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SubjectRe: [PATCH -next v2] mm: annotate a data race in page_zonenum()
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On 2/13/20 10:38 AM, Qian Cai wrote:
> 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 <elver@google.com>
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
>
> v2: use ASSERT_EXCLUSIVE_BITS().


Much cleaner, thanks to this new macro. You can add:


Reviewed-by: John Hubbard <jhubbard@nvidia.com>


thanks,
--
John Hubbard
NVIDIA

>
> BTW, not sure if it is easier for Andrew with Paul to pick this up (with
> Andrew's ACK), since ASSERT_EXCLUSIVE_BITS() is in -rcu tree only (or likely
> tomorrow's -next tree).
>
> include/linux/mm.h | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 52269e56c514..0d70fafd055c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -920,6 +920,7 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
>
> 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;
> }
>
>

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