From c403f6a3a792a6601185497c12b0bdf4be880439 Mon Sep 17 00:00:00 2001 From: Qian Cai Date: Fri, 14 Aug 2020 17:31:53 -0700 Subject: [PATCH] mm: annotate a data race in page_zonenum() BUG: KCSAN: data-race in page_cpupid_xchg_last / put_page write (marked) to 0xfffffc0d48ec1a00 of 8 bytes by task 91442 on cpu 3: page_cpupid_xchg_last+0x51/0x80 page_cpupid_xchg_last at mm/mmzone.c:109 (discriminator 11) wp_page_reuse+0x3e/0xc0 wp_page_reuse at mm/memory.c:2453 do_wp_page+0x472/0x7b0 do_wp_page at mm/memory.c:2798 __handle_mm_fault+0xcb0/0xd00 handle_pte_fault at mm/memory.c:4049 (inlined by) __handle_mm_fault at mm/memory.c:4163 handle_mm_fault+0xfc/0x2f0 handle_mm_fault at mm/memory.c:4200 do_page_fault+0x263/0x6f9 do_user_addr_fault at arch/x86/mm/fault.c:1465 (inlined by) do_page_fault at arch/x86/mm/fault.c:1539 page_fault+0x34/0x40 read to 0xfffffc0d48ec1a00 of 8 bytes by task 94817 on cpu 69: put_page+0x15a/0x1f0 page_zonenum at include/linux/mm.h:923 (inlined by) is_zone_device_page at include/linux/mm.h:929 (inlined by) page_is_devmap_managed at include/linux/mm.h:948 (inlined by) put_page at include/linux/mm.h:1023 wp_page_copy+0x571/0x930 wp_page_copy at mm/memory.c:2615 do_wp_page+0x107/0x7b0 __handle_mm_fault+0xcb0/0xd00 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 Reported by Kernel Concurrency Sanitizer on: CPU: 69 PID: 94817 Comm: systemd-udevd Tainted: G W O L 5.5.0-next-20200204+ #6 Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 A page never changes its zone number. The zone number happens to be stored in the same word as other bits which are modified, but the zone number bits will never be modified by any other write, so it can accept a reload of the zone bits after an intervening write and it don't need to use READ_ONCE(). Thus, annotate this data race using ASSERT_EXCLUSIVE_BITS() to also assert that there are no concurrent writes to it. Suggested-by: Marco Elver Signed-off-by: Qian Cai Signed-off-by: Andrew Morton Cc: Paul E. McKenney Cc: David Hildenbrand Cc: Jan Kara Cc: John Hubbard Cc: Ira Weiny Cc: Dan Williams Link: http://lkml.kernel.org/r/1581619089-14472-1-git-send-email-cai@lca.pw Signed-off-by: Linus Torvalds --- include/linux/mm.h | 1 + 1 file changed, 1 insertion(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index 2e7ec3ee34cf..1983e08f5906 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1067,6 +1067,7 @@ vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf); static inline enum zone_type page_zonenum(const struct page *page) { + ASSERT_EXCLUSIVE_BITS(page->flags, ZONES_MASK << ZONES_PGSHIFT); return (page->flags >> ZONES_PGSHIFT) & ZONES_MASK; }