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Shutemov" To: John Hubbard Cc: Andrew Morton , Al Viro , Christoph Hellwig , Dan Williams , Dave Chinner , Ira Weiny , Jan Kara , Jason Gunthorpe , Jonathan Corbet , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Michal Hocko , Mike Kravetz , Shuah Khan , Vlastimil Babka , Matthew Wilcox , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-rdma@vger.kernel.org, linux-mm@kvack.org, LKML , "Kirill A . Shutemov" Subject: Re: [PATCH v3 07/12] mm/gup: track FOLL_PIN pages Message-ID: <20200203134024.htczuqghduajb3yx@box> References: <20200201034029.4063170-1-jhubbard@nvidia.com> <20200201034029.4063170-8-jhubbard@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200201034029.4063170-8-jhubbard@nvidia.com> Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Fri, Jan 31, 2020 at 07:40:24PM -0800, John Hubbard wrote: > @@ -4405,7 +4392,13 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, > same_page: > if (pages) { > pages[i] = mem_map_offset(page, pfn_offset); > - get_page(pages[i]); > + if (!try_grab_page(pages[i], flags)) { > + spin_unlock(ptl); > + remainder = 0; > + err = -ENOMEM; > + WARN_ON_ONCE(1); The WARN_ON_ONCE deserve a comment. And I guess you can put it into 'if' condition. > + break; > + } > } > > if (vmas) > @@ -4965,6 +4958,12 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, > struct page *page = NULL; > spinlock_t *ptl; > pte_t pte; > + > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == > + (FOLL_PIN | FOLL_GET))) > + return NULL; > + > retry: > ptl = pmd_lockptr(mm, pmd); > spin_lock(ptl); > @@ -4977,8 +4976,11 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, > pte = huge_ptep_get((pte_t *)pmd); > if (pte_present(pte)) { > page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT); > - if (flags & FOLL_GET) > - get_page(page); > + if (unlikely(!try_grab_page(page, flags))) { > + WARN_ON_ONCE(1); Ditto. > + page = NULL; > + goto out; > + } > } else { > if (is_hugetlb_entry_migration(pte)) { > spin_unlock(ptl); -- Kirill A. Shutemov