Re: [PATCH v4 34/39] perf: Skip user unwind if !current->mm

[Peter Zijlstra]

On Tue, Jan 21, 2025 at 06:31:26PM -0800, Josh Poimboeuf wrote:
> If the task doesn't have any memory, there's no stack to unwind.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> ---
>  kernel/events/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 99f0f28feeb5..a886bb83f4d0 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7792,7 +7792,7 @@ struct perf_callchain_entry *
>  perf_callchain(struct perf_event *event, struct pt_regs *regs)
>  {
>  	bool kernel = !event->attr.exclude_callchain_kernel;
> -	bool user   = !event->attr.exclude_callchain_user;
> +	bool user   = !event->attr.exclude_callchain_user && current->mm;

What about things like io_uring helpers, don't they keep ->mm but are
never in userspace?