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[70.27.3.10]) by smtp.gmail.com with ESMTPSA id bk4-20020a05620a1a0400b006b89a19a32dsm3074109qkb.69.2022.08.05.08.52.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Aug 2022 08:52:19 -0700 (PDT) Date: Fri, 5 Aug 2022 11:52:18 -0400 From: Peter Xu To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Yang Shi , Nadav Amit , David Hildenbrand , Konstantin Khlebnikov Subject: Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent Message-ID: References: <20220803220329.46299-1-peterx@redhat.com> <20220804154050.e6ab9f8c38e2445acc5b57b1@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20220804154050.e6ab9f8c38e2445acc5b57b1@linux-foundation.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 04, 2022 at 03:40:50PM -0700, Andrew Morton wrote: > On Wed, 3 Aug 2022 18:03:29 -0400 Peter Xu wrote: > > > These bits should only be valid when the ptes are present. Introducing two > > booleans for it and set it to false when !pte_present(). > > Please (always) describe the user visible runtime effects of the bug > which is being fixed? Will do in the future. For this specific one I'll add some more details: The bug is found during code reading and no real world issue reported, but logically such an error can cause incorrect readings for either smaps or smaps_rollup output on quite a few fields. For example, it could cause over-estimate on values like Shared_Dirty, Private_Dirty, Referenced; or it could also cause under-estimate on values like LazyFree, Shared_Clean, Private_Clean. Meanwhile I think I overlooked the pmd handling which seems to have the same issue but done in another commit.. Will repost soon. Thanks, > > > > --- a/fs/proc/task_mmu.c > > +++ b/fs/proc/task_mmu.c > > @@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr, > > struct vm_area_struct *vma = walk->vma; > > bool locked = !!(vma->vm_flags & VM_LOCKED); > > struct page *page = NULL; > > - bool migration = false; > > + bool migration = false, young = false, dirty = false; > > > > if (pte_present(*pte)) { > > page = vm_normal_page(vma, addr, *pte); > > + young = pte_young(*pte); > > + dirty = pte_dirty(*pte); > > } else if (is_swap_pte(*pte)) { > > swp_entry_t swpent = pte_to_swp_entry(*pte); > > > > @@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr, > > if (!page) > > return; > > > > - smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte), > > - locked, migration); > > + smaps_account(mss, page, false, young, dirty, locked, migration); > > } > > > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > > -- > > 2.32.0 > -- Peter Xu