linux-kernel - Re: [PATCH] stacktrace: do not trace user stack for user

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Message-ID: <20250624130744.602c5b5f@batman.local.home>
Date: Tue, 24 Jun 2025 13:07:44 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Jiazi Li <jqqlijiazi@...il.com>
Cc: linux-kernel@...r.kernel.org, "peixuan.qiu" <peixuan.qiu@...nssion.com>,
 Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org
Subject: Re: [PATCH] stacktrace: do not trace user stack for user_worker
 tasks

On Mon, 23 Jun 2025 19:59:11 +0800
Jiazi Li <jqqlijiazi@...il.com> wrote:

> Tasks with PF_USER_WORKER flag also only run in kernel space,
> so do not trace user stack for these tasks.

What exactly is the difference between PF_KTHREAD and PF_USER_WORKER?

Has all the locations that test for PF_KTHREAD been audited to make
sure that PF_USER_WORKER isn't also needed?

I'm working on other code that needs to differentiate between user
tasks and kernel tasks, and having to have multiple flags to test is
becoming quite a burden.

-- Steve


> 
> Signed-off-by: Jiazi Li <jqqlijiazi@...il.com>
> Signed-off-by: peixuan.qiu <peixuan.qiu@...nssion.com>
> ---
>  kernel/stacktrace.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
> index afb3c116da91..82fbccdd1a24 100644
> --- a/kernel/stacktrace.c
> +++ b/kernel/stacktrace.c
> @@ -228,8 +228,8 @@ unsigned int stack_trace_save_user(unsigned long *store, unsigned int size)
>  		.size	= size,
>  	};
>  
> -	/* Trace user stack if not a kernel thread */
> -	if (current->flags & PF_KTHREAD)
> +	/* Skip tasks that do not return to userspace */
> +	if (current->flags & (PF_KTHREAD | PF_USER_WORKER))
>  		return 0;
>  
>  	arch_stack_walk_user(consume_entry, &c, task_pt_regs(current));