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BUG: KCSAN: data-race in __writeback_single_inode / xas_set_mark

write to 0xffff88810187cbac of 4 bytes by task 1795 on cpu 0:
 xa_mark_set lib/xarray.c:69 [inline]
 xas_set_mark+0x13e/0x150 lib/xarray.c:889
 tag_pages_for_writeback+0x9d/0x2e0 mm/page-writeback.c:2125
 write_cache_pages+0x184/0x820 mm/page-writeback.c:2195
 generic_writepages+0x6a/0xa0 mm/page-writeback.c:2338
 blkdev_writepages+0x19/0x20 fs/block_dev.c:1496
 do_writepages+0x8b/0x160 mm/page-writeback.c:2353
 __filemap_fdatawrite_range mm/filemap.c:415 [inline]
 filemap_write_and_wait_range+0x229/0x3b0 mm/filemap.c:688
 filemap_write_and_wait include/linux/fs.h:2858 [inline]
 __sync_blockdev fs/block_dev.c:529 [inline]
 sync_blockdev+0x3e/0x50 fs/block_dev.c:538
 kill_block_super+0x52/0x90 fs/super.c:1396
 deactivate_locked_super+0x65/0xd0 fs/super.c:335
 deactivate_super+0x85/0x90 fs/super.c:366
 cleanup_mnt+0x267/0x2d0 fs/namespace.c:1136
 __cleanup_mnt+0x15/0x20 fs/namespace.c:1143
 task_work_run+0xae/0x130 kernel/task_work.c:164
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:175 [inline]
 exit_to_user_mode_prepare+0x156/0x190 kernel/entry/common.c:209
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x49/0x90 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88810187cbac of 4 bytes by task 224 on cpu 1:
 xa_marked include/linux/xarray.h:418 [inline]
 mapping_tagged include/linux/fs.h:496 [inline]
 __writeback_single_inode+0x209/0x440 fs/fs-writeback.c:1664
 writeback_sb_inodes+0x563/0xd30 fs/fs-writeback.c:1878
 __writeback_inodes_wb fs/fs-writeback.c:1947 [inline]
 wb_writeback+0x327/0x700 fs/fs-writeback.c:2053
 wb_check_background_flush fs/fs-writeback.c:2121 [inline]
 wb_do_writeback+0x4ce/0x510 fs/fs-writeback.c:2209
 wb_workfn+0xc8/0x520 fs/fs-writeback.c:2237
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
 process_scheduled_works kernel/workqueue.c:2338 [inline]
 worker_thread+0x7ff/0xae0 kernel/workqueue.c:2424
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

value changed: 0x02000021 -> 0x04000021

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 224 Comm: kworker/u4:3 Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-7:3)
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