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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getpage_gfp

write to 0xffff888027656558 of 8 bytes by task 19214 on cpu 1:
 shmem_add_to_page_cache+0x5cd/0x6e0 mm/shmem.c:718
 shmem_getpage_gfp+0x86a/0x1980 mm/shmem.c:1929
 shmem_fault+0x16c/0x450 mm/shmem.c:2116
 __do_fault mm/memory.c:3637 [inline]
 do_read_fault+0x2e1/0x530 mm/memory.c:3939
 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+0x1019/0x1840 mm/memory.c:4551
 do_user_addr_fault+0x60c/0xc00 arch/x86/mm/fault.c:1390
 handle_page_fault arch/x86/mm/fault.c:1475 [inline]
 exc_page_fault+0x94/0x2a0 arch/x86/mm/fault.c:1531
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577
 copy_user_enhanced_fast_string+0xe/0x40 arch/x86/lib/copy_user_64.S:205
 copy_user_generic arch/x86/include/asm/uaccess_64.h:37 [inline]
 raw_copy_from_user arch/x86/include/asm/uaccess_64.h:52 [inline]
 copyin lib/iov_iter.c:157 [inline]
 copy_page_from_iter_iovec lib/iov_iter.c:301 [inline]
 copy_page_from_iter+0x34e/0x590 lib/iov_iter.c:933
 process_vm_rw_pages mm/process_vm_access.c:44 [inline]
 process_vm_rw_single_vec+0x294/0x460 mm/process_vm_access.c:118
 process_vm_rw_core mm/process_vm_access.c:216 [inline]
 process_vm_rw+0x3a3/0x540 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+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888027656558 of 8 bytes by task 19215 on cpu 0:
 shmem_recalc_inode mm/shmem.c:367 [inline]
 shmem_getpage_gfp+0xba0/0x1980 mm/shmem.c:1939
 shmem_fault+0x16c/0x450 mm/shmem.c:2116
 __do_fault mm/memory.c:3637 [inline]
 do_read_fault+0x2e1/0x530 mm/memory.c:3939
 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+0x1019/0x1840 mm/memory.c:4551
 faultin_page mm/gup.c:850 [inline]
 __get_user_pages+0xa47/0x1000 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:2570 [inline]
 __do_sys_remap_file_pages+0x4c0/0x6a0 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+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 19215 Comm: syz-executor.5 Tainted: G        W         5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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