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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_recalc_inode

write to 0xffff88808d1c9e10 of 8 bytes by task 17809 on cpu 1:
 shmem_add_to_page_cache+0x4b0/0x6c0 mm/shmem.c:643
 shmem_getpage_gfp+0x43f/0x14c0 mm/shmem.c:1876
 shmem_fault+0x117/0x480 mm/shmem.c:2067
 __do_fault+0xa8/0x1e0 mm/memory.c:3276
 do_shared_fault mm/memory.c:3728 [inline]
 do_fault mm/memory.c:3806 [inline]
 handle_pte_fault mm/memory.c:4033 [inline]
 __handle_mm_fault+0x1d2d/0x2cf0 mm/memory.c:4163
 handle_mm_fault+0x21c/0x540 mm/memory.c:4200
 faultin_page mm/gup.c:659 [inline]
 __get_user_pages+0x485/0x1140 mm/gup.c:870
 __get_user_pages_locked mm/gup.c:1057 [inline]
 get_user_pages_remote+0x22c/0x450 mm/gup.c:1654
 pin_user_pages_remote+0x4a/0x70 mm/gup.c:2551
 process_vm_rw_single_vec mm/process_vm_access.c:108 [inline]
 process_vm_rw_core.isra.0+0x34d/0x760 mm/process_vm_access.c:218
 process_vm_rw+0x1c4/0x1e0 mm/process_vm_access.c:286
 __do_sys_process_vm_writev mm/process_vm_access.c:308 [inline]
 __se_sys_process_vm_writev mm/process_vm_access.c:303 [inline]
 __x64_sys_process_vm_writev+0x80/0xa0 mm/process_vm_access.c:303
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88808d1c9e10 of 8 bytes by task 17855 on cpu 0:
 shmem_recalc_inode+0x50/0x180 mm/shmem.c:306
 shmem_getpage_gfp+0x5ca/0x14c0 mm/shmem.c:1890
 shmem_fault+0x117/0x480 mm/shmem.c:2067
 __do_fault+0xa8/0x1e0 mm/memory.c:3276
 do_shared_fault mm/memory.c:3728 [inline]
 do_fault mm/memory.c:3806 [inline]
 handle_pte_fault mm/memory.c:4033 [inline]
 __handle_mm_fault+0x1d2d/0x2cf0 mm/memory.c:4163
 handle_mm_fault+0x21c/0x540 mm/memory.c:4200
 faultin_page mm/gup.c:659 [inline]
 __get_user_pages+0x485/0x1140 mm/gup.c:870
 __get_user_pages_locked mm/gup.c:1057 [inline]
 get_user_pages_remote+0x22c/0x450 mm/gup.c:1654
 pin_user_pages_remote+0x4a/0x70 mm/gup.c:2551
 process_vm_rw_single_vec mm/process_vm_access.c:108 [inline]
 process_vm_rw_core.isra.0+0x34d/0x760 mm/process_vm_access.c:218
 process_vm_rw+0x1c4/0x1e0 mm/process_vm_access.c:286
 __do_sys_process_vm_writev mm/process_vm_access.c:308 [inline]
 __se_sys_process_vm_writev mm/process_vm_access.c:303 [inline]
 __x64_sys_process_vm_writev+0x80/0xa0 mm/process_vm_access.c:303
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 17855 Comm: syz-executor.2 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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