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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.googlemail.com with ESMTPSA id e6-20020a170906314600b00781be3e7badsm12131965eje.53.2023.01.16.09.36.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Jan 2023 09:36:44 -0800 (PST) Message-ID: <456f6c15-3043-6da2-349d-c0c3880c1a55@redhat.com> Date: Mon, 16 Jan 2023 18:36:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH 2/3] rcu: Equip sleepable RCU with lockdep dependency graph checks Content-Language: en-US To: paulmck@kernel.org, Boqun Feng Cc: linux-kernel@vger.kernel.org, rcu@vger.kernel.org, kvm@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Lai Jiangshan , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , David Woodhouse , seanjc@google.com, Joel Fernandes , Matthew Wilcox , Michal Luczaj References: <20230113065955.815667-1-boqun.feng@gmail.com> <20230113065955.815667-3-boqun.feng@gmail.com> <20230113112949.GX4028633@paulmck-ThinkPad-P17-Gen-1> <20230113191120.GB4028633@paulmck-ThinkPad-P17-Gen-1> From: Paolo Bonzini In-Reply-To: <20230113191120.GB4028633@paulmck-ThinkPad-P17-Gen-1> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/13/23 20:11, Paul E. McKenney wrote: > On Fri, Jan 13, 2023 at 10:05:22AM -0800, Boqun Feng wrote: >> On Fri, Jan 13, 2023 at 03:29:49AM -0800, Paul E. McKenney wrote: >> I prefer that the first two patches go through your tree, because it >> reduces the synchronization among locking, rcu and KVM trees to the >> synchronization betwen rcu and KVM trees. > > Very well, I have queued and pushed these with the usual wordsmithing, > thank you! I'm worried about this case: CPU 0 CPU 1 -------------------- ------------------ lock A srcu lock B srcu lock B lock A srcu unlock B unlock A unlock A srcu unlock B While a bit unclean, there is nothing that downright forbids this; as long as synchronize_srcu does not happen inside lock A, no deadlock can occur. However, if srcu is replaced with an rwlock then lockdep should and does report a deadlock. Boqun, do you get a false positive or do your patches correctly suppress this? Paolo