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[70.24.86.62]) by smtp.gmail.com with ESMTPSA id a13-20020a05620a124d00b0075936b3026fsm1480280qkl.38.2023.05.26.15.22.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 May 2023 15:23:00 -0700 (PDT) Date: Fri, 26 May 2023 18:22:58 -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: <9df4aba7-fd2f-2da3-1543-fc6b4b42f5b9@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Stat-Signature: tmmtqscd4gkfms3iwmfodbq3emn9j5hb X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 60EAC1C0011 X-Rspam-User: X-HE-Tag: 1685139783-534388 X-HE-Meta: U2FsdGVkX1/jm8eRo1Yl8rYfO7HpCW0qMUtD9veR2ScfW//qldHOPK70IU8b2SYNolUHR5k9YNmb6jkwCLt2CDkFoGoMdekk/eaMTSyeHbMBW14YBdpDum2ZrPNN+wvj3dS/GTcagtBWPCVBxGRu18Qrtp4YyXvBPmQMEru8tTrkU2VtBhKJU18ixrKcR41HBI79Dhb3EM1N9mb8e/nk/HQvQoBNrDeWT6WOvRFwpJOEIHsbx8u03HgLdJxk1LTYHBu3SiYMXDlfmEvTVALkEduE/aBRx7Yv1O+ZAoEum5KJahyWRDIiF00k9xlZWUy0i16ye6Oq208TrGotuKwwL0U0KGS9f+m848oYz0rIZuo8IDHVZDG5qC6T2/2/moJHoQABT7PGdZAgYQwF2orirBPD5oZrNgUSMwpYwVieT4sRSH5ccSQcM+zE4tiUiCgVi35wEXNec6Udw+9Idr+nRYHYeLSNr1Zc7D5PoqcHxK6Z6uqRn/RMDNhIpExB6zVCyCLz2WKrS2/xWLS//W3OCz4kr8blJeARD/IYJ2NFcngnOgML9lg8Q8jHmbZmp4tf+zGYQczgpNCFR74WoeSzuCXf8gKc+httejuxJcETcq1JedoTm4O4JwvorA9KnXYBrGMR8h9WiE9alfxFElJ+u+3XMtMo+tjOkF2okNM4aijFRIyjQSzqje0ID9OVqXkFrdOzlZxKc2QIOyliSsr215ZdFhJtFe7UQhzzYmjBPkqIt+wH2tcLLkjA+UlJ+MBaJXFWEhDOOvPZCKweOHmwiWLZVSU12J3062JxzTlS7MJxNuReR1VgTg6yKVJ0QQG66iusY8xuqyx4Yt2QYfx+khWofpxVrGBFB/uVHejXSGEunOAEwmNc4PKJF/jqfsLANbaRjK6tjeEjv9njf+1+W0xoP3L3LT5+5R/L4as2MOFiXwAzUQxvZwjFdiw9lwncxa8G8UqDaRuPiHALQEz X/J6mQ9H hO1f8ijOmIuqLa1j5Vj2MfRZItoyG0bxgklfBtuGWGjJ0GEDngxnvdTY647sX5rtGF3kD2CV6quqX112YzNOSMCbMuIs5dul0US10m1DsxgERNQ9Q5I4H35vvZSDwFNOp1sdAvOd5jBzFi5y0tNu+uDGxPVgxoY/4TQk+wyMWyL3cXLa/7nEzeVaJcxMIx5fZveyHxkn2qZoDpt5EhuzUyI+Ooh1CT5FV5CIwnlqUDvfafu+k//P/QxQVzryyTOuFVYnM5vQWrEawVq992rIkeUMZLyuCrdvGdnFJs8ECJ6PWsU1JXsb5QvIxclN91X0Kt7PflBb/tIHj+TyGHIB2ds4sP+7oOI0xnHybslsMEcpP9wx4HeJ1cc/HLewIGXsp2swogbdWYM9JHBJBs1/ui5dcB9QxDv0zOyyEhqXIexWbhyEvSdOwjXS/Kw== 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 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? Thanks, -- Peter Xu