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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id x3sm5516825qkl.107.2021.09.23.20.59.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Sep 2021 20:59:02 -0700 (PDT) Date: Thu, 23 Sep 2021 20:59:00 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.anvils To: Peter Xu cc: linux-kernel@vger.kernel.org, Andrew Morton , linux-mm@kvack.org, Hugh Dickins , David Hildenbrand , Liam Howlett , Mike Rapoport , Alistair Popple , Matthew Wilcox , Yang Shi , "Kirill A . Shutemov" , Jerome Glisse , Miaohe Lin , Andrea Arcangeli Subject: Re: [PATCH v4 2/4] mm: Clear vmf->pte after pte_unmap_same() returns In-Reply-To: <20210915181533.11188-1-peterx@redhat.com> Message-ID: <7b877ef5-9dd5-97ed-dd1a-36dbf5d02547@google.com> References: <20210915181456.10739-1-peterx@redhat.com> <20210915181533.11188-1-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C9C0DD501FC7 X-Stat-Signature: d4gnehjsi4iuxrfdfyfehcak1n4w91ch Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=laalLWc0; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf21.hostedemail.com: domain of hughd@google.com designates 209.85.160.170 as permitted sender) smtp.mailfrom=hughd@google.com X-HE-Tag: 1632455943-619662 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 Wed, 15 Sep 2021, Peter Xu wrote: > pte_unmap_same() will always unmap the pte pointer. After the unmap, vmf->pte > will not be valid any more, we should clear it. > > It was safe only because no one is accessing vmf->pte after pte_unmap_same() > returns, since the only caller of pte_unmap_same() (so far) is do_swap_page(), > where vmf->pte will in most cases be overwritten very soon. > > Directly pass in vmf into pte_unmap_same() and then we can also avoid the long > parameter list too, which should be a nice cleanup. > > Reviewed-by: Miaohe Lin > Reviewed-by: David Hildenbrand > Reviewed-by: Liam Howlett > Signed-off-by: Peter Xu This one seems fine, thanks. Acked-by: Hugh Dickins > --- > mm/memory.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 25fc46e87214..7b095f07c4ef 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2724,19 +2724,19 @@ EXPORT_SYMBOL_GPL(apply_to_existing_page_range); > * proceeding (but do_wp_page is only called after already making such a check; > * and do_anonymous_page can safely check later on). > */ > -static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd, > - pte_t *page_table, pte_t orig_pte) > +static inline int pte_unmap_same(struct vm_fault *vmf) > { > int same = 1; > #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPTION) > if (sizeof(pte_t) > sizeof(unsigned long)) { > - spinlock_t *ptl = pte_lockptr(mm, pmd); > + spinlock_t *ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd); > spin_lock(ptl); > - same = pte_same(*page_table, orig_pte); > + same = pte_same(*vmf->pte, vmf->orig_pte); > spin_unlock(ptl); > } > #endif > - pte_unmap(page_table); > + pte_unmap(vmf->pte); > + vmf->pte = NULL; > return same; > } > > @@ -3487,7 +3487,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > vm_fault_t ret = 0; > void *shadow = NULL; > > - if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte)) > + if (!pte_unmap_same(vmf)) > goto out; > > entry = pte_to_swp_entry(vmf->orig_pte); > -- > 2.31.1