linux-kernel - Re: Perf: WARNING: arch/x86/entry/common.c:624 idtentry_exit_cond

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Message-ID: <87imfwd5f6.fsf@nanos.tec.linutronix.de>
Date:   Fri, 12 Jun 2020 11:01:01 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        open list <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, cj.chengjian@...wei.com,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michel Lespinasse <walken@...gle.com>,
        lkft-triage@...ts.linaro.org,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: Perf: WARNING: arch/x86/entry/common.c:624 idtentry_exit_cond_rcu+0x92/0xc0

Andy Lutomirski <luto@...nel.org> writes:
> On Thu, Jun 11, 2020 at 4:22 PM Andy Lutomirski <luto@...nel.org> wrote:
>
> Two bugs here.
>
> 1. We had an issue with WARN. Patch sent.

Grabbed it

> 2. idtentry.h has, for x86_32:
>
> # define DEFINE_IDTENTRY_IST  DEFINE_IDTENTRY
>
> This is nonsense.  It's getting late over here and I'd rather focus on
> the more interesting RCU issue, so that's all from me today.

Well, this might be nonsense, but it's exactly matching the current code
in mainline which, e.g. for #DB does:

SYM_CODE_START(debug)
	/*
	 * Entry from sysenter is now handled in common_exception
	 */
	ASM_CLAC
	pushl	$0
	pushl	$do_debug
	jmp	common_exception
SYM_CODE_END(debug)

There is no IST on 32bit, never was. We do software stack switching for
device interrupts, but that's a different story.

Thanks,

        tglx