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[209.85.220.65]) by mx.google.com with SMTPS id l71sor10237304pfi.24.2019.02.06.06.36.28 for (Google Transport Security); Wed, 06 Feb 2019 06:36:28 -0800 (PST) Received-SPF: pass (google.com: domain of groeck7@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=tIlWHx60; spf=pass (google.com: domain of groeck7@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=groeck7@gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=HQHBL4H4E6t1GSVT+e5d2e8jbqm9+4cul5BGqspsN2I=; b=tIlWHx60gPrDUm/8WuRcYjBTZtZaZ3gI8BSG6RAbleszT4dI53TmC5ig59sVBeJwVe ildDd5nrv1sQJnZjmSwlubTOCobIj0SIs4JbrlY21ixeBIlgatL0jBB9ijg9EWPXmhm1 5s5pdp0RKzQSfQ1KID5JEUB8NG7kK9dSGtvRleYjZ27wzNDecjBZXmImM6wbzRfR50Px +yUqmLiiHGZ0zWfgNibVQBbGYYE/J5lQ4hO2qTPfPS1NkzcOeYwKIbVa2XQS/sM6INuA WuXpfy+dhdnFrDhE6Y0+owBA0W08jfIpo0YJyUwGknSd0qMT3cZ8+wQzkblyOvVM64Z9 pKmg== X-Google-Smtp-Source: AHgI3IY2mYr+reflHTmYh/rjy9Lup9mpYSVj1qMKfyhuqdXZ3N4QKb0xnCQ/eaqzIaVE3Vq9WBu60w== X-Received: by 2002:a62:c505:: with SMTP id j5mr10781039pfg.149.1549463787859; Wed, 06 Feb 2019 06:36:27 -0800 (PST) Received: from localhost ([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id n73sm9278491pfj.148.2019.02.06.06.36.26 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 06 Feb 2019 06:36:26 -0800 (PST) Date: Wed, 6 Feb 2019 06:36:25 -0800 From: Guenter Roeck To: Tetsuo Handa Cc: Rusty Russell , Chris Metcalf , linux-kernel , Tejun Heo , linux-mm , linux-arch Subject: Re: linux-next: tracebacks in workqueue.c/__flush_work() Message-ID: <20190206143625.GA25998@roeck-us.net> References: <72e7d782-85f2-b499-8614-9e3498106569@i-love.sakura.ne.jp> <87munc306z.fsf@rustcorp.com.au> <201902060631.x166V9J8014750@www262.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201902060631.x166V9J8014750@www262.sakura.ne.jp> User-Agent: Mutt/1.5.24 (2015-08-30) 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 Wed, Feb 06, 2019 at 03:31:09PM +0900, Tetsuo Handa wrote: > (Adding linux-arch ML.) > > Rusty Russell wrote: > > Tetsuo Handa writes: > > > (Adding Chris Metcalf and Rusty Russell.) > > > > > > If NR_CPUS == 1 due to CONFIG_SMP=n, for_each_cpu(cpu, &has_work) loop does not > > > evaluate "struct cpumask has_work" modified by cpumask_set_cpu(cpu, &has_work) at > > > previous for_each_online_cpu() loop. Guenter Roeck found a problem among three > > > commits listed below. > > > > > > Commit 5fbc461636c32efd ("mm: make lru_add_drain_all() selective") > > > expects that has_work is evaluated by for_each_cpu(). > > > > > > Commit 2d3854a37e8b767a ("cpumask: introduce new API, without changing anything") > > > assumes that for_each_cpu() does not need to evaluate has_work. > > > > > > Commit 4d43d395fed12463 ("workqueue: Try to catch flush_work() without INIT_WORK().") > > > expects that has_work is evaluated by for_each_cpu(). > > > > > > What should we do? Do we explicitly evaluate has_work if NR_CPUS == 1 ? > > > > No, fix the API to be least-surprise. Fix 2d3854a37e8b767a too. > > > > Doing anything else would be horrible, IMHO. > > > > Fixing 2d3854a37e8b767a might involve subtle changes. If we do > Why not fix the macros ? #define for_each_cpu(cpu, mask) \ for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask) does not really make sense since it does not evaluate mask. #define for_each_cpu(cpu, mask) \ for ((cpu) = 0; (cpu) < 1 && cpumask_test_cpu((cpu), (mask)); (cpu)++) or something similar might do it. Guenter