linux-kernel - Re: [PATCH v5 1/8] smp: Run functions concurrently in smp_call_function_many

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Date:   Wed, 17 Feb 2021 01:02:41 +0000
From:   Nadav Amit <namit@...are.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Rik van Riel <riel@...riel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v5 1/8] smp: Run functions concurrently in
 smp_call_function_many_cond()

> On Feb 16, 2021, at 10:59 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Tue, Feb 16, 2021 at 06:53:09PM +0000, Nadav Amit wrote:
>>> On Feb 16, 2021, at 8:32 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
>>> I'm not sure I can explain it yet. It did get me looking at
>>> on_each_cpu() and it appears that wants to be converted too, something
>>> like the below perhaps.
>> 
>> Looks like a good cleanup, but I cannot say I understand the problem and how
>> it would solve it. Err...
> 
> Yeah, me neither. Bit of a mystery so far.

This stall seems to be real. Intuitively I presumed preemption was
mistakenly enabled, but it does not seem so.

Any chance you can build the kernel with “CONFIG_CSD_LOCK_WAIT_DEBUG=Y” and
rerun it? Perhaps that output will tell us more.