Re: [patch V4 part 1 05/36] x86/entry: Flip _TIF_SIGPENDING and _TIF_NOTIFY_RESUME handling

Mathieu Desnoyers
2020-05-13T20:56:44Z

----- On May 5, 2020, at 9:16 AM, Thomas Gleixner tglx@linutronix.de wrote:

> Make sure task_work runs before any kind of userspace -- very much
> including signals -- is invoked.

What is missing from this patch description is: _why_ is this deemed
useful ?

Also, color me confused: is "do_signal()" actually running any user-space,
or just setting up the user-space stack for eventual return to signal handler ?

Also, it might be OK, but we're changing the order of two things which
have effects on each other: restartable sequences abort fixup for preemption
and do_signal(), which also have effects on rseq abort.

Because those two will cause the abort to trigger, I suspect changing
the order might be OK, but we really need to think this through.

Thanks,

Mathieu

>
> Suggested-by: Andy Lutomirski <luto@kernel.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/entry/common.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -156,16 +156,16 @@ static void exit_to_usermode_loop(struct
> if (cached_flags & _TIF_PATCH_PENDING)
> klp_update_patch_state(current);
>
> - /* deal with pending signal delivery */
> - if (cached_flags & _TIF_SIGPENDING)
> - do_signal(regs);
> -
> if (cached_flags & _TIF_NOTIFY_RESUME) {
> clear_thread_flag(TIF_NOTIFY_RESUME);
> tracehook_notify_resume(regs);
> rseq_handle_notify_resume(NULL, regs);
> }
>
> + /* deal with pending signal delivery */
> + if (cached_flags & _TIF_SIGPENDING)
> + do_signal(regs);
> +
> if (cached_flags & _TIF_USER_RETURN_NOTIFY)
> fire_user_return_notifiers();

--
Mathieu Desnoyers
EfficiOS Inc.