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    SubjectRe: [patch V4 part 1 05/36] x86/entry: Flip _TIF_SIGPENDING and _TIF_NOTIFY_RESUME handling
    ----- 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.
    http://www.efficios.com

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