Re: [PATCH] perf: Fix oops when kthread execs user process

[Will Deacon]

On Wed, May 29, 2019 at 03:25:15PM +0200, Peter Zijlstra wrote:
> On Wed, May 29, 2019 at 02:05:21PM +0100, Will Deacon wrote:
> > On Wed, May 29, 2019 at 02:55:57PM +0200, Peter Zijlstra wrote:
> 
> > >  	if (user_mode(regs)) {
> > 
> > Hmm, so it just occurred to me that Mark's observation is that the regs
> > can be junk in some cases. In which case, should we be checking for
> > kthreads first?
> 
> task_pt_regs() can return garbage, but @regs is the exception (or
> perf_arch_fetch_caller_regs()) regs, and for those user_mode() had
> better be correct.

So what should we report for the idle task?

Will