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BUG: KCSAN: data-race in shmem_add_to_page_cache / shmem_recalc_inode

write to 0xffff888122c25f10 of 8 bytes by task 12743 on cpu 1:
 shmem_add_to_page_cache+0x497/0x6b0 mm/shmem.c:643
 shmem_getpage_gfp+0x3fd/0x1390 mm/shmem.c:1876
 shmem_fault+0x114/0x470 mm/shmem.c:2067
 __do_fault+0xae/0x1f0 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+0x1ddb/0x2e00 mm/memory.c:4163
 handle_mm_fault+0x21b/0x530 mm/memory.c:4200
 faultin_page mm/gup.c:659 [inline]
 __get_user_pages+0x485/0x1130 mm/gup.c:870
 __get_user_pages_locked mm/gup.c:1057 [inline]
 get_user_pages_remote+0x227/0x440 mm/gup.c:1654
 pin_user_pages_remote+0x50/0x70 mm/gup.c:2551
 process_vm_rw_single_vec mm/process_vm_access.c:108 [inline]
 process_vm_rw_core.isra.0+0x38f/0x820 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+0x8b/0xb0 mm/process_vm_access.c:303
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888122c25f10 of 8 bytes by task 12695 on cpu 0:
 shmem_recalc_inode+0x54/0x190 mm/shmem.c:306
 shmem_getpage_gfp+0x552/0x1390 mm/shmem.c:1890
 shmem_fault+0x114/0x470 mm/shmem.c:2067
 __do_fault+0xae/0x1f0 mm/memory.c:3276
 do_read_fault mm/memory.c:3673 [inline]
 do_fault mm/memory.c:3802 [inline]
 handle_pte_fault mm/memory.c:4033 [inline]
 __handle_mm_fault+0x270d/0x2e00 mm/memory.c:4163
 handle_mm_fault+0x21b/0x530 mm/memory.c:4200
 faultin_page mm/gup.c:659 [inline]
 __get_user_pages+0x485/0x1130 mm/gup.c:870
 populate_vma_page_range+0xe6/0x100 mm/gup.c:1181
 __mm_populate+0x168/0x2a0 mm/gup.c:1229
 mm_populate include/linux/mm.h:2343 [inline]
 vm_mmap_pgoff+0x181/0x190 mm/util.c:511
 ksys_mmap_pgoff+0x99/0x420 mm/mmap.c:1597
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:99 [inline]
 __se_sys_mmap arch/x86/kernel/sys_x86_64.c:90 [inline]
 __x64_sys_mmap+0x2e/0x40 arch/x86/kernel/sys_x86_64.c:90
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 12695 Comm: syz-executor.5 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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