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Tue, 04 Jan 2022 03:49:43 -0800 (PST) MIME-Version: 1.0 References: <20211211022115.1547617-1-mfo@canonical.com> <871r2ct207.fsf@yhuang6-desk2.ccr.corp.intel.com> In-Reply-To: <871r2ct207.fsf@yhuang6-desk2.ccr.corp.intel.com> From: Mauricio Faria de Oliveira Date: Tue, 4 Jan 2022 08:49:32 -0300 Message-ID: Subject: Re: [PATCH] mm: fix race between MADV_FREE reclaim and blkdev direct IO read To: "Huang, Ying" Cc: Minchan Kim , Andrew Morton , linux-mm@kvack.org, linux-block@vger.kernel.org, Miaohe Lin Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: D2E6140002 X-Stat-Signature: s4c5ofwpbxry94n78j9isrz45it5ktaa Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=canonical.com header.s=20210705 header.b=LZ8iaik6; spf=pass (imf07.hostedemail.com: domain of mauricio.oliveira@canonical.com designates 185.125.188.122 as permitted sender) smtp.mailfrom=mauricio.oliveira@canonical.com; dmarc=pass (policy=none) header.from=canonical.com X-HE-Tag: 1641296986-395049 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, Dec 16, 2021 at 11:10 PM Huang, Ying wrote: > > Minchan Kim writes: ... > > > > A madv_free marked page could be mapped at several processes so > > it wouldn't be refcount two all the time, I think. > > Shouldn't we check it with page_mapcount with page_refcount? > > > > page_ref_count(page) - 1 > page_mapcount(page) > > > > And should we consider page_count() too in madvise_free_pte_range()? > That is, if the page has been used by GUP, we needn't to make its PTE > clean? Hey, thanks for reviewing! That might not be sufficient time-wise, I guess, because the page can be used by GUP after the madvise() call (e.g., this case), thus checking for it during the call wouldn't catch it -- this may apply to other cases too, where there's no guarantee/ordering between both operations. cheers, -- Mauricio Faria de Oliveira