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Message-ID: <20210329142705.GA24849@redhat.com>
Date: Mon, 29 Mar 2021 16:27:06 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Marco Elver <elver@...gle.com>, alexander.shishkin@...ux.intel.com,
acme@...nel.org, mingo@...hat.com, jolsa@...hat.com,
mark.rutland@....com, namhyung@...nel.org, tglx@...utronix.de,
glider@...gle.com, viro@...iv.linux.org.uk, arnd@...db.de,
christian@...uner.io, dvyukov@...gle.com, jannh@...gle.com,
axboe@...nel.dk, mascasa@...gle.com, pcc@...gle.com,
irogers@...gle.com, kasan-dev@...glegroups.com,
linux-arch@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, x86@...nel.org,
linux-kselftest@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v3 06/11] perf: Add support for SIGTRAP on perf events
On 03/29, Peter Zijlstra wrote:
>
> On Thu, Mar 25, 2021 at 09:14:39AM +0100, Marco Elver wrote:
> > @@ -6395,6 +6395,13 @@ static void perf_sigtrap(struct perf_event *event)
> > {
> > struct kernel_siginfo info;
> >
> > + /*
> > + * This irq_work can race with an exiting task; bail out if sighand has
> > + * already been released in release_task().
> > + */
> > + if (!current->sighand)
> > + return;
This is racy. If "current" has already passed exit_notify(), current->parent
can do release_task() and destroy current->sighand right after the check.
> Urgh.. I'm not entirely sure that check is correct, but I always forget
> the rules with signal. It could be we ought to be testing PF_EXISTING
> instead.
Agreed, PF_EXISTING check makes more sense in any case, the exiting task
can't receive the signal anyway.
Oleg.
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