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BUG: KCSAN: data-race in expand_downwards / page_add_new_anon_rmap

write to 0xffff888030e9e708 of 8 bytes by task 27363 on cpu 0:
 expand_downwards+0x69d/0x990 mm/mmap.c:2552
 expand_stack+0x19/0x20 mm/mmap.c:2609
 do_user_addr_fault+0x71e/0x830 arch/x86/mm/fault.c:1365
 handle_page_fault arch/x86/mm/fault.c:1450 [inline]
 exc_page_fault+0x94/0x2a0 arch/x86/mm/fault.c:1506
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:580
 do_strncpy_from_user lib/strncpy_from_user.c:37 [inline]
 strncpy_from_user+0xf0/0x250 lib/strncpy_from_user.c:139
 getname_flags+0xb8/0x3d0 fs/namei.c:149
 getname+0x15/0x20 fs/namei.c:209
 do_sys_openat2+0x5b/0x240 fs/open.c:1166
 do_sys_open fs/open.c:1188 [inline]
 __do_sys_openat fs/open.c:1204 [inline]
 __se_sys_openat fs/open.c:1199 [inline]
 __x64_sys_openat+0xef/0x110 fs/open.c:1199
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888030e9e708 of 8 bytes by task 27361 on cpu 1:
 linear_page_index include/linux/pagemap.h:557 [inline]
 __page_set_anon_rmap mm/rmap.c:1065 [inline]
 page_add_new_anon_rmap+0x2a5/0x330 mm/rmap.c:1197
 do_anonymous_page+0x81a/0xd20 mm/memory.c:3572
 handle_pte_fault mm/memory.c:4383 [inline]
 __handle_mm_fault mm/memory.c:4520 [inline]
 handle_mm_fault+0x1005/0x17b0 mm/memory.c:4618
 faultin_page mm/gup.c:851 [inline]
 __get_user_pages+0xa32/0xff0 mm/gup.c:1070
 populate_vma_page_range mm/gup.c:1403 [inline]
 __mm_populate+0x24d/0x380 mm/gup.c:1451
 mm_populate include/linux/mm.h:2573 [inline]
 vm_mmap_pgoff+0x14c/0x1d0 mm/util.c:524
 ksys_mmap_pgoff+0xe1/0x380 mm/mmap.c:1634
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 27361 Comm: syz-executor.0 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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