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BUG: KCSAN: data-race in __xa_set_mark / find_get_pages_range_tag

write to 0xffff8881258f06a8 of 8 bytes by task 9228 on cpu 1:
 instrument_write include/linux/instrumented.h:42 [inline]
 __test_and_set_bit include/asm-generic/bitops/instrumented-non-atomic.h:71 [inline]
 node_set_mark lib/xarray.c:93 [inline]
 xas_set_mark lib/xarray.c:879 [inline]
 __xa_set_mark+0x233/0x330 lib/xarray.c:1708
 __set_page_dirty+0x17e/0x1d0 fs/buffer.c:610
 mark_buffer_dirty+0x12e/0x260 fs/buffer.c:1138
 __ext4_handle_dirty_metadata+0x20a/0x5a0 fs/ext4/ext4_jbd2.c:337
 ext4_do_update_inode fs/ext4/inode.c:5072 [inline]
 ext4_mark_iloc_dirty+0x1302/0x1660 fs/ext4/inode.c:5624
 __ext4_mark_inode_dirty+0x448/0x630 fs/ext4/inode.c:5818
 ext4_dirty_inode+0xa6/0xc0 fs/ext4/inode.c:5854
 __mark_inode_dirty+0x72/0x7e0 fs/fs-writeback.c:2258
 generic_update_time fs/inode.c:1762 [inline]
 update_time fs/inode.c:1775 [inline]
 touch_atime+0x157/0x1a0 fs/inode.c:1846
 file_accessed include/linux/fs.h:2229 [inline]
 iterate_dir+0x2c4/0x320 fs/readdir.c:70
 __do_sys_getdents fs/readdir.c:283 [inline]
 __se_sys_getdents+0x7f/0x190 fs/readdir.c:268
 __x64_sys_getdents+0x3f/0x50 fs/readdir.c:268
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881258f06a8 of 8 bytes by task 8941 on cpu 0:
 xas_find_chunk include/linux/xarray.h:1625 [inline]
 xas_next_marked include/linux/xarray.h:1656 [inline]
 find_get_pages_range_tag+0x30c/0x580 mm/filemap.c:1908
 pagevec_lookup_range_tag+0x37/0x50 mm/swap.c:1120
 write_cache_pages+0x1f8/0x840 mm/page-writeback.c:2205
 generic_writepages+0x64/0xa0 mm/page-writeback.c:2339
 blkdev_writepages+0x19/0x20 fs/block_dev.c:2065
 do_writepages+0x7b/0x150 mm/page-writeback.c:2354
 __filemap_fdatawrite_range+0x19b/0x1d0 mm/filemap.c:421
 __filemap_fdatawrite mm/filemap.c:429 [inline]
 filemap_flush+0x1f/0x30 mm/filemap.c:456
 __sync_blockdev+0x69/0x70 fs/block_dev.c:489
 __sync_filesystem fs/sync.c:40 [inline]
 sync_filesystem+0xcb/0x160 fs/sync.c:64
 ovl_sync_fs+0x74/0x90 fs/overlayfs/super.c:281
 __sync_filesystem fs/sync.c:39 [inline]
 sync_filesystem+0x112/0x160 fs/sync.c:67
 generic_shutdown_super+0x42/0x210 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:135
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:239 [inline]
 __prepare_exit_to_usermode+0x1c6/0x230 arch/x86/entry/common.c:269
 __syscall_return_slowpath+0x47/0x60 arch/x86/entry/common.c:352
 do_syscall_64+0x5d/0xb0 arch/x86/entry/common.c:393
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8941 Comm: syz-executor.4 Not tainted 5.8.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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