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BUG: KCSAN: data-race in ext4_mb_find_by_goal / mb_free_blocks

write to 0xffff8881416f20a4 of 4 bytes by task 19530 on cpu 1:
 mb_free_blocks+0x156/0xb60 fs/ext4/mballoc.c:1464
 ext4_free_blocks+0x135d/0x1be0 fs/ext4/mballoc.c:5456
 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:3721 [inline]
 ext4_ext_handle_unwritten_extents+0x670/0xac0 fs/ext4/extents.c:3849
 ext4_ext_map_blocks+0x728/0x1fd0 fs/ext4/extents.c:4119
 ext4_map_blocks+0x726/0xff0 fs/ext4/inode.c:638
 ext4_convert_unwritten_extents+0x15a/0x2c0 fs/ext4/extents.c:4760
 ext4_convert_unwritten_io_end_vec+0xa4/0x130 fs/ext4/extents.c:4799
 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+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8881416f20a4 of 4 bytes by task 19052 on cpu 0:
 ext4_mb_find_by_goal+0x129/0xb40 fs/ext4/mballoc.c:1866
 ext4_mb_regular_allocator+0x110/0x1900 fs/ext4/mballoc.c:2297
 ext4_mb_new_blocks+0x6f8/0x1150 fs/ext4/mballoc.c:4982
 ext4_ext_map_blocks+0x146f/0x1fd0 fs/ext4/extents.c:4238
 ext4_map_blocks+0x726/0xff0 fs/ext4/inode.c:638
 ext4_alloc_file_blocks+0x271/0x720 fs/ext4/extents.c:4425
 ext4_fallocate+0x2a7/0x540 fs/ext4/extents.c:4705
 vfs_fallocate+0x479/0x6d0 fs/open.c:311
 file_ioctl fs/ioctl.c:494 [inline]
 do_vfs_ioctl+0xdd4/0xec0 fs/ioctl.c:732
 __do_sys_ioctl fs/ioctl.c:751 [inline]
 __se_sys_ioctl+0x83/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 19052 Comm: syz-executor.2 Tainted: G        W         5.12.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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