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[70.24.86.62]) by smtp.gmail.com with ESMTPSA id t7-20020a05622a01c700b003f6ac526568sm3112027qtw.39.2023.05.24.15.31.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 May 2023 15:31:20 -0700 (PDT) Date: Wed, 24 May 2023 18:31:18 -0400 From: Peter Xu To: Hugh Dickins Cc: Andrew Morton , Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 14/31] fs/userfaultfd: retry if pte_offset_map() fails Message-ID: References: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> <424274a4-7c13-e14-b380-428fc69a45c5@google.com> MIME-Version: 1.0 In-Reply-To: <424274a4-7c13-e14-b380-428fc69a45c5@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 9E96A180017 X-Stat-Signature: uehxp1rryreuhibchhmyp8baaq43ebgs X-HE-Tag: 1684967483-160390 X-HE-Meta: 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 oX71mFIC lsyhJ2RQzZpHCfdXFvEC2o1xa1VBPF8TkbY9OWE4qiZdCAhOiTXy/GrCMIzwlIAXJBGo08QRLw/jsfPWgHcLVu+m62QE7wELsukDhI6VYF0mR5Mfs7sJZ1GwxLgdjh/yeN+YQY/N10Wj/OI1+oKz5v9+njrCTJkGY+A98utsTsuVskorLJD3qFCp7AD4TDfs1oyJqITy4bMT58yLpyyUIAjP9PgMhVcL8a3l1df3zt8Tk60DraXqrvzQNXvFR5BCMRzw5GBl2+oeoQOj5ChzG1fh2kx2jhofsghp4oPXYAnR0aKwM9OkozjDPhyQJt0JpDsK3HNtd5pNe9b2NU0JGQdU301hAVnztOUk4vVWmQrsAz2wVYP+vzQmNFC6gJjTnKp7wcgw5ZN3yEt514rrYjsfMY0+2tITgv2+kv0Du+02v83Qpxb48FS2K3GmgEux20282njtn980K7mZCspZIgm7xFfcugF2yrr31 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 Sun, May 21, 2023 at 10:06:32PM -0700, Hugh Dickins wrote: > Instead of worrying whether the pmd is stable, userfaultfd_must_wait() > call pte_offset_map() as before, but go back to try again if that fails. > > Risk of endless loop? It already broke out if pmd_none(), !pmd_present() > or pmd_trans_huge(), and pte_offset_map() would have cleared pmd_bad(): > which leaves pmd_devmap(). Presumably pmd_devmap() is inappropriate in > a vma subject to userfaultfd (it would have been mistreated before), > but add a check just to avoid all possibility of endless loop there. Agreed, afaiu that's for either PFNMAP or MIXEDMAP vmas only. Maybe we can use a WARN_ON_ONCE() for that to be clear, but no strong opinions. > > Signed-off-by: Hugh Dickins Acked-by: Peter Xu -- Peter Xu