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Peter Anvin" , Jens Axboe , Alasdair Kergon , Mike Snitzer , dm-devel@redhat.com, "David S. Miller" , Jakub Kicinski , Felipe Balbi , Greg Kroah-Hartman , Alexander Viro , Tejun Heo , Zefan Li , Johannes Weiner , Jason Wessel , Daniel Thompson , Douglas Anderson , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , "Rafael J. Wysocki" , Pavel Machek , Will Deacon , Waiman Long , Boqun Feng , Oleg Nesterov , "Paul E. McKenney" , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , John Stultz , Stephen Boyd , Andrew Morton , Paolo Bonzini , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, netdev@vger.kernel.org, linux-usb@vger.kernel.org, linux-fsdevel@vger.kernel.org, cgroups@vger.kernel.org, kgdb-bugreport@lists.sourceforge.net, linux-perf-users@vger.kernel.org, linux-pm@vger.kernel.org, rcu@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org References: <20210602131225.336600299@infradead.org> <20210602133040.271625424@infradead.org> MIME-Version: 1.0 In-Reply-To: <20210602133040.271625424@infradead.org> User-Agent: NeoMutt/20201120 X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-loop: dm-devel@redhat.com X-Mailman-Approved-At: Thu, 03 Jun 2021 02:32:49 -0400 Cc: Juri Lelli , Mark Rutland , Pavel Machek , Mike Snitzer , Alexander Shishkin , kgdb-bugreport@lists.sourceforge.net, Lai Jiangshan , Oleg Nesterov , Ben Segall , linux-mm@kvack.org, dm-devel@redhat.com, Paolo Bonzini , Zefan Li , "H. Peter Anvin" , Joel Fernandes , netdev@vger.kernel.org, Jiri Olsa , Alasdair Kergon , Daniel Thompson , Vincent Guittot , kvm@vger.kernel.org, Will Deacon , cgroups@vger.kernel.org, x86@kernel.org, Ingo Molnar , Mel Gorman , Jakub Kicinski , John Stultz , "Paul E. McKenney" , linux-pm@vger.kernel.org, Boqun Feng , Jason Wessel , Josh Triplett , Steven Rostedt , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, Borislav Petkov , Alexander Viro , Waiman Long , Namhyung Kim , Thomas Gleixner , Arnaldo Carvalho de Melo , Dietmar Eggemann , Jens Axboe , Felipe Balbi , Stephen Boyd , Greg Kroah-Hartman , linux-usb@vger.kernel.org, "Rafael J. Wysocki" , Douglas Anderson , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Johannes Weiner , Tejun Heo , Mathieu Desnoyers , Andrew Morton , rcu@vger.kernel.org, Daniel Bristot de Oliveira , "David S. Miller" Subject: Re: [dm-devel] [PATCH 1/6] sched: Unbreak wakeups X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" On Wed, 02 Jun 2021, Peter Zijlstra wrote: >Remove broken task->state references and let wake_up_process() DTRT. > >The anti-pattern in these patches breaks the ordering of ->state vs >COND as described in the comment near set_current_state() and can lead >to missed wakeups: > > (OoO load, observes RUNNING)<-. > for (;;) { | > t->state = UNINTERRUPTIBLE; | > smp_mb(); ,-----> ,' (OoO load, observed !COND) > | | > | | COND = 1; > | `- if (t->state != RUNNING) > | wake_up_process(t); // not done > if (COND) ---------' > break; > schedule(); // forever waiting > } > t->state = TASK_RUNNING; > >Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Davidlohr Bueso -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel