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

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Message-ID: <20190501155711.GB30235@redhat.com>
Date:   Wed, 1 May 2019 17:57:11 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Sudeep Holla <sudeep.holla@....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 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.

> 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.

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

Oleg.