.dev/#/patchset/20260525132253.1889726-1-wutengda%40huaweicloud.com

When calling Unwind on a task other than the current, IMHO, it is
the responsibility of the caller of this function to ensure that the
stack trace of that task is safe.
We also should not use tsk->on_cpu, but should use task_on_cpu(tsk).

BTW, should task_on_cpu() use READ_ONCE() etc?
wait_task_inactive() seems a bit fragile.

Thanks,

> 
> Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook")
> Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
> ---
>  kernel/trace/rethook.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> index 5a8bdf88999a..bd5e5f455e85 100644
> --- a/kernel/trace/rethook.c
> +++ b/kernel/trace/rethook.c
> @@ -250,7 +250,7 @@ unsigned long rethook_find_ret_addr(struct task_struct *tsk, unsigned long frame
>  	if (WARN_ON_ONCE(!cur))
>  		return 0;
>  
> -	if (tsk != current && task_is_running(tsk))
> +	if (tsk != current && tsk->on_cpu)
>  		return 0;
>  
>  	do {
> -- 
> 2.34.1
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>