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BUG: KCSAN: data-race in mb_mark_used / mb_update_avg_fragment_size

write to 0xffff88810041fb54 of 4 bytes by task 1790 on cpu 1:
 mb_mark_used+0x13b/0xc50 fs/ext4/mballoc.c:1942
 ext4_mb_use_best_found+0x102/0x320 fs/ext4/mballoc.c:2014
 ext4_mb_measure_extent fs/ext4/mballoc.c:2130 [inline]
 ext4_mb_complex_scan_group+0x349/0x850 fs/ext4/mballoc.c:2360
 ext4_mb_regular_allocator+0x1a22/0x2520 fs/ext4/mballoc.c:2759
 ext4_mb_new_blocks+0x762/0x1f90 fs/ext4/mballoc.c:5514
 ext4_ext_map_blocks+0x1569/0x1f00 fs/ext4/extents.c:4238
 ext4_map_blocks+0x70d/0xef0 fs/ext4/inode.c:638
 ext4_getblk+0xb1/0x3d0 fs/ext4/inode.c:848
 ext4_bread+0x28/0x130 fs/ext4/inode.c:900
 ext4_append+0xd1/0x1c0 fs/ext4/namei.c:67
 ext4_init_new_dir+0x177/0x500 fs/ext4/namei.c:2883
 ext4_mkdir+0x329/0x760 fs/ext4/namei.c:2929
 vfs_mkdir+0x2a4/0x370 fs/namei.c:3813
 do_mkdirat+0x11d/0x200 fs/namei.c:3838
 __do_sys_mkdir fs/namei.c:3856 [inline]
 __se_sys_mkdir fs/namei.c:3854 [inline]
 __x64_sys_mkdir+0x32/0x40 fs/namei.c:3854
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88810041fb54 of 4 bytes by task 1794 on cpu 0:
 ext4_mb_avg_fragment_size_cmp fs/ext4/mballoc.c:835 [inline]
 ext4_mb_rb_insert fs/ext4/mballoc.c:811 [inline]
 mb_update_avg_fragment_size+0x184/0x260 fs/ext4/mballoc.c:859
 mb_mark_used+0xae0/0xc50 fs/ext4/mballoc.c:1993
 ext4_mb_use_best_found+0x102/0x320 fs/ext4/mballoc.c:2014
 ext4_mb_simple_scan_group+0x253/0x3a0 fs/ext4/mballoc.c:2292
 ext4_mb_regular_allocator+0x1974/0x2520 fs/ext4/mballoc.c:2754
 ext4_mb_new_blocks+0x762/0x1f90 fs/ext4/mballoc.c:5514
 ext4_ext_map_blocks+0x1569/0x1f00 fs/ext4/extents.c:4238
 ext4_map_blocks+0x70d/0xef0 fs/ext4/inode.c:638
 mpage_map_one_extent+0x10d/0x360 fs/ext4/inode.c:2395
 mpage_map_and_submit_extent fs/ext4/inode.c:2448 [inline]
 ext4_writepages+0xc1a/0x1d10 fs/ext4/inode.c:2800
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __writeback_single_inode+0x80/0x450 fs/fs-writeback.c:1467
 writeback_sb_inodes+0x564/0xf10 fs/fs-writeback.c:1732
 __writeback_inodes_wb fs/fs-writeback.c:1801 [inline]
 wb_writeback+0x327/0x700 fs/fs-writeback.c:1907
 wb_check_old_data_flush fs/fs-writeback.c:2009 [inline]
 wb_do_writeback+0x461/0x510 fs/fs-writeback.c:2062
 wb_workfn+0xc8/0x520 fs/fs-writeback.c:2091
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1794 Comm: kworker/u4:4 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
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