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Shutemov" Cc: Jann Horn , Andrew Morton , linux-mm@kvack.org, "Kirill A. Shutemov" , "Zach O'Keefe" , linux-kernel@vger.kernel.org, David Hildenbrand Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 0C9ED180002 X-Stat-Signature: bb7s744i1zf7477kqx1mgojmpdw93si5 X-HE-Tag: 1673580178-110680 X-HE-Meta: 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 q7NpDMmA FLMljGpA+Q6CCDkOdLf1ZbdEi9EC8Sn4ahhQHDlRgT2fIvXXffrDEKM/DxL3+XOr4tOIWu3Sq6gDSt/+Fiks8Fg+w1mLCLXUOGm0n X-Bogosity: Ham, tests=bogofilter, spamicity=0.000016, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jan 12, 2023 at 4:10 PM Kirill A. Shutemov wrote: > > On Thu, Jan 12, 2023 at 10:12:53AM -0800, Yang Shi wrote: > > > This is totally wrong direction. Or I don't understand the race. > > > > > > At this point we already paid nearly all price of of pagetable retraction. > > > I don't see any correctness reason to stop here, except for the assert. > > > > Isn't it possible that collapse_and_free_pmd() clear the pmd which may > > point to a PTE which maps the COW'ed anon page if this race happens? > > No. At this point we have huge page in the place in the page cache and it > is locked. COW fault would serialize on the page lock. Aha, yeah, I missed the page lock. So IIUC even though anon_vma is set there should be not any COW'ed anon pages since cow fault would be blocked by the page lock. If so I tend to agree with you the lockdep assert seems unnecessary. > > -- > Kiryl Shutsemau / Kirill A. Shutemov