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Fri, 20 Aug 2021 04:11:19 +0000 (UTC) Received: from ovpn-113-78.phx2.redhat.com (ovpn-113-78.phx2.redhat.com [10.3.113.78]) by smtp.corp.redhat.com (Postfix) with ESMTP id EA11A189C4; Fri, 20 Aug 2021 04:11:12 +0000 (UTC) Message-ID: <561ab28b18c31fbc221f4cb0c4df6db9b0538675.camel@redhat.com> Subject: Re: [PATCH] rcutorture: Avoid problematic critical section nesting on RT From: Scott Wood To: paulmck@kernel.org, Sebastian Andrzej Siewior Cc: Valentin Schneider , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, rcu@vger.kernel.org, linux-rt-users@vger.kernel.org, Catalin Marinas , Will Deacon , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Steven Rostedt , Daniel Bristot de Oliveira , Frederic Weisbecker , Josh Triplett , Mathieu Desnoyers , Davidlohr Bueso , Lai Jiangshan , Joel Fernandes , Anshuman Khandual , Vincenzo Frascino , Steven Price , Ard Biesheuvel , Boqun Feng , Mike Galbraith Date: Thu, 19 Aug 2021 23:11:12 -0500 In-Reply-To: <20210819182035.GF4126399@paulmck-ThinkPad-P17-Gen-1> References: <20210811201354.1976839-1-valentin.schneider@arm.com> <20210811201354.1976839-2-valentin.schneider@arm.com> <20210817121345.5iyj5epemczn3a52@linutronix.de> <20210817131741.evduh4fw7vyv2dzt@linutronix.de> <20210817144018.nqssoq475vitrqlv@linutronix.de> <20210818224651.GY4126399@paulmck-ThinkPad-P17-Gen-1> <20210819153927.clqxr4f7qegpflbr@linutronix.de> <20210819154708.3efz6jtgwtuhpeds@linutronix.de> <20210819182035.GF4126399@paulmck-ThinkPad-P17-Gen-1> Organization: Red Hat User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210819_211130_500718_C785905E X-CRM114-Status: GOOD ( 24.41 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 2021-08-19 at 11:20 -0700, Paul E. McKenney wrote: > On Thu, Aug 19, 2021 at 05:47:08PM +0200, Sebastian Andrzej Siewior wrote: > > On 2021-08-19 17:39:29 [+0200], To Paul E. McKenney wrote: > > > + /* > > > + * Ideally these sequences would be detected in debug builds > > > + * (regardless of RT), but until then don't stop testing > > > + * them on non-RT. > > > + */ > > > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { > > > + /* > > > + * Can't release the outermost rcu lock in an irq disabled > > > + * section without preemption also being disabled, if irqs > > > + * had ever been enabled during this RCU critical section > > > + * (could leak a special flag and delay reporting the qs). > > > + */ > > > + if ((oldmask & RCUTORTURE_RDR_RCU) && > > > + (mask & RCUTORTURE_RDR_IRQ) && > > > + !(mask & preempts)) > > > + mask |= RCUTORTURE_RDR_RCU; > > > > This piece above, I don't understand. I had it running for a while and > > it didn't explode. Let me try TREE01 for 30min without that piece. > > This might be historical. There was a time when interrupts being > disabled across rcu_read_unlock() meant that preemption had to have > been disabled across the entire RCU read-side critical section. > > I am not seeing a purpose for it now, but I could easily be missing > something, especially given my tenuous grasp of RT. Yeah, I think this was to deal with not having the irq work stuff in RT at the time. -Scott _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel