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[46.139.12.213]) by smtp.gmail.com with ESMTPSA id t19sm12144418wmi.29.2019.08.19.01.52.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Aug 2019 01:52:16 -0700 (PDT) Date: Mon, 19 Aug 2019 10:52:13 +0200 From: Ingo Molnar To: Mark Rutland Cc: Geert Uytterhoeven , Linux Kernel Mailing List , Andi Kleen , Andrew Morton , Sebastian Andrzej Siewior , Borislav Petkov , Catalin Marinas , "David S. Miller" , Christoph Hellwig , kan.liang@intel.com, Peter Zijlstra , Rik van Riel , Will Deacon Subject: Re: [PATCH 1/9] sched/core: add is_kthread() helper Message-ID: <20190819085213.GA15409@gmail.com> References: <20190814104131.20190-1-mark.rutland@arm.com> <20190814104131.20190-2-mark.rutland@arm.com> <20190814113232.GE17931@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190814113232.GE17931@lakrids.cambridge.arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Mark Rutland wrote: > On Wed, Aug 14, 2019 at 01:26:43PM +0200, Geert Uytterhoeven wrote: > > Hi Mark, > > > > On Wed, Aug 14, 2019 at 12:43 PM Mark Rutland wrote: > > > Code checking whether a task is a kthread isn't very consistent. Some > > > code correctly tests task->flags & PF_THREAD, while other code checks > > > task->mm (which can be true for a kthread which calls use_mm()). > > > > > > So that we can clean this up and keep the code easy to follow, let's add > > > an obvious helper function to test whether a task is a kthread. > > > Subsequent patches will use this as part of cleaning up and correcting > > > open-coded tests. > > > > > > At the same time, let's fix up the kerneldoc for is_idle_task() for > > > consistency with the new helper, using true/false rather than 0/1, given > > > the functions return bool. > > > > > > Signed-off-by: Mark Rutland > > > > Thanks for your patch! > > > > > --- a/include/linux/sched.h > > > +++ b/include/linux/sched.h > > > @@ -1621,13 +1621,24 @@ extern struct task_struct *idle_task(int cpu); > > > * is_idle_task - is the specified task an idle task? > > > * @p: the task in question. > > > * > > > - * Return: 1 if @p is an idle task. 0 otherwise. > > > + * Return: true if @p is an idle task, false otherwise. > > > */ > > > static inline bool is_idle_task(const struct task_struct *p) > > > { > > > return !!(p->flags & PF_IDLE); > > > } > > > > > > +/** > > > + * is_kthread - is the specified task a kthread > > > + * @p: the task in question. > > > + * > > > + * Return: true if @p is a kthread, false otherwise. > > > + */ > > > +static inline bool is_kthread(const struct task_struct *p) > > > +{ > > > + return !!(p->flags & PF_KTHREAD); > > > > The !! is not really needed. > > Probably you followed is_idle_task() above (where it's also not needed). > > Indeed! I'm aware of the implicit bool conversion, but kept that for > consistency. > > Peter, Ingo, do you have a preference? So the !! pattern is useful where the return value is an integer (i.e. there's a risk of non-bool use) - but the return value is an explicit bool here, so !! is IMO an entirely superfluous obfuscation. Should probably be fixed for is_idle_task() as well? Thanks, Ingo