Re: [PATCH] stacktrace: do not trace user stack for user_worker tasks

[Jiazi Li]

On Tue, Jun 24, 2025 at 01:07:44PM -0400, Steven Rostedt wrote:
> On Mon, 23 Jun 2025 19:59:11 +0800
> Jiazi Li <jqqlijiazi@xxxxxxxxx> 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?
> 
I think that apart from never return to user space, PF_USER_WORKER is
basically the same as user space task.
> Has all the locations that test for PF_KTHREAD been audited to make
> sure that PF_USER_WORKER isn't also needed?
> 
No.
> 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.
> 
Yes, so only check both PF_KTHREAD and PF_USER_WORKER before access 
user space stack?
> -- Steve
> 
> 
> > 
> > Signed-off-by: Jiazi Li <jqqlijiazi@xxxxxxxxx>
> > Signed-off-by: peixuan.qiu <peixuan.qiu@xxxxxxxxxxxxx>
> > ---
> >  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));
>