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[140.211.169.12]) by mx.google.com with ESMTPS id q16si407786pgh.185.2019.02.13.13.37.55 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 13 Feb 2019 13:37:56 -0800 (PST) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) client-ip=140.211.169.12; Authentication-Results: mx.google.com; spf=pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 798361389; Wed, 13 Feb 2019 21:37:55 +0000 (UTC) Date: Wed, 13 Feb 2019 13:37:54 -0800 From: Andrew Morton To: Michal Hocko Cc: Tetsuo Handa , Chris Metcalf , Rusty Russell , linux-mm@kvack.org, Guenter Roeck , Tejun Heo Subject: Re: [PATCH] mm/swap.c: workaround for_each_cpu() bug on UP kernel. Message-Id: <20190213133754.dae63726a93ba818e114cdb9@linux-foundation.org> In-Reply-To: <20190213124334.GH4525@dhcp22.suse.cz> References: <1549533189-9177-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20190212101109.GB7584@dhcp22.suse.cz> <82168e14-8a89-e6ac-1756-e473e9c21616@i-love.sakura.ne.jp> <20190212112117.GT15609@dhcp22.suse.cz> <20190212112954.GV15609@dhcp22.suse.cz> <20190212130620.c43e486c4f13c811e3d4a513@linux-foundation.org> <20190213124334.GH4525@dhcp22.suse.cz> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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, 13 Feb 2019 13:43:34 +0100 Michal Hocko wrote: > Since for_each_cpu(cpu, mask) added by commit 2d3854a37e8b767a ("cpumask: > introduce new API, without changing anything") did not evaluate the mask > argument if NR_CPUS == 1 due to CONFIG_SMP=n, lru_add_drain_all() is > hitting WARN_ON() at __flush_work() added by commit 4d43d395fed12463 > ("workqueue: Try to catch flush_work() without INIT_WORK().") > by unconditionally calling flush_work() [1]. > > Workaround this issue by using CONFIG_SMP=n specific lru_add_drain_all > implementation. There is no real need to defer the implementation to the > workqueue as the draining is going to happen on the local cpu. So alias > lru_add_drain_all to lru_add_drain which does all the necessary work. > I assume that warning comes out a LOT of times under the correct circumstances. Tejun, I think a WARN_ON_ONCE() would be better.