From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F01382C864; Thu, 4 Jan 2024 22:36:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kis75KjI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1E3DDC433C7; Thu, 4 Jan 2024 22:36:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1704407760; bh=Mq+r79RdBVvYAqCrZWo4Leoc5n8LdXkzjBvT3jhBw/A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kis75KjIBAdoH6slBkerUwHzk9zUXO0G04RfMEuEk2X+c5Du3iw2K/KQv55UmHY8k bY/934IZnoI6+n6IsqsIkw+En/qAGHwYZsqK1x5GmFMp3ey4F5ni8M05TixO6OHLlE FAylxetipST9QoFHvWO0cQN80awy09tkjlna0sSjGv3oWTM8z1b2DP2FkGwinMPrO/ Rtr3SyxoK/wqZj5glCXiEduhwUsMktZkVPxw0jYPSXrhqw88vfjb8SIJ+kJi01zpKM XT/doh6UHi1bVHwKsNDNo2K7kit7MyGmcVrRWxllA2Fe+AjXLyOjQRjeemKKp/5KLB /KcLlwnJJixNg== Received: by quaco.ghostprotocols.net (Postfix, from userid 1000) id 83A8A403EF; Thu, 4 Jan 2024 19:35:57 -0300 (-03) Date: Thu, 4 Jan 2024 19:35:57 -0300 From: Arnaldo Carvalho de Melo To: Sebastian Andrzej Siewior Cc: Mike Galbraith , Peter Zijlstra , Marco Elver , linux-rt-users@vger.kernel.org, Linux Kernel Mailing List , Juri Lelli , Clark Williams , Alessandro Carminati , Thomas Gleixner Subject: Re: 'perf test sigtrap' failing on PREEMPT_RT_FULL Message-ID: References: <20230728150718.8odZX-jD@linutronix.de> Precedence: bulk X-Mailing-List: linux-rt-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230728150718.8odZX-jD@linutronix.de> X-Url: http://acmel.wordpress.com Em Fri, Jul 28, 2023 at 05:07:18PM +0200, Sebastian Andrzej Siewior escreveu: > On 2023-07-26 08:10:45 [+0200], Mike Galbraith wrote: > > > [   52.848925] BUG: scheduling while atomic: perf/6549/0x00000002 > > Had bf9ad37dc8a not been reverted due to insufficient beauty, you could > > trivially make the sigtrap test a happy camper (wart tested in tip-rt). > Thank you for the pointer Mike. > I guess we need this preempt_disable_notrace() in perf_pending_task() > due to context accounting in get_recursion_context(). Would a > migrate_disable() be sufficient or could we send the signal outside of > the preempt-disabled block? I got back to this, need to go again over all the callers of perf_swevent_get_recursion_context(), from the first quick glance there are other places with preempt_disable()/enable(), but doing just the switch to migrate disable/enable on perf_pending_task() makes this specific test to work: [acme@nine linux]$ git log --oneline -5 086dab66d504 (HEAD -> linux-rt-devel/linux-6.7.y-rt/send_sig_perf.fix, tag: v6.7-rc5-rt5, linux-rt-devel/linux-6.7.y-rt) v6.7-rc5-rt5 29e0d951f39b printk: Update the printk series. 2308ecc8ce88 (tag: v6.7-rc5-rt4) v6.7-rc5-rt4 10d5f3551216 Merge tag 'v6.7-rc5' into linux-6.7.y-rt a39b6ac3781d (tag: v6.7-rc5, linux-rt-devel/master, linux-rt-devel/linux-6.7.y) Linux 6.7-rc5 [acme@nine linux]$ git diff diff --git a/kernel/events/core.c b/kernel/events/core.c index c9d123e13b57..a9b9ef60f6b3 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6801,7 +6801,7 @@ static void perf_pending_task(struct callback_head *head) * If we 'fail' here, that's OK, it means recursion is already disabled * and we won't recurse 'further'. */ - preempt_disable_notrace(); + migrate_disable(); rctx = perf_swevent_get_recursion_context(); if (event->pending_work) { @@ -6812,7 +6812,7 @@ static void perf_pending_task(struct callback_head *head) if (rctx >= 0) perf_swevent_put_recursion_context(rctx); - preempt_enable_notrace(); + migrate_enable(); put_event(event); } [acme@nine linux]$ uname -a Linux nine 6.7.0-rc5-rt5.sigtrap-fix-dirty #2 SMP PREEMPT_RT Thu Jan 4 18:11:44 -03 2024 x86_64 x86_64 x86_64 GNU/Linux [acme@nine linux]$ sudo su - [sudo] password for acme: [root@nine ~]# [root@nine ~]# perf test sigtrap 68: Sigtrap : Ok [root@nine ~]# [root@nine ~]# perf probe -L perf_pending_task 0 static void perf_pending_task(struct callback_head *head) { 2 struct perf_event *event = container_of(head, struct perf_event, pending_task); 3 int rctx; /* * If we 'fail' here, that's OK, it means recursion is already disabled * and we won't recurse 'further'. */ migrate_disable(); 10 rctx = perf_swevent_get_recursion_context(); 12 if (event->pending_work) { 13 event->pending_work = 0; 14 perf_sigtrap(event); 15 local_dec(&event->ctx->nr_pending); } 18 if (rctx >= 0) 19 perf_swevent_put_recursion_context(rctx); 20 migrate_enable(); 22 put_event(event); } #ifdef CONFIG_GUEST_PERF_EVENTS [root@nine ~]# perf probe perf_pending_task Added new event: probe:perf_pending_task (on perf_pending_task) You can now use it in all perf tools, such as: perf record -e probe:perf_pending_task -aR sleep 1 [root@nine ~]# perf trace --max-events=1 -e probe:perf_pending_task/max-stack=6/ perf test sigtrap 68: Sigtrap : Ok 0.000 :9608/9608 probe:perf_pending_task(__probe_ip: -2064408784) perf_pending_task ([kernel.kallsyms]) task_work_run ([kernel.kallsyms]) exit_to_user_mode_loop ([kernel.kallsyms]) exit_to_user_mode_prepare ([kernel.kallsyms]) irqentry_exit_to_user_mode ([kernel.kallsyms]) asm_sysvec_irq_work ([kernel.kallsyms]) [root@nine ~]# [root@nine ~]# head -5 /etc/os-release NAME="Red Hat Enterprise Linux" VERSION="9.2 (Plow)" ID="rhel" ID_LIKE="fedora" VERSION_ID="9.2" [root@nine ~]# I did the test without the above patch and the original problem is reproduced. > This is also used in perf_pending_irq() and on PREEMPT_RT this is > invoked from softirq context which is preemptible. Right. - Arnaldo