From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 05E91481AB for ; Fri, 5 Jul 2024 08:11:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720167074; cv=none; b=KsadiXFI80S/cIla21efV+7sVVqC0xZCEMQNEkZiMjvif3g0A7shXkijCUjJDll2ObVcrUha1yD+GWjO3Uk21HHga2F8q4oMYuye0FiZ31Nf6e+wjgvTuECKHN9TPXheRkA/mxgDE1R4/ROK7k/X4RCsbyBBxk7ScCEo8lf7Bpk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720167074; c=relaxed/simple; bh=gBqPfmddrH/OaT/vComJkfGDX4lFxIXlD55M1/sZb0g=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WFe53pyD3+Tgq0sVnpwnqaml9yDmaTNSSK0Ph//7W554KaiAxOgf7iyHpDGgg2Qw4kVIQg2/ZkjK7OBHn4wfhZRdsoa1JfDkVUlxTFVDMCkt4jgabnzGaNMG/g/p+xItV+zxglg+Ekij5ppLLgOyeKl3W+Mna4AqV1Imp7tzHEk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=m+iYVyTe; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="m+iYVyTe" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=fTspDeJXWYWa25zTECERqTETokK/MNLva0Gqhr5gqqY=; b=m+iYVyTey7Jm9MaPKUbsk91cox w6+heyZqJrc8j4c/eSjQPBxqZLL9ngfPG5t/wPhdWihp2CNPzt+HOY26+s1ZRV9rEs0AoPe/F09yX j8r8naa+k/YLGcQtfYFJSnMv8fgy/txqh+Cxv2TF8k68cUMiVhDBBdwdD9xVACK8HW/3RDFIbdXCB 7MQMf0/Ey+gOj7awGCWyuZ1M2x8+rBhMQRsP9G+4TegfS9cQ/PEB8l4wO9WENnZjBvZjCBPoGMge+ nRPZBB0OfrbGESrd/T5kHrecbca87MFyA5lgMxgflJen4S7PD2h4poF2ITQh+uU9Me3xu1hbch5jq bJ9n3u0g==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.97.1 #2 (Red Hat Linux)) id 1sPe1t-0000000AJ0T-0vz7; Fri, 05 Jul 2024 08:10:53 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id B6F493005AF; Fri, 5 Jul 2024 10:10:52 +0200 (CEST) Date: Fri, 5 Jul 2024 10:10:52 +0200 From: Peter Zijlstra To: Radoslaw Zielonek Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, oleg@redhat.com, brauner@kernel.org, akpm@linux-foundation.org, tandersen@netflix.com, bigeasy@linutronix.de, vincent.whitchurch@axis.com, kunyu@nfschina.com, ardb@kernel.org, linux-kernel@vger.kernel.org, liam.howlett@oracle.com, syzbot+a941018a091f1a1f9546@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com Subject: Re: [RFC] Signaling overhead on RT tasks is causing RCU stall Message-ID: <20240705081052.GA11386@noisy.programming.kicks-ass.net> References: <20240705075622.925325-2-radoslaw.zielonek@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240705075622.925325-2-radoslaw.zielonek@gmail.com> On Fri, Jul 05, 2024 at 09:56:23AM +0200, Radoslaw Zielonek wrote: > Hello, > > I'm working on syzbot bug: rcu detected stall in validate_mm > https://syzkaller.appspot.com/bug?extid=a941018a091f1a1f9546. > I have analyzed this issue and here is what I found: > > When too many signals are sent to the RT task, the overhead becomes very high. > The task cannot perform its job and as a consquenece the rt_runtime (0.95s) > is not reached even after hundreds of seconds. I'm having trouble parsing this. What overhead becomes high? Is the task spending time in-kernel? Because if the task is spending time in-user handling all its signals, it should accumulate runtime just fine. That is, your analysis seems to leave out / gloss over the important bit.