Re: [PATCH v5 11/17] perf: Simplify get_perf_callchain() user logic

[Steven Rostedt]

On Thu, 24 Apr 2025 18:36:07 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> > +++ b/kernel/events/callchain.c
> > @@ -246,22 +246,20 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
> >  
> >  	if (user) {
> >  		if (!user_mode(regs)) {
> > -			if  (current->mm)
> > -				regs = task_pt_regs(current);
> > -			else
> > -				regs = NULL;
> > +			if (!current->mm)
> > +				goto exit_put;
> > +			regs = task_pt_regs(current);  
> 
> I'm thinking this might be one of those is-kthread test written as
> has-mm, and they're broken.
> 
> Notably things like the io-uring kthreads do have mm.

Would there ever be a case where:

	current->mm == NULL && !(current->flags & PF_KTHREAD)

?

That is, do we still need to check for current->mm if it's not a kernel
thread, or can we assume it exists?

-- Steve