Messages in this thread Patch in this message | | | Date | Wed, 13 May 2020 18:48:06 -0400 (EDT) | From | Mathieu Desnoyers <> | Subject | Re: [patch V4 part 1 05/36] x86/entry: Flip _TIF_SIGPENDING and _TIF_NOTIFY_RESUME handling |
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----- On May 13, 2020, at 5:10 PM, rostedt rostedt@goodmis.org wrote:
> On Wed, 13 May 2020 16:56:41 -0400 (EDT) > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > >> ----- 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); > > Looking deeper into this, it appears that do_signal() can freeze or kill the > task. > > That is, it wont go back to user space here, but simply schedule out (being > traced) or even exit (killed). > > Before the resume hooks would never be called in such cases, and now they > are.
Regarding swapping order of tracehook vs do_signal: Is the task really resumed if it gets frozen or killed ? What is this change trying to accomplish, why is it needed in the first place ?
Regarding swapping order of rseq wrt do_signal: why is it needed, why, and has this been tested ?
Thanks,
Mathieu
> > -- Steve > > >> > + >> > if (cached_flags & _TIF_USER_RETURN_NOTIFY) >> > fire_user_return_notifiers();
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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