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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getpage_gfp

write to 0xffff888108d5abb8 of 8 bytes by task 10600 on cpu 1:
 shmem_add_to_page_cache+0x5a0/0x6b0 mm/shmem.c:718
 shmem_getpage_gfp+0x829/0x1930 mm/shmem.c:1929
 shmem_fault+0x16c/0x450 mm/shmem.c:2116
 __do_fault mm/memory.c:3637 [inline]
 do_shared_fault+0xc3/0x680 mm/memory.c:3995
 do_fault mm/memory.c:4073 [inline]
 handle_pte_fault mm/memory.c:4320 [inline]
 __handle_mm_fault mm/memory.c:4455 [inline]
 handle_mm_fault+0x12f0/0x18a0 mm/memory.c:4553
 faultin_page mm/gup.c:851 [inline]
 __get_user_pages+0xa47/0x1000 mm/gup.c:1070
 __get_user_pages_locked mm/gup.c:1256 [inline]
 __get_user_pages_remote+0x4e6/0x6e0 mm/gup.c:1723
 pin_user_pages_remote+0x58/0x80 mm/gup.c:2791
 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+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 0xffff888108d5abb8 of 8 bytes by task 10526 on cpu 0:
 shmem_recalc_inode mm/shmem.c:367 [inline]
 shmem_getpage_gfp+0xb5c/0x1930 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:3941
 do_fault mm/memory.c:4069 [inline]
 handle_pte_fault mm/memory.c:4320 [inline]
 __handle_mm_fault mm/memory.c:4455 [inline]
 handle_mm_fault+0x1044/0x18a0 mm/memory.c:4553
 do_user_addr_fault+0x60c/0xc00 arch/x86/mm/fault.c:1384
 handle_page_fault arch/x86/mm/fault.c:1469 [inline]
 exc_page_fault+0x94/0x2a0 arch/x86/mm/fault.c:1525
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:580
 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:947
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10526 Comm: syz-executor.0 Not tainted 5.11.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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