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BUG: KCSAN: data-race in mb_mark_used / mb_update_avg_fragment_size

write to 0xffff8881013d8b58 of 4 bytes by task 1770 on cpu 1:
 mb_mark_used+0x2f2/0xc50 fs/ext4/mballoc.c:1954
 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 0xffff8881013d8b58 of 4 bytes by task 1744 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_find_by_goal+0x5c3/0x890 fs/ext4/mballoc.c:2226
 ext4_mb_regular_allocator+0x11c/0x2520 fs/ext4/mballoc.c:2635
 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_get_block+0xf6/0x290 fs/ext4/inode.c:794
 ext4_get_block+0x35/0x40 fs/ext4/inode.c:811
 __block_write_begin_int+0x4a2/0x1060 fs/buffer.c:2031
 __block_write_begin fs/buffer.c:2081 [inline]
 block_page_mkwrite+0x153/0x320 fs/buffer.c:2544
 ext4_page_mkwrite+0x2d5/0xf20 fs/ext4/inode.c:6141
 do_page_mkwrite mm/memory.c:2763 [inline]
 do_shared_fault mm/memory.c:4044 [inline]
 do_fault mm/memory.c:4112 [inline]
 handle_pte_fault mm/memory.c:4367 [inline]
 __handle_mm_fault mm/memory.c:4502 [inline]
 handle_mm_fault+0x10a9/0x1a70 mm/memory.c:4600
 do_user_addr_fault+0x60c/0xc00 arch/x86/mm/fault.c:1390
 handle_page_fault arch/x86/mm/fault.c:1475 [inline]
 exc_page_fault+0x94/0x230 arch/x86/mm/fault.c:1531
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1744 Comm: syz-fuzzer Tainted: G        W         5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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