linux-kernel - Re: [PATCH v3 06/11] perf: Add support for SIGTRAP on perf events

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Message-ID: <CANpmjNPGmzzg-uv3DGZ+1M+nDNy3WiFU7g3u_CzR-GBju+1Z_Q@mail.gmail.com>
Date:   Wed, 31 Mar 2021 18:50:12 +0200
From:   Marco Elver <elver@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexander Potapenko <glider@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian@...uner.io>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jann Horn <jannh@...gle.com>, Jens Axboe <axboe@...nel.dk>,
        Matt Morehouse <mascasa@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Ian Rogers <irogers@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, Oleg Nesterov <oleg@...hat.com>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v3 06/11] perf: Add support for SIGTRAP on perf events

On Wed, 31 Mar 2021 at 16:51, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Mar 31, 2021 at 02:32:58PM +0200, Marco Elver wrote:
> > On Mon, 29 Mar 2021 at 14:07, Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > > (and we might already have a problem on some architectures where there
> > > can be significant time between these due to not having
> > > arch_irq_work_raise(), so ideally we ought to double check current in
> > > your case)
> >
> > I missed this bit -- just to verify: here we want to check that
> > event->ctx->task == current, in case the the irq_work runs when the
> > current task has already been replaced. Correct?
>
> Yeah, just not sure what a decent failure would be, silent ignore seems
> undesired, maybe WARN and archs that can trigger it get to fix it ?

I'll go with a WARN and add a comment.

This also revealed there should be a requirement that sigtrap events
must be associated with a task (syzkaller managed to trigger the
warning for cpu events).

Thanks,
-- Marco