From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D6354C433E0 for ; Mon, 29 Mar 2021 12:09:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A86FE61864 for ; Mon, 29 Mar 2021 12:09:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231725AbhC2MIr (ORCPT ); Mon, 29 Mar 2021 08:08:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42744 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231731AbhC2MIa (ORCPT ); Mon, 29 Mar 2021 08:08:30 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E82BAC061574; Mon, 29 Mar 2021 05:08:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Njn/KvV5Snuv3RW7HAFUHdZEr2iaxCFGr7M1vBWlqyE=; b=HItK73o0bQo72HLTdxmUfNE+Tx 5RC7H0/B82q23CUYsvFs3+5H8CYap7vGcfq0YcTFFhKd5km8DdGvhmT4fnKoYz9ZE3vucoJ+2e5Rj mZG4oju+VZl5ri5ckYwXVae1tbFoFCSmsPqAvAJW48MZmiws+JLzDkUENY9Z45KTju7JPqvLLaChv pRyQfWKopxnNivlzrjrXRhnUXf43yDuNsAoPHohWhLRzhmg19LtEKMgjX25v9t2cgNfwDMtidlkw0 xR56RxWS6dOWGRZolAj79Ss/uzt26prrNSUD+nrBUUQJq6ffU99UownAzF74gEXF3/xIqrE09E6Qv jeMw0Dxw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1lQqfm-001WyJ-TV; Mon, 29 Mar 2021 12:07:18 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id D5B5B304B90; Mon, 29 Mar 2021 14:07:09 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9D5F52071A3CB; Mon, 29 Mar 2021 14:07:09 +0200 (CEST) Date: Mon, 29 Mar 2021 14:07:09 +0200 From: Peter Zijlstra To: Marco Elver Cc: alexander.shishkin@linux.intel.com, acme@kernel.org, mingo@redhat.com, jolsa@redhat.com, mark.rutland@arm.com, namhyung@kernel.org, tglx@linutronix.de, glider@google.com, viro@zeniv.linux.org.uk, arnd@arndb.de, christian@brauner.io, dvyukov@google.com, jannh@google.com, axboe@kernel.dk, mascasa@google.com, pcc@google.com, irogers@google.com, kasan-dev@googlegroups.com, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-kselftest@vger.kernel.org, Oleg Nesterov , Jiri Olsa Subject: Re: [PATCH v3 06/11] perf: Add support for SIGTRAP on perf events Message-ID: References: <20210324112503.623833-1-elver@google.com> <20210324112503.623833-7-elver@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Mar 25, 2021 at 09:14:39AM +0100, Marco Elver wrote: > On Wed, Mar 24, 2021 at 12:24PM +0100, Marco Elver wrote: > [...] > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index b6434697c516..1e4c949bf75f 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -6391,6 +6391,17 @@ void perf_event_wakeup(struct perf_event *event) > > } > > } > > > > +static void perf_sigtrap(struct perf_event *event) > > +{ > > + struct kernel_siginfo info; > > + > > I think we need to add something like this here: > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 4b82788fbaab..4fcd6b45ce66 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -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; > + > clear_siginfo(&info); > info.si_signo = SIGTRAP; > info.si_code = TRAP_PERF; > > 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. But also, I think Jiri Olsa was going to poke around here because all of this is broken on PREEMPT_RT. IIRC the plan was to add yet another stage to the construct. So where today we have: irq_work_queue() ... perf_pending_event() (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) The idea was, I think to add a task_work(), such that we get: irq_work_queue() ... perf_pending_event() task_work_add() run_task_work() ... kill_fasync();