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BUG: KCSAN: data-race in __delete_from_page_cache / shmem_mfill_atomic_pte

read-write to 0xffff888128b66868 of 8 bytes by task 9460 on cpu 1:
 page_cache_delete mm/filemap.c:154 [inline]
 __delete_from_page_cache+0x26c/0x340 mm/filemap.c:239
 delete_from_page_cache+0x84/0x260 mm/filemap.c:274
 truncate_inode_page+0x41/0x50 mm/truncate.c:228
 shmem_undo_range+0x3fc/0x1110 mm/shmem.c:949
 shmem_truncate_range mm/shmem.c:1058 [inline]
 shmem_fallocate+0x28e/0x870 mm/shmem.c:2805
 vfs_fallocate+0x471/0x6c0 fs/open.c:309
 madvise_remove mm/madvise.c:865 [inline]
 madvise_vma mm/madvise.c:939 [inline]
 do_madvise+0x7e1/0x1480 mm/madvise.c:1144
 __do_sys_madvise mm/madvise.c:1170 [inline]
 __se_sys_madvise mm/madvise.c:1168 [inline]
 __x64_sys_madvise+0x5d/0x70 mm/madvise.c:1168
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888128b66868 of 8 bytes by task 9449 on cpu 0:
 shmem_recalc_inode mm/shmem.c:367 [inline]
 shmem_mfill_atomic_pte+0x8c6/0xe90 mm/shmem.c:2457
 shmem_mcopy_atomic_pte+0x3a/0x50 mm/shmem.c:2490
 mfill_atomic_pte mm/userfaultfd.c:446 [inline]
 __mcopy_atomic mm/userfaultfd.c:579 [inline]
 mcopy_atomic+0x543/0x1390 mm/userfaultfd.c:629
 userfaultfd_copy fs/userfaultfd.c:1696 [inline]
 userfaultfd_ioctl+0x1153/0x24e0 fs/userfaultfd.c:1894
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9449 Comm: syz-executor.3 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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