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Mon, 15 Sep 2025 03:48:11 -0700 (PDT) Received: from localhost ([196.207.164.177]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-3e7607cd6absm17408269f8f.34.2025.09.15.03.48.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Sep 2025 03:48:10 -0700 (PDT) Date: Mon, 15 Sep 2025 13:48:07 +0300 From: Dan Carpenter To: Balbir Singh Cc: linux-mm@kvack.org Subject: Re: [bug report] lib/test_hmm: add zone device private THP test infrastructure Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: E15C04000C X-Stat-Signature: ut4z6d5icykaihjfico3emeny67wzace X-Rspam-User: X-HE-Tag: 1757933292-299626 X-HE-Meta: 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 lzA8NdS4 T6iVfgfoabEJCjd13jlqsk2fROS8WoSdtYaYveToIbhdc91IiZV9gTocBtkWu6Hx3cdTs47kmNOo02OzShXircx/UXQZVbeaSyGni+vvFhTHAfwinImx/xDDfovQC7ONXjVAwRyOmDdnlxaK+4bKK/KJRnyraXdOeveW1RDO3sgFQqMe0tCE3R2wg83Oov1SoFw5DYY80s6mROHBbjq7xEUTuy+IF/Xx6uWg7lP8j2XStXVLd+t7n0tcTtvsum+xlGcD7D5vXNo8uyvo0y04rMNMc51cNKpYdhHgBJctXOYFyu6tqeE9EDvPqrtpYtEPTBz4P 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: List-Subscribe: List-Unsubscribe: On Mon, Sep 15, 2025 at 07:49:33PM +1000, Balbir Singh wrote: > On 9/15/25 15:50, Dan Carpenter wrote: > > Hello Balbir Singh, > > > > Commit 6098c878b175 ("lib/test_hmm: add zone device private THP test > > infrastructure") from Sep 8, 2025 (linux-next), leads to the > > following Smatch static checker warning: > > > > lib/test_hmm.c:721 dmirror_migrate_alloc_and_copy() > > error: we previously assumed 'spage' could be null (see line 718) > > > > lib/test_hmm.c > > 675 static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args, > > 676 struct dmirror *dmirror) > > 677 { > > 678 const unsigned long *src = args->src; > > 679 unsigned long *dst = args->dst; > > 680 unsigned long addr; > > 681 > > 682 for (addr = args->start; addr < args->end; ) { > > 683 struct page *spage; > > 684 struct page *dpage; > > 685 struct page *rpage; > > 686 bool is_large = *src & MIGRATE_PFN_COMPOUND; > > 687 int write = (*src & MIGRATE_PFN_WRITE) ? MIGRATE_PFN_WRITE : 0; > > 688 unsigned long nr = 1; > > 689 > > 690 if (!(*src & MIGRATE_PFN_MIGRATE)) > > 691 goto next; > > 692 > > 693 /* > > 694 * Note that spage might be NULL which is OK since it is an > > 695 * unallocated pte_none() or read-only zero page. > > 696 */ > > 697 spage = migrate_pfn_to_page(*src); > > 698 if (WARN(spage && is_zone_device_page(spage), > > 699 "page already in device spage pfn: 0x%lx\n", > > 700 page_to_pfn(spage))) > > 701 goto next; > > 702 > > 703 if (dmirror->flags & HMM_DMIRROR_FLAG_FAIL_ALLOC) { > > 704 dmirror->flags &= ~HMM_DMIRROR_FLAG_FAIL_ALLOC; > > 705 dpage = NULL; > > 706 } else > > 707 dpage = dmirror_devmem_alloc_page(dmirror, is_large); > > 708 > > 709 if (!dpage) { > > 710 struct folio *folio; > > 711 unsigned long i; > > 712 unsigned long spfn = *src >> MIGRATE_PFN_SHIFT; > > 713 struct page *src_page; > > 714 > > 715 if (!is_large) > > 716 goto next; > > 717 > > 718 if (!spage && is_large) { > > ^^^^^^ ^^^^^^^^ > > If spage is NULL but is_large is false > > Isn't is_large being false ruled out two lines above? > Ah, yes. When Smatch sees an impossible condition like that, the assumption is that probably the static checker has messed up. So there isn't special code to filter out impossible conditions. For some Smatch checks like the uninitialized variable warning, then warnings in dead code are filtered out. But the line with the warning is not dead code so it's more complicated. regards, dan carpenter > > > > 719 nr = HPAGE_PMD_NR; > > 720 } else { > > --> 721 folio = page_folio(spage); > > ^^^^^ > > the this will crash. > > > > 722 nr = folio_nr_pages(folio); > > 723 } > > 724 > > 725 for (i = 0; i < nr && addr < args->end; i++) { > > > > regards, > > dan carpenter > > Thanks, > Balbir