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BUG: KCSAN: data-race in __xa_set_mark / find_get_pages_range_tag

read-write to 0xffff8881074988e8 of 8 bytes by task 8453 on cpu 1:
 instrument_read_write include/linux/instrumented.h:57 [inline]
 __instrument_read_write_bitop include/asm-generic/bitops/instrumented-non-atomic.h:81 [inline]
 __test_and_set_bit include/asm-generic/bitops/instrumented-non-atomic.h:95 [inline]
 node_set_mark lib/xarray.c:93 [inline]
 xas_set_mark lib/xarray.c:882 [inline]
 __xa_set_mark+0xd0/0x190 lib/xarray.c:1898
 __set_page_dirty+0x17e/0x1d0 fs/buffer.c:609
 mark_buffer_dirty+0x126/0x230 fs/buffer.c:1137
 __ext4_handle_dirty_metadata+0x20a/0x590 fs/ext4/ext4_jbd2.c:362
 ext4_do_update_inode fs/ext4/inode.c:5132 [inline]
 ext4_mark_iloc_dirty+0x12ed/0x1650 fs/ext4/inode.c:5709
 __ext4_mark_inode_dirty+0x450/0x610 fs/ext4/inode.c:5903
 ext4_rmdir+0x8be/0x950 fs/ext4/namei.c:3179
 vfs_rmdir+0x135/0x290 fs/namei.c:3712
 do_rmdir+0x16e/0x300 fs/namei.c:3773
 __do_sys_rmdir fs/namei.c:3791 [inline]
 __se_sys_rmdir fs/namei.c:3789 [inline]
 __x64_sys_rmdir+0x2c/0x30 fs/namei.c:3789
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881074988e8 of 8 bytes by task 8457 on cpu 0:
 xas_find_chunk include/linux/xarray.h:1660 [inline]
 xas_next_marked include/linux/xarray.h:1691 [inline]
 find_get_pages_range_tag+0x35c/0x600 mm/filemap.c:2094
 pagevec_lookup_range_tag+0x37/0x50 mm/swap.c:1161
 write_cache_pages+0x1e9/0x7f0 mm/page-writeback.c:2203
 generic_writepages+0x64/0xa0 mm/page-writeback.c:2337
 blkdev_writepages+0x19/0x20 fs/block_dev.c:1946
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range+0x19d/0x1d0 mm/filemap.c:422
 __filemap_fdatawrite mm/filemap.c:430 [inline]
 filemap_flush+0x1f/0x30 mm/filemap.c:457
 __sync_blockdev+0x69/0x70 fs/block_dev.c:508
 __sync_filesystem fs/sync.c:40 [inline]
 sync_filesystem+0xcb/0x160 fs/sync.c:64
 ovl_sync_fs+0x94/0xc0 fs/overlayfs/super.c:283
 __sync_filesystem fs/sync.c:39 [inline]
 sync_filesystem+0x112/0x160 fs/sync.c:67
 generic_shutdown_super+0x3c/0x1f0 fs/super.c:448
 kill_anon_super+0x23/0x40 fs/super.c:1108
 deactivate_locked_super+0x6a/0xb0 fs/super.c:335
 deactivate_super+0x85/0x90 fs/super.c:366
 cleanup_mnt+0x277/0x2e0 fs/namespace.c:1118
 __cleanup_mnt+0x15/0x20 fs/namespace.c:1125
 task_work_run+0x8e/0x110 kernel/task_work.c:151
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:164 [inline]
 exit_to_user_mode_prepare+0x13c/0x170 kernel/entry/common.c:191
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:266
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8457 Comm: syz-executor.2 Not tainted 5.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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