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BUG: KCSAN: data-race in mb_free_blocks / mb_update_avg_fragment_size

write to 0xffff8881013cba98 of 4 bytes by task 5414 on cpu 1:
 mb_free_blocks+0x323/0xb40 fs/ext4/mballoc.c:1833
 ext4_free_blocks+0x1418/0x1b50 fs/ext4/mballoc.c:5988
 ext4_ext_try_to_merge_up fs/ext4/extents.c:1830 [inline]
 ext4_ext_try_to_merge+0x2fa/0x310 fs/ext4/extents.c:1857
 ext4_convert_unwritten_extents_endio fs/ext4/extents.c:3724 [inline]
 ext4_ext_handle_unwritten_extents+0x67a/0xaa0 fs/ext4/extents.c:3852
 ext4_ext_map_blocks+0x719/0x1f00 fs/ext4/extents.c:4122
 ext4_map_blocks+0x70d/0xef0 fs/ext4/inode.c:638
 ext4_convert_unwritten_extents+0x15a/0x2c0 fs/ext4/extents.c:4763
 ext4_convert_unwritten_io_end_vec+0xa4/0x130 fs/ext4/extents.c:4802
 ext4_end_io_end fs/ext4/page-io.c:184 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:257 [inline]
 ext4_end_io_rsv_work+0x198/0x360 fs/ext4/page-io.c:271
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
 worker_thread+0x636/0xae0 kernel/workqueue.c:2422
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8881013cba98 of 4 bytes by task 10040 on cpu 0:
 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_try_best_found+0x234/0x3d0 fs/ext4/mballoc.c:2180
 ext4_mb_regular_allocator+0x22bd/0x2520 fs/ext4/mballoc.c:2778
 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_alloc_file_blocks+0x271/0x720 fs/ext4/extents.c:4428
 ext4_zero_range+0x4dc/0xa40 fs/ext4/extents.c:4576
 ext4_fallocate+0x226/0x4d0 fs/ext4/extents.c:4677
 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

value changed: 0x00000013 -> 0x00000014

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10040 Comm: syz-executor.2 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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