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BUG: KCSAN: data-race in __xa_clear_mark / xas_find_marked

write to 0xffff88811f509230 of 8 bytes by task 852 on cpu 1:
 instrument_write include/linux/instrumented.h:42 [inline]
 __instrument_read_write_bitop include/asm-generic/bitops/instrumented-non-atomic.h:79 [inline]
 __test_and_clear_bit include/asm-generic/bitops/instrumented-non-atomic.h:109 [inline]
 node_clear_mark lib/xarray.c:100 [inline]
 xas_clear_mark lib/xarray.c:911 [inline]
 __xa_clear_mark+0x1d9/0x2c0 lib/xarray.c:1917
 test_clear_page_writeback+0x23e/0x560 mm/page-writeback.c:2736
 end_page_writeback+0xd7/0x1b0 mm/filemap.c:1548
 ext4_finish_bio+0x3e2/0x430 fs/ext4/page-io.c:143
 ext4_release_io_end+0x98/0x200 fs/ext4/page-io.c:158
 ext4_end_io_end fs/ext4/page-io.c:192 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:257 [inline]
 ext4_end_io_rsv_work+0x306/0x360 fs/ext4/page-io.c:271
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2275
 worker_thread+0x636/0xae0 kernel/workqueue.c:2421
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88811f509230 of 8 bytes by task 7436 on cpu 0:
 xas_find_chunk include/linux/xarray.h:1662 [inline]
 xas_find_marked+0x195/0x5f0 lib/xarray.c:1349
 find_get_entry mm/filemap.c:1925 [inline]
 find_get_pages_range_tag+0xf2/0x390 mm/filemap.c:2216
 pagevec_lookup_range_tag+0x37/0x50 mm/swap.c:1123
 __filemap_fdatawait_range+0xab/0x1b0 mm/filemap.c:510
 filemap_fdatawait_range mm/filemap.c:545 [inline]
 filemap_write_and_wait_range+0x264/0x390 mm/filemap.c:695
 ext4_insert_range+0x2bd/0x9c0 fs/ext4/extents.c:5433
 ext4_fallocate+0x20a/0x4d0 fs/ext4/extents.c:4669
 vfs_fallocate+0x463/0x660 fs/open.c:311
 ksys_fallocate fs/open.c:334 [inline]
 __do_sys_fallocate fs/open.c:342 [inline]
 __se_sys_fallocate fs/open.c:340 [inline]
 __x64_sys_fallocate+0x75/0xc0 fs/open.c:340
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7436 Comm: syz-executor.4 Not tainted 5.13.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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