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Shutemov" To: Linus Torvalds Cc: Hugh Dickins , Matthew Wilcox , Linux-MM , Andrew Morton , linux-fsdevel , Amir Goldstein Subject: Re: [PATCH 0/4] Some more lock_page work.. Message-ID: <20201014130555.kdbxyavqoyfnpos3@box> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000614, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Oct 13, 2020 at 01:03:30PM -0700, Linus Torvalds wrote: > On Tue, Oct 13, 2020 at 12:59 PM Linus Torvalds > wrote: > > > > Comments? So we remove strict serialization against truncation in filemap_map_pages() if the mapping is private. IIUC, we can end up with a page with ->mapping == NULL set up in a PTE for such mappings. The "page->mapping != mapping" check makes the race window smaller, but doesn't remove it. I'm not sure all codepaths are fine with this. For instance, looks like migration will back off such pages: __unmap_and_move() doesn't know how to deal with mapped pages with ->mapping == NULL. Yes, it is not crash, but still... Do I miss something? -- Kirill A. Shutemov