Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210324112503.623833-1-elver@google.com> <20210324112503.623833-7-elver@google.com>
 <YFxGb+QHEumZB6G8@elver.google.com> <YGHC7V3bbCxhRWTK@hirez.programming.kicks-ass.net>
 <CANpmjNOPJNhJ2L7cxrvf__tCZpy=+T1nBotKmzr2xMJypd-oJQ@mail.gmail.com> <YGSMXJvLBpQOm3WV@hirez.programming.kicks-ass.net>
In-Reply-To: <YGSMXJvLBpQOm3WV@hirez.programming.kicks-ass.net>
From:   Marco Elver <elver@google.com>
Date:   Wed, 31 Mar 2021 18:50:12 +0200
Message-ID: <CANpmjNPGmzzg-uv3DGZ+1M+nDNy3WiFU7g3u_CzR-GBju+1Z_Q@mail.gmail.com>
Subject: Re: [PATCH v3 06/11] perf: Add support for SIGTRAP on perf events
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alexander Potapenko <glider@google.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        Christian Brauner <christian@brauner.io>,
        Dmitry Vyukov <dvyukov@google.com>,
        Jann Horn <jannh@google.com>, Jens Axboe <axboe@kernel.dk>,
        Matt Morehouse <mascasa@google.com>,
        Peter Collingbourne <pcc@google.com>,
        Ian Rogers <irogers@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        linux-arch <linux-arch@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>, Oleg Nesterov <oleg@redhat.com>,
        Jiri Olsa <jolsa@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, 31 Mar 2021 at 16:51, Peter Zijlstra <peterz@infradead.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@infradead.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