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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getpage_gfp

write to 0xffff888103f4a780 of 8 bytes by task 13152 on cpu 1:
 shmem_add_to_page_cache+0x52d/0x650 mm/shmem.c:718
 shmem_getpage_gfp+0xbdc/0x1410 mm/shmem.c:1929
 shmem_fault+0x16d/0x500 mm/shmem.c:2116
 __do_fault mm/memory.c:3637 [inline]
 do_read_fault mm/memory.c:3939 [inline]
 do_fault mm/memory.c:4067 [inline]
 handle_pte_fault mm/memory.c:4318 [inline]
 __handle_mm_fault mm/memory.c:4453 [inline]
 handle_mm_fault+0xe8d/0x1a70 mm/memory.c:4551
 faultin_page mm/gup.c:850 [inline]
 __get_user_pages+0x947/0xee0 mm/gup.c:1069
 populate_vma_page_range mm/gup.c:1402 [inline]
 __mm_populate+0x24d/0x380 mm/gup.c:1450
 mm_populate include/linux/mm.h:2582 [inline]
 __do_sys_remap_file_pages+0x56d/0x6f0 mm/mmap.c:3052
 __se_sys_remap_file_pages mm/mmap.c:2962 [inline]
 __x64_sys_remap_file_pages+0x63/0x70 mm/mmap.c:2962
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888103f4a780 of 8 bytes by task 13139 on cpu 0:
 shmem_recalc_inode mm/shmem.c:367 [inline]
 shmem_getpage_gfp+0x1017/0x1410 mm/shmem.c:1939
 shmem_fault+0x16d/0x500 mm/shmem.c:2116
 __do_fault mm/memory.c:3637 [inline]
 do_shared_fault mm/memory.c:3993 [inline]
 do_fault mm/memory.c:4071 [inline]
 handle_pte_fault mm/memory.c:4318 [inline]
 __handle_mm_fault mm/memory.c:4453 [inline]
 handle_mm_fault+0xf76/0x1a70 mm/memory.c:4551
 faultin_page mm/gup.c:850 [inline]
 __get_user_pages+0x947/0xee0 mm/gup.c:1069
 __get_user_pages_locked mm/gup.c:1255 [inline]
 __get_user_pages_remote+0x446/0x600 mm/gup.c:1726
 pin_user_pages_remote+0x58/0x80 mm/gup.c:2794
 process_vm_rw_single_vec+0x17d/0x460 mm/process_vm_access.c:106
 process_vm_rw_core mm/process_vm_access.c:216 [inline]
 process_vm_rw+0x347/0x4e0 mm/process_vm_access.c:284
 __do_sys_process_vm_writev mm/process_vm_access.c:304 [inline]
 __se_sys_process_vm_writev mm/process_vm_access.c:299 [inline]
 __x64_sys_process_vm_writev+0x76/0x90 mm/process_vm_access.c:299
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 13139 Comm: syz-executor.4 Not tainted 5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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