linux-kernel - Re: [patch V9 10/39] x86/entry: Provide helpers for execute on irqstack

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Message-ID: <87zh9cnfmg.fsf@nanos.tec.linutronix.de>
Date:   Tue, 09 Jun 2020 22:33:43 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Qian Cai <cai@....pw>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        Alexander Potapenko <glider@...gle.com>
Subject: Re: [patch V9 10/39] x86/entry: Provide helpers for execute on irqstack

Qian,

Qian Cai <cai@....pw> writes:
> On Tue, Jun 09, 2020 at 12:20:06AM +0200, Thomas Gleixner wrote:
>> Note, that I doubled the size of the stack depot so that we get real
>> numbers and not the cutoff by the size limit. IOW, the warning should
>> not trigger anymore. If it triggers nevertheless then the numbers will
>> still tell us an interesting story.
>
> Instead of running the whole testsuite, I just picked this single LTP
> oom02 test which seems usually trigger it within the testsuite. Let me
> know if this is insufficient (which indeed tell the big difference in
> "Unique stacks"), and I am happy to run the whole things.

thanks for providing the data.

> BAD: next-20200608
> GOOD: next-20200528 (which does not include this series)
>
> BAD (after boot)
> # cat /sys/kernel/debug/stackdepot/info
> Unique stacks: 33547
> Depot index:   359
> Depot offset:  6752
>
> BAD (after oom02)
> # cat /sys/kernel/debug/stackdepot/info
> Unique stacks: 140476

That's indeed odd. I try to reproduce and figure out what really breaks
here.

Thanks,

        tglx