linux-kernel - Re: [PATCH v2 3/6] x86: clean up _TIF_SYSCALL_EMU handling using ptrace_syscall

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Date:   Wed, 1 May 2019 17:51:51 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Richard Weinberger <richard@....at>, jdike@...toit.com,
        Steve Capper <Steve.Capper@....com>,
        Haibo Xu <haibo.xu@....com>, Bin Lu <bin.lu@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v2 3/6] x86: clean up _TIF_SYSCALL_EMU handling using
 ptrace_syscall_enter hook

On Wed, May 01, 2019 at 05:57:11PM +0200, Oleg Nesterov wrote:
> On 04/30, Sudeep Holla wrote:
> >
> > On Mon, Mar 18, 2019 at 04:33:22PM +0100, Oleg Nesterov wrote:
> > >
> > > And it seems that _TIF_WORK_SYSCALL_ENTRY needs some cleanups too... We don't need
> > > "& _TIF_WORK_SYSCALL_ENTRY" in syscall_trace_enter, and _TIF_WORK_SYSCALL_ENTRY
> > > should not include _TIF_NOHZ?
> > >
> >
> > I was about to post the updated version and checked this to make sure I have
> > covered everything or not. I had missed the above comment. All architectures
> > have _TIF_NOHZ in their mask that they check to do work. And from x86, I read
> > "...syscall_trace_enter(). Also includes TIF_NOHZ for enter_from_user_mode()"
> > So I don't understand why _TIF_NOHZ needs to be dropped.
>
> I have already forgot this discussion... But after I glanced at this code again
> I still think the same, and I don't understand why do you disagree.
>

Sorry, but I didn't have any disagreement, I just said I don't understand
the usage on all architectures at that moment.

> > Also if we need to drop, we can address that separately examining all archs.
>
> Sure, and I was only talking about x86. We can keep TIF_NOHZ and even
> set_tsk_thread_flag(TIF_NOHZ) in context_tracking_cpu_set() if some arch needs
> this but remove TIF_NOHZ from TIF_WORK_SYSCALL_ENTRY in arch/x86/include/asm/thread_info.h,
> afaics this shouldn't make any difference.
>

OK, it's just x86, then I understand your point. I was looking at all
the architectures, sorry for the confusion.

> And I see no reason why x86 needs to use TIF_WORK_SYSCALL_ENTRY in
> syscall_trace_enter().
>

Agreed

--
Regards,
Sudeep