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Tue, 28 May 2024 07:47:56 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id fVzvKyyMVWZgQQAAD6G6ig (envelope-from ); Tue, 28 May 2024 07:47:56 +0000 Date: Tue, 28 May 2024 09:47:47 +0200 From: Oscar Salvador To: David Hildenbrand Cc: kernel test robot , Matthew Wilcox , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Andrew Morton , Vlastimil Babka , Luis Chamberlain , Miaohe Lin , Muchun Song , linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: Re: [linus:master] [mm] d99e3140a4: BUG:KCSAN:data-race_in_folio_remove_rmap_ptes/print_report Message-ID: References: <202405281431.c46a3be9-lkp@intel.com> <8aba80ed-7b3e-4c8c-99e8-d8a2e0b112fc@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8aba80ed-7b3e-4c8c-99e8-d8a2e0b112fc@redhat.com> X-Rspamd-Queue-Id: 3BAA880011 X-Stat-Signature: np8jy87i95fr5aumt6kbme83eegsejfj X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1716882478-412385 X-HE-Meta: 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 goFNhxQW KzVOLltHBui8KVUw3up0Gphd9ptQIeVt6EGnsJZAEO6pAb5HjhdaSX2uAOK0Mq1FWJGvGka0b/+uA7N1J2eBgM6kR+TqolT4FS9E1PQ00wyukcWqjKhvryak4jQHH9f79ncUSteeiHhX/2Wf9s998tFss7d/mDetAMpgB/iL1KdZlbXY1tCD3H2AdQFQ9d6UvRpbRd5wtPjY3T4egjpNP4Zd2XKnzTYXTJWfCq8W2VllEpSUavxhqcdENDt2gezOkzLKDyzLS3PvRC27+vTel7wqgTG1BjcUKPc6sYH4rQ6f9y0xhFt9lamkaLNlWqaYR1GVDgKRPMPkGxVRnADhghBXNqK0BFIvC79j9stmy29zl+EQ= 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 Tue, May 28, 2024 at 09:43:39AM +0200, David Hildenbrand wrote: > Likely that's just a page_type check racing against concurrent > mapcount changes. > > In __folio_rmap_sanity_checks() we check > VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio); Yeah, and that "collides" with last = atomic_add_negative(-1, &page->_mapcount) from __folio_remove_rmap. > To make sure we don't get hugetlb folios in the wrong rmap code path. That > can easily race with concurrent mapcount changes, just like any other > page_type checks that end up in folio_test_type/page_has_type e.g., from > PFN walkers. > > Load tearing in these functions shouldn't really result in false positives > (what we care about), but READ_ONCE shouldn't hurt or make a difference. > > > From b03dc9bf27571442d886d8da624a4e4f737433f2 Mon Sep 17 00:00:00 2001 > From: David Hildenbrand > Date: Tue, 28 May 2024 09:37:20 +0200 > Subject: [PATCH] mm: read page_type using READ_ONCE > > KCSAN complains about possible data races: while we check for a > page_type -- for example for sanity checks -- we might concurrently > modify the mapcount that overlays page_type. > > Let's use READ_ONCE to avoid laod tearing (shouldn't make a difference) > and to make KCSAN happy. > > Note: nothing should really be broken besides wrong KCSAN complaints. > > Reported-by: kernel test robot > Closes: https://lore.kernel.org/oe-lkp/202405281431.c46a3be9-lkp@intel.com > Signed-off-by: David Hildenbrand Reviewed-by: Oscar Salvador Thanks! -- Oscar Salvador SUSE Labs