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BUG: KCSAN: data-race in mb_free_blocks / mb_update_avg_fragment_size

write to 0xffff8881017636d8 of 4 bytes by task 1765 on cpu 0:
 mb_free_blocks+0x323/0xb40 fs/ext4/mballoc.c:1833
 ext4_free_blocks+0x1418/0x1b50 fs/ext4/mballoc.c:5988
 ext4_clear_blocks+0x292/0x2b0 fs/ext4/indirect.c:877
 ext4_free_data+0x1b0/0x2b0 fs/ext4/indirect.c:950
 ext4_free_branches+0x64/0x420 fs/ext4/indirect.c:1095
 ext4_free_branches+0x21b/0x420 fs/ext4/indirect.c:1030
 ext4_ind_truncate+0x751/0x880 fs/ext4/indirect.c:1181
 ext4_truncate+0x756/0xa80 fs/ext4/inode.c:4264
 ext4_evict_inode+0xa54/0xdb0 fs/ext4/inode.c:288
 evict+0x1c8/0x3c0 fs/inode.c:584
 iput_final fs/inode.c:1660 [inline]
 iput+0x433/0x590 fs/inode.c:1686
 do_unlinkat+0x293/0x4f0 fs/namei.c:4099
 __do_sys_unlink fs/namei.c:4139 [inline]
 __se_sys_unlink fs/namei.c:4137 [inline]
 __x64_sys_unlink+0x2c/0x30 fs/namei.c:4137
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881017636d8 of 4 bytes by task 1766 on cpu 1:
 ext4_mb_avg_fragment_size_cmp fs/ext4/mballoc.c:834 [inline]
 ext4_mb_rb_insert fs/ext4/mballoc.c:811 [inline]
 mb_update_avg_fragment_size+0x161/0x260 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_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:4241
 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:2885
 ext4_mkdir+0x329/0x760 fs/ext4/namei.c:2931
 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

value changed: 0x0000000a -> 0x00000009

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1766 Comm: syz-executor.4 Not tainted 5.13.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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