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[2003:cb:c703:7600:a8ea:29ce:7ee3:dd41]) by smtp.gmail.com with ESMTPSA id u11-20020a5d6acb000000b00241c4bd6c09sm2060024wrw.33.2022.11.30.08.39.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Nov 2022 08:39:51 -0800 (PST) Message-ID: <8290e578-9eaa-5859-6309-e62634b66fb5@redhat.com> Date: Wed, 30 Nov 2022 17:39:50 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Subject: Re: [PATCH 09/10] mm/hugetlb: Make page_vma_mapped_walk() safe to pmd unshare Content-Language: en-US To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, James Houghton , Jann Horn , Andrew Morton , Andrea Arcangeli , Rik van Riel , Nadav Amit , Miaohe Lin , Muchun Song , Mike Kravetz References: <20221129193526.3588187-1-peterx@redhat.com> <20221129193526.3588187-10-peterx@redhat.com> <65a3a912-3534-6718-2c55-e0d4b5246f1e@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30.11.22 17:32, Peter Xu wrote: > On Wed, Nov 30, 2022 at 05:18:45PM +0100, David Hildenbrand wrote: >> On 29.11.22 20:35, Peter Xu wrote: >>> Since page_vma_mapped_walk() walks the pgtable, it needs the vma lock >>> to make sure the pgtable page will not be freed concurrently. >>> >>> Signed-off-by: Peter Xu >>> --- >>> include/linux/rmap.h | 4 ++++ >>> mm/page_vma_mapped.c | 5 ++++- >>> 2 files changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >>> index bd3504d11b15..a50d18bb86aa 100644 >>> --- a/include/linux/rmap.h >>> +++ b/include/linux/rmap.h >>> @@ -13,6 +13,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> /* >>> * The anon_vma heads a list of private "related" vmas, to scan if >>> @@ -408,6 +409,9 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw) >>> pte_unmap(pvmw->pte); >>> if (pvmw->ptl) >>> spin_unlock(pvmw->ptl); >>> + /* This needs to be after unlock of the spinlock */ >>> + if (is_vm_hugetlb_page(pvmw->vma)) >>> + hugetlb_vma_unlock_read(pvmw->vma); >>> } >>> bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw); >>> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >>> index 93e13fc17d3c..f94ec78b54ff 100644 >>> --- a/mm/page_vma_mapped.c >>> +++ b/mm/page_vma_mapped.c >>> @@ -169,10 +169,13 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) >>> if (pvmw->pte) >>> return not_found(pvmw); >>> + hugetlb_vma_lock_read(vma); >>> /* when pud is not present, pte will be NULL */ >>> pvmw->pte = huge_pte_offset(mm, pvmw->address, size); >>> - if (!pvmw->pte) >>> + if (!pvmw->pte) { >>> + hugetlb_vma_unlock_read(vma); >>> return false; >>> + } >>> pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte); >>> if (!check_pte(pvmw)) >> >> Looking at code like mm/damon/paddr.c:__damon_pa_mkold() and reading the >> doc of page_vma_mapped_walk(), this might be broken. >> >> Can't we get page_vma_mapped_walk() called multiple times? > > Yes it normally can, but not for hugetlbfs? Feel free to check: > > if (unlikely(is_vm_hugetlb_page(vma))) { > ... > /* The only possible mapping was handled on last iteration */ > if (pvmw->pte) > return not_found(pvmw); > } Ah, I see, thanks. Acked-by: David Hildenbrand -- Thanks, David / dhildenb