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[209.85.167.45]) by smtp.gmail.com with ESMTPSA id s18-20020a2e9c12000000b002b9ef00b10csm355966lji.2.2023.09.08.10.15.25 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Sep 2023 10:15:25 -0700 (PDT) Received: by mail-lf1-f45.google.com with SMTP id 2adb3069b0e04-501bd164fbfso3682001e87.0 for ; Fri, 08 Sep 2023 10:15:25 -0700 (PDT) X-Received: by 2002:a05:6512:e9a:b0:4fb:77d6:89c3 with SMTP id bi26-20020a0565120e9a00b004fb77d689c3mr3236491lfb.12.1694193324794; Fri, 08 Sep 2023 10:15:24 -0700 (PDT) MIME-Version: 1.0 References: <20230830184958.2333078-1-ankur.a.arora@oracle.com> <20230830184958.2333078-8-ankur.a.arora@oracle.com> <20230908070258.GA19320@noisy.programming.kicks-ass.net> In-Reply-To: <20230908070258.GA19320@noisy.programming.kicks-ass.net> From: Linus Torvalds Date: Fri, 8 Sep 2023 10:15:07 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED To: Peter Zijlstra Cc: Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, rostedt@goodmis.org, tglx@linutronix.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 3984DA0022 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: g77kfse1qt8dx5kotm3yjnrteczhjqhj X-HE-Tag: 1694193327-493165 X-HE-Meta: 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 zthLvGHZ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 8 Sept 2023 at 00:03, Peter Zijlstra wrote: > > Which on a PREEMPT_COUNT=n build will cause preemption while holding the > spinlock. I think something like the below will cause sufficient > warnings to avoid growing patterns like that. Hmm. I don't think that warning is valid. Disabling preemption is actually fine if it's done in an interrupt, iow if we have allow_resched(); -> irq happens spin_lock(); // Ok and should *not* complain ... spin_unlock(); <- irq return (and preemption) which actually makes me worry about the nested irq case, because this would *not* be ok: allow_resched(); -> irq happens -> *nested* irq happens <- nested irq return (and preemption) ie the allow_resched() needs to still honor the irq count, and a nested irq return obviously must not cause any preemption. I've lost sight of the original patch series, and I assume / hope that the above isn't actually an issue, but exactly because I've lost sight of the original patches and only have this one in my mailbox I wanted to check. Linus