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[195.135.220.15]) by mx.google.com with ESMTPS id q29si11782469eda.83.2019.07.26.00.57.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 Jul 2019 00:57:30 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id A6042B01F; Fri, 26 Jul 2019 07:57:29 +0000 (UTC) Date: Fri, 26 Jul 2019 09:57:29 +0200 From: Michal Hocko To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-acpi@vger.kernel.org, "Rafael J. Wysocki" , Andrew Morton , Oscar Salvador Subject: Re: [PATCH v1] ACPI / scan: Acquire device_hotplug_lock in acpi_scan_init() Message-ID: <20190726075729.GG6142@dhcp22.suse.cz> References: <20190724143017.12841-1-david@redhat.com> <20190725125636.GA3582@dhcp22.suse.cz> <6dc566c2-faf6-565d-4ef1-2ac3a366bc76@redhat.com> <20190725135747.GB3582@dhcp22.suse.cz> <447b74ca-f7c7-0835-fd50-a9f7191fe47c@redhat.com> <20190725191943.GA6142@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) 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 Thu 25-07-19 22:49:36, David Hildenbrand wrote: > On 25.07.19 21:19, Michal Hocko wrote: [...] > > We need to rationalize the locking here, not to add more hacks. > > No, sorry. The real hack is calling a function that is *documented* to > be called under lock without it. That is an optimization for a special > case. That is the black magic in the code. OK, let me ask differently. What does the device_hotplug_lock actually protects from in the add_memory path? (Which data structures) This function is meant to be used when struct pages and node/zone data structures should be updated. Why should we even care about some device concept here? This should all be handled a layer up. Not all memory will have user space API to control online/offline state. -- Michal Hocko SUSE Labs