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In-Reply-To: <20200126025225.GA20804@agluck-desk2.amr.corp.intel.com>
From:   Tony Luck <tony.luck@gmail.com>
Date:   Sun, 26 Jan 2020 18:05:05 -0800
Message-ID: <CA+8MBbKah37goKsCxJoSD-xF7ZchKfWu0n27rN04UYiOCeXXBQ@mail.gmail.com>
Subject: Re: [PATCH v15] x86/split_lock: Enable split lock detection by kernel
To:     Arvind Sankar <nivedita@alum.mit.edu>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Yu, Fenghua" <fenghua.yu@intel.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        H Peter Anvin <hpa@zytor.com>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "Shankar, Ravi V" <ravi.v.shankar@intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
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On Sat, Jan 25, 2020 at 6:53 PM Luck, Tony <tony.luck@intel.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