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[217.140.110.172]) by mx.google.com with ESMTP id h45si2733690edh.35.2019.06.13.08.21.03 for ; Thu, 13 Jun 2019 08:21:03 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) client-ip=217.140.110.172; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 77F3B367; Thu, 13 Jun 2019 08:21:02 -0700 (PDT) Received: from [10.162.40.191] (p8cg001049571a15.blr.arm.com [10.162.40.191]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 15B0F3F718; Thu, 13 Jun 2019 08:20:58 -0700 (PDT) Subject: Re: [PATCH] mm/vmalloc: Check absolute error return from vmap_[p4d|pud|pmd|pte]_range() To: Roman Penyaev Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Rick Edgecombe , Andrey Ryabinin , Mike Rapoport , Roman Gushchin , Michal Hocko , "Uladzislau Rezki (Sony)" , Andrew Morton References: <1560413551-17460-1-git-send-email-anshuman.khandual@arm.com> <7cc6a46c50c2008bfb968c5e48af5a49@suse.de> From: Anshuman Khandual Message-ID: <406afc57-5a77-a77c-7f71-df1e6837dae1@arm.com> Date: Thu, 13 Jun 2019 20:51:17 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <7cc6a46c50c2008bfb968c5e48af5a49@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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 06/13/2019 03:03 PM, Roman Penyaev wrote: > On 2019-06-13 10:12, Anshuman Khandual wrote: >> vmap_pte_range() returns an -EBUSY when it encounters a non-empty PTE. But >> currently vmap_pmd_range() unifies both -EBUSY and -ENOMEM return code as >> -ENOMEM and send it up the call chain which is wrong. Interestingly enough >> vmap_page_range_noflush() tests for the absolute error return value from >> vmap_p4d_range() but it does not help because -EBUSY has been merged with >> -ENOMEM. So all it can return is -ENOMEM. Fix this by testing for absolute >> error return from vmap_pmd_range() all the way up to vmap_p4d_range(). > > I could not find any real external caller of vmap API who really cares > about the errno, and frankly why they should?  This is allocation path, map_vm_area() which is an exported symbol suppose to provide the right error code regardless whether it's current users care for it or not. > allocation failed - game over.  When you step on -EBUSY case something > has gone completely wrong in your kernel, you get a big warning in > your dmesg and it is already does not matter what errno you get. Its true that vmap_pte_range() does warn during error conditions. But if we really dont care about error return code then we should just remove specific error details (ENOMEM/EBUSY) and instead replace them with simple boolean false/true or (0/1/-1) return values at each level. Will that be acceptable ? What we have currently is wrong where vmap_pmd_range() could just wrap EBUSY as ENOMEM and send up the call chain.