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Wed, 27 Mar 2024 08:23:55 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFT3GjlhPAIM0f0tWP3PNax9bFYBunh5winrPqMP8FazkZOSJ/P00xdKeX4lX2Up3S+10Z8OQ== X-Received: by 2002:a05:6214:3d8c:b0:696:1892:c19f with SMTP id om12-20020a0562143d8c00b006961892c19fmr15035509qvb.3.1711553034516; Wed, 27 Mar 2024 08:23:54 -0700 (PDT) Received: from x1n.redhat.com ([99.254.121.117]) by smtp.gmail.com with ESMTPSA id hu4-20020a056214234400b00690dd47a41csm6412639qvb.86.2024.03.27.08.23.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Mar 2024 08:23:54 -0700 (PDT) From: peterx@redhat.com To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 09/13] mm/gup: Cache *pudp in follow_pud_mask() Date: Wed, 27 Mar 2024 11:23:28 -0400 Message-ID: <20240327152332.950956-10-peterx@redhat.com> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240327152332.950956-1-peterx@redhat.com> References: <20240327152332.950956-1-peterx@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: James Houghton , David Hildenbrand , Yang Shi , peterx@redhat.com, Andrew Jones , linux-riscv@lists.infradead.org, Andrea Arcangeli , Christoph Hellwig , Matthew Wilcox , "Aneesh Kumar K . V" , linux-arm-kernel@lists.infradead.org, Jason Gunthorpe , Axel Rasmussen , Rik van Riel , John Hubbard , "Kirill A . Shutemov" , Vlastimil Babka , Lorenzo Stoakes , Muchun Song , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Mike Rapoport , Mike Kravetz Errors-To: linuxppc-dev-bounces+incoming=patchwork.ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" From: Peter Xu Introduce "pud_t pud" in the function, so the code won't dereference *pudp multiple time. Not only because that looks less straightforward, but also because if the dereference really happened, it's not clear whether there can be race to see different *pudp values if it's being modified at the same time. Acked-by: James Houghton Reviewed-by: Jason Gunthorpe Signed-off-by: Peter Xu --- mm/gup.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index ef46a7053e16..26b8cca24077 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -753,26 +753,27 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma, unsigned int flags, struct follow_page_context *ctx) { - pud_t *pud; + pud_t *pudp, pud; spinlock_t *ptl; struct page *page; struct mm_struct *mm = vma->vm_mm; - pud = pud_offset(p4dp, address); - if (pud_none(*pud)) + pudp = pud_offset(p4dp, address); + pud = READ_ONCE(*pudp); + if (pud_none(pud)) return no_page_table(vma, flags, address); - if (pud_devmap(*pud)) { - ptl = pud_lock(mm, pud); - page = follow_devmap_pud(vma, address, pud, flags, &ctx->pgmap); + if (pud_devmap(pud)) { + ptl = pud_lock(mm, pudp); + page = follow_devmap_pud(vma, address, pudp, flags, &ctx->pgmap); spin_unlock(ptl); if (page) return page; return no_page_table(vma, flags, address); } - if (unlikely(pud_bad(*pud))) + if (unlikely(pud_bad(pud))) return no_page_table(vma, flags, address); - return follow_pmd_mask(vma, address, pud, flags, ctx); + return follow_pmd_mask(vma, address, pudp, flags, ctx); } static struct page *follow_p4d_mask(struct vm_area_struct *vma,