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BUG: KCSAN: data-race in mb_mark_used / mb_update_avg_fragment_size

write to 0xffff888100469794 of 4 bytes by task 25694 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_check_limits fs/ext4/mballoc.c:2086 [inline]
 ext4_mb_complex_scan_group+0x7ee/0x850 fs/ext4/mballoc.c:2366
 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_alloc_file_blocks+0x271/0x720 fs/ext4/extents.c:4425
 ext4_fallocate+0x2a7/0x4d0 fs/ext4/extents.c:4705
 vfs_fallocate+0x463/0x660 fs/open.c:311
 ksys_fallocate fs/open.c:334 [inline]
 __do_sys_fallocate fs/open.c:342 [inline]
 __se_sys_fallocate fs/open.c:340 [inline]
 __x64_sys_fallocate+0x75/0xc0 fs/open.c:340
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888100469794 of 4 bytes by task 25687 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_free_blocks+0x9e4/0xb40 fs/ext4/mballoc.c:1856
 ext4_free_blocks+0x1418/0x1b50 fs/ext4/mballoc.c:5988
 ext4_remove_blocks+0x61a/0x800 fs/ext4/extents.c:2498
 ext4_ext_rm_leaf+0x670/0xd20 fs/ext4/extents.c:2664
 ext4_ext_remove_space+0x901/0x1300 fs/ext4/extents.c:2912
 ext4_punch_hole+0x6b8/0x9a0 fs/ext4/inode.c:4113
 ext4_fallocate+0xea/0x4d0 fs/ext4/extents.c:4655
 vfs_fallocate+0x463/0x660 fs/open.c:311
 ksys_fallocate fs/open.c:334 [inline]
 __do_sys_fallocate fs/open.c:342 [inline]
 __se_sys_fallocate fs/open.c:340 [inline]
 __x64_sys_fallocate+0x75/0xc0 fs/open.c:340
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 25687 Comm: syz-executor.3 Tainted: G        W         5.13.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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