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[70.24.86.62]) by smtp.gmail.com with ESMTPSA id bw7-20020a05622a098700b003f6b32a1049sm1617002qtb.55.2023.05.26.15.42.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 May 2023 15:42:23 -0700 (PDT) Date: Fri, 26 May 2023 18:42:20 -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 03/31] mm/pgtable: kmap_local_page() instead of kmap_atomic() Message-ID: References: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> <9df4aba7-fd2f-2da3-1543-fc6b4b42f5b9@google.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: 93C0F100009 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 93yfxwqsgg518u8n6mtrqbzt1xs5wxps X-HE-Tag: 1685140946-641092 X-HE-Meta: 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 Philxwm4 EZ3TnKWmYDhuGC8nJe4oyQfq1pvHAPiTGNnLoX/mwZ3qQGh2Kfsqg9lMLkMbFpk9oEtYZbn9HNZEkkrF494IMfhLa97qRFsc4cq7fUrZtuj9CLYHXOVBdZESiozHI5IF32UTiz6HRQsfn7uYw3AxfgqLZXD8EiwYrCzWhdPt6WZE+Z7APhhxOSk0AWkgoi+Oq4BGsCth3TIB7vmBkTT2lucdeeqU70/CiFu/Q8DOb/yiRNJn7SvR5dR8TnddCaZxsZej5SYz+EwY+BUJtGGCTViPLOfNCFmLVMr1Z8py9As6h+xBBSHSI2ocB88zCTMlIKRB4LI0rjsc6HFumlukbJmQJZNS2PDAUvih+4FZEPKhSP3uYdsEVQ/8yLC7wnpb/d2CXZPZoNP0R+Jepa9XoyZJniSnQOMd0hm7w6hs9IFf9gJ6SdkTBN50sbw== 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, May 26, 2023 at 06:22:58PM -0400, Peter Xu wrote: > On Sun, May 21, 2023 at 09:52:31PM -0700, Hugh Dickins wrote: > > pte_offset_map() was still using kmap_atomic(): update it to the > > preferred kmap_local_page() before making further changes there, in case > > we need this as a bisection point; but I doubt it can cause any trouble. > > > > Signed-off-by: Hugh Dickins > > --- > > include/linux/pgtable.h | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > > index 8ec27fe69dc8..94235ff2706e 100644 > > --- a/include/linux/pgtable.h > > +++ b/include/linux/pgtable.h > > @@ -96,9 +96,9 @@ static inline pte_t *pte_offset_kernel(pmd_t *pmd, unsigned long address) > > > > #if defined(CONFIG_HIGHPTE) > > #define pte_offset_map(dir, address) \ > > - ((pte_t *)kmap_atomic(pmd_page(*(dir))) + \ > > + ((pte_t *)kmap_local_page(pmd_page(*(dir))) + \ > > pte_index((address))) > > -#define pte_unmap(pte) kunmap_atomic((pte)) > > +#define pte_unmap(pte) kunmap_local((pte)) > > #else > > #define pte_offset_map(dir, address) pte_offset_kernel((dir), (address)) > > #define pte_unmap(pte) ((void)(pte)) /* NOP */ > > (I think this could be a dumb question if this patch has been running there > for years downstream, but still..) > > I assume one major difference of using kmap_local() is page fault will not > be disabled, while kmap_atomic() will. > > Meanwhile, pte_offset_map() is also used by pte_offset_map_lock(), which > means before this patch CONFIG_HIGHPTE systems will disable pgfault before > taking pgtable lock for it, while it will stop doing so after the change. > > Then what happens if a page fault happens on the same pgtable lock range > that is already taken by the thread context? What stops the deadlock from > happening? Ah, stupid me. I think such a page fault just cannot happen when holding the pgtable lock.. I believe the same applies to !HIGHPTE.. Sorry about the noise. -- Peter Xu