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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_recalc_inode

write to 0xffff88803aa30e08 of 8 bytes by task 13284 on cpu 1:
 shmem_add_to_page_cache+0x4b0/0x6c0 mm/shmem.c:643
 shmem_getpage_gfp+0x43f/0x1520 mm/shmem.c:1871
 shmem_fault+0x117/0x4b0 mm/shmem.c:2062
 __do_fault+0xa8/0x1e0 mm/memory.c:3450
 do_shared_fault mm/memory.c:3901 [inline]
 do_fault mm/memory.c:3979 [inline]
 handle_pte_fault mm/memory.c:4215 [inline]
 __handle_mm_fault+0x24d9/0x2ec0 mm/memory.c:4345
 handle_mm_fault+0x21c/0x540 mm/memory.c:4382
 faultin_page mm/gup.c:879 [inline]
 __get_user_pages+0x533/0x11c0 mm/gup.c:1098
 __get_user_pages_locked mm/gup.c:1284 [inline]
 __get_user_pages_remote mm/gup.c:1835 [inline]
 __get_user_pages_remote+0x164/0x590 mm/gup.c:1810
 pin_user_pages_remote+0x71/0xb0 mm/gup.c:2901
 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+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88803aa30e08 of 8 bytes by task 13290 on cpu 0:
 shmem_recalc_inode+0x50/0x180 mm/shmem.c:306
 shmem_getpage_gfp+0x5ca/0x1520 mm/shmem.c:1885
 shmem_fault+0x117/0x4b0 mm/shmem.c:2062
 __do_fault+0xa8/0x1e0 mm/memory.c:3450
 do_read_fault mm/memory.c:3846 [inline]
 do_fault mm/memory.c:3975 [inline]
 handle_pte_fault mm/memory.c:4215 [inline]
 __handle_mm_fault+0x2679/0x2ec0 mm/memory.c:4345
 handle_mm_fault+0x21c/0x540 mm/memory.c:4382
 faultin_page mm/gup.c:879 [inline]
 __get_user_pages+0x533/0x11c0 mm/gup.c:1098
 populate_vma_page_range+0xdc/0x100 mm/gup.c:1430
 __mm_populate+0x168/0x2b0 mm/gup.c:1478
 mm_populate include/linux/mm.h:2562 [inline]
 vm_mmap_pgoff+0x185/0x190 mm/util.c:511
 ksys_mmap_pgoff+0x96/0x420 mm/mmap.c:1595
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 13290 Comm: syz-executor.2 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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