linux-kernel - Re: [PATCH v15] x86/split_lock: Enable split lock detection by kernel

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Message-ID: <CA+8MBbKah37goKsCxJoSD-xF7ZchKfWu0n27rN04UYiOCeXXBQ@mail.gmail.com>
Date:   Sun, 26 Jan 2020 18:05:05 -0800
From:   Tony Luck <tony.luck@...il.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v15] x86/split_lock: Enable split lock detection by kernel

On Sat, Jan 25, 2020 at 6:53 PM Luck, Tony <tony.luck@...el.com> wrote:

> So why don't we come through __switch_to_xtra() when the spinner
> runs out its time slice (or the udelay interrupt happens and
> preempts the spinner)?

To close out this part of the thread. Linux doesn't call __switch_to_xtra()
in this case because I didn't ask it to. There are separate masks to check
TIF bits for the previous and next tasks in a context switch. I'd only set the
_TIF_SLD bit in the mask for the previous task.

See the v17 I posted a few hours before this message for the fix.

-Tony