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Fri, 04 Jun 2021 21:20:06 -0700 (PDT) MIME-Version: 1.0 References: <20210524132725.12697-1-apopple@nvidia.com> <20210524132725.12697-4-apopple@nvidia.com> <20210525183710.fa2m2sbfixnhz7g5@revolver> <20210604204934.sbspsmwdqdtmz73d@revolver> <20210605033926.pkeq2saomieebrqa@revolver> In-Reply-To: <20210605033926.pkeq2saomieebrqa@revolver> From: Shakeel Butt Date: Fri, 4 Jun 2021 21:19:55 -0700 Message-ID: Subject: Re: [PATCH v9 03/10] mm/rmap: Split try_to_munlock from try_to_unmap To: Liam Howlett Cc: Alistair Popple , "linux-mm@kvack.org" , "akpm@linux-foundation.org" , "nouveau@lists.freedesktop.org" , "bskeggs@redhat.com" , "rcampbell@nvidia.com" , "linux-doc@vger.kernel.org" , "jhubbard@nvidia.com" , "bsingharora@gmail.com" , "linux-kernel@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "hch@infradead.org" , "jglisse@redhat.com" , "willy@infradead.org" , "jgg@nvidia.com" , "peterx@redhat.com" , "hughd@google.com" , Christoph Hellwig Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=hMgR5HN4; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf29.hostedemail.com: domain of shakeelb@google.com designates 209.85.208.170 as permitted sender) smtp.mailfrom=shakeelb@google.com X-Stat-Signature: xoygqf1o6rjse87wn5ce3mga3zmotpzh X-Rspamd-Queue-Id: 6FD422701 X-Rspamd-Server: rspam02 X-HE-Tag: 1622874195-758161 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 Fri, Jun 4, 2021 at 8:39 PM Liam Howlett wrote: > > > Particularly the following paragraph: > > ... > > Vlastimil Babka points out another race which this patch protects against. > > try_to_unmap_one() might reach its mlock_vma_page() TestSetPageMlocked a > > moment after munlock_vma_pages_all() did its Phase 1 TestClearPageMlocked: > > leaving PageMlocked and unevictable when it should be evictable. mmap_sem > > is ineffective because exit_mmap() does not hold it; page lock ineffective > > because __munlock_pagevec() only takes it afterwards, in Phase 2; pte lock > > is effective because __munlock_pagevec_fill() takes it to get the page, > > after VM_LOCKED was cleared from vm_flags, so visible to try_to_unmap_one. > > ... > > So this is saying the race with exit_mmap() isn't benign after all? > Yes, not benign at all.