syzbot

==================================================================
BUG: KCSAN: data-race in __bforget / sync_mapping_buffers

write to 0xffff88800e6dc608 of 8 bytes by task 14400 on cpu 1:
 __remove_assoc_queue fs/buffer.c:481 [inline]
 fsync_buffers_list fs/buffer.c:752 [inline]
 sync_mapping_buffers+0x427/0x7e0 fs/buffer.c:548
 ext4_fsync_nojournal fs/ext4/fsync.c:86 [inline]
 ext4_sync_file+0x286/0x6e0 fs/ext4/fsync.c:170
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2843 [inline]
 ext4_buffered_write_iter+0x38f/0x3e0 fs/ext4/file.c:277
 ext4_file_write_iter+0x48a/0x10b0 fs/ext4/file.c:502
 call_write_iter include/linux/fs.h:1977 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4c0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x40a/0x750 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x7a6/0xe20 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1319 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1311
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88800e6dc608 of 8 bytes by task 201 on cpu 0:
 __bforget+0x22/0x120 fs/buffer.c:1188
 bforget include/linux/buffer_head.h:295 [inline]
 __ext4_forget+0x65/0x660 fs/ext4/ext4_jbd2.c:269
 ext4_free_blocks+0x704/0x1be0 fs/ext4/mballoc.c:5331
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 201 Comm: kworker/u4:3 Tainted: G        W         5.12.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
==================================================================
vhci_hcd: stop threads
vhci_hcd: release socket
vhci_hcd: disconnect device
vhci_hcd: stop threads
vhci_hcd: release socket
vhci_hcd: disconnect device
vhci_hcd: stop threads
vhci_hcd: release socket
vhci_hcd: disconnect device