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[209.85.208.173]) by smtp.gmail.com with ESMTPSA id p76sm4491097ljb.63.2019.04.23.13.45.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Apr 2019 13:45:34 -0700 (PDT) Received: by mail-lj1-f173.google.com with SMTP id h21so14721303ljk.13 for ; Tue, 23 Apr 2019 13:45:33 -0700 (PDT) X-Received: by 2002:a2e:9213:: with SMTP id k19mr897555ljg.118.1556052333576; Tue, 23 Apr 2019 13:45:33 -0700 (PDT) MIME-Version: 1.0 References: <20190419131522.GW14281@hirez.programming.kicks-ass.net> <57620139-92a3-4a21-56bd-5d6fff23214f@redhat.com> <7b1bfc26-6e90-bd65-ab46-08413acd80e9@redhat.com> <20190423141714.GO11158@hirez.programming.kicks-ass.net> <4f62d7f2-e5f6-500e-3e70-b1d1978f7140@redhat.com> <20190423193435.GX4038@hirez.programming.kicks-ass.net> <88ba7be0-9ec5-941e-1b3f-80fbe05fe3a0@redhat.com> <20190423195559.GY4038@hirez.programming.kicks-ass.net> <20190423203512.GB4038@hirez.programming.kicks-ass.net> In-Reply-To: <20190423203512.GB4038@hirez.programming.kicks-ass.net> From: Linus Torvalds Date: Tue, 23 Apr 2019 13:45:17 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] bpf: Fix preempt_enable_no_resched() abuse To: Peter Zijlstra Cc: Waiman Long , Ingo Molnar , Will Deacon , Thomas Gleixner , Linux List Kernel Mailing , "the arch/x86 maintainers" , Davidlohr Bueso , Tim Chen , huang ying , Roman Gushchin , Alexei Starovoitov , Daniel Borkmann Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 23, 2019 at 1:35 PM Peter Zijlstra wrote: > > That one 'funnily' doesn't actually work; cond_resched() is a no-op on > PREEMPT=y. Uhhuh. I "knew" that, but it's one of those bitrotting things. Which does make your argument stronger, of course. This is way too easy to get wrong even if you think you are being careful. I guess it could be another thing to check for with objtool, since you have now gotten the experience with it ;) Linus