syzbot

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BUG: KCSAN: data-race in expand_downwards / page_add_new_anon_rmap

write to 0xffff88811fa05960 of 8 bytes by task 3369 on cpu 0:
 expand_downwards+0x6d0/0x9c0 mm/mmap.c:2486
 expand_stack+0x19/0x20 mm/mmap.c:2543
 do_user_addr_fault+0x6d9/0x810 arch/x86/mm/fault.c:1267
 handle_page_fault arch/x86/mm/fault.c:1365 [inline]
 exc_page_fault+0xb8/0x330 arch/x86/mm/fault.c:1418
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:544
 do_strncpy_from_user lib/strncpy_from_user.c:40 [inline]
 strncpy_from_user+0x103/0x2e0 lib/strncpy_from_user.c:121
 getname_flags+0xb8/0x3d0 fs/namei.c:149
 getname+0x15/0x20 fs/namei.c:209
 do_sys_openat2+0x2f3/0x4a0 fs/open.c:1173
 do_sys_open fs/open.c:1195 [inline]
 __do_sys_openat fs/open.c:1209 [inline]
 __se_sys_openat fs/open.c:1204 [inline]
 __x64_sys_openat+0xef/0x110 fs/open.c:1204
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811fa05960 of 8 bytes by task 3365 on cpu 1:
 linear_page_index include/linux/pagemap.h:494 [inline]
 __page_set_anon_rmap mm/rmap.c:1059 [inline]
 page_add_new_anon_rmap+0x438/0x530 mm/rmap.c:1191
 do_anonymous_page+0x99f/0xec0 mm/memory.c:3413
 handle_pte_fault mm/memory.c:4223 [inline]
 __handle_mm_fault mm/memory.c:4357 [inline]
 handle_mm_fault+0x1371/0x1930 mm/memory.c:4394
 faultin_page mm/gup.c:887 [inline]
 __get_user_pages+0xac6/0x1150 mm/gup.c:1113
 populate_vma_page_range mm/gup.c:1452 [inline]
 __mm_populate+0x256/0x340 mm/gup.c:1500
 mm_populate include/linux/mm.h:2605 [inline]
 vm_mmap_pgoff+0x13b/0x170 mm/util.c:511
 ksys_mmap_pgoff+0xdf/0x3a0 mm/mmap.c:1595
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3365 Comm: syz-executor.5 Not tainted 5.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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