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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_getpage_gfp

write to 0xffff88810d05c698 of 8 bytes by task 17697 on cpu 0:
 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_shared_fault+0xc3/0x680 mm/memory.c:3993
 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+0x12b0/0x1840 mm/memory.c:4551
 faultin_page mm/gup.c:850 [inline]
 __get_user_pages+0xa47/0x1000 mm/gup.c:1069
 __get_user_pages_locked mm/gup.c:1255 [inline]
 __get_user_pages_remote+0x4e6/0x6e0 mm/gup.c:1722
 pin_user_pages_remote+0x58/0x80 mm/gup.c:2790
 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 0xffff88810d05c698 of 8 bytes by task 17748 on cpu 1:
 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_shared_fault+0xc3/0x680 mm/memory.c:3993
 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+0x12b0/0x1840 mm/memory.c:4551
 faultin_page mm/gup.c:850 [inline]
 __get_user_pages+0xa47/0x1000 mm/gup.c:1069
 __get_user_pages_locked mm/gup.c:1255 [inline]
 __get_user_pages_remote+0x4e6/0x6e0 mm/gup.c:1722
 pin_user_pages_remote+0x58/0x80 mm/gup.c:2790
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17748 Comm: syz-executor.0 Not tainted 5.12.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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