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BUG: KCSAN: data-race in ext4_ext_try_to_merge_right / ext4_mark_iloc_dirty

write to 0xffff888138853a42 of 2 bytes by task 20 on cpu 1:
 le16_add_cpu include/linux/byteorder/generic.h:146 [inline]
 ext4_ext_try_to_merge_right+0x34f/0x4c0 fs/ext4/extents.c:1777
 ext4_ext_try_to_merge+0x6b/0x310 fs/ext4/extents.c:1851
 ext4_convert_unwritten_extents_endio fs/ext4/extents.c:3720 [inline]
 ext4_ext_handle_unwritten_extents+0x5fd/0xaf0 fs/ext4/extents.c:3850
 ext4_ext_map_blocks+0x764/0x1fd0 fs/ext4/extents.c:4120
 ext4_map_blocks+0x71b/0xfc0 fs/ext4/inode.c:626
 ext4_convert_unwritten_extents+0x15a/0x2c0 fs/ext4/extents.c:4765
 ext4_convert_unwritten_io_end_vec+0xa4/0x130 fs/ext4/extents.c:4804
 ext4_end_io_end fs/ext4/page-io.c:187 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:260 [inline]
 ext4_end_io_rsv_work+0x198/0x360 fs/ext4/page-io.c:274
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
 worker_thread+0x635/0xb90 kernel/workqueue.c:2418
 kthread+0x1fa/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff888138853a40 of 4 bytes by task 19355 on cpu 0:
 ext4_do_update_inode fs/ext4/inode.c:5102 [inline]
 ext4_mark_iloc_dirty+0xcc0/0x1650 fs/ext4/inode.c:5709
 __ext4_mark_inode_dirty+0x450/0x610 fs/ext4/inode.c:5903
 ext4_dirty_inode+0xa6/0xc0 fs/ext4/inode.c:5939
 __mark_inode_dirty+0x74/0x740 fs/fs-writeback.c:2260
 mark_inode_dirty include/linux/fs.h:2167 [inline]
 generic_write_end+0x15e/0x250 fs/buffer.c:2202
 ext4_da_write_end+0x59b/0x760 fs/ext4/inode.c:3100
 generic_perform_write+0x23e/0x3a0 mm/filemap.c:3544
 ext4_buffered_write_iter+0x2e5/0x3d0 fs/ext4/file.c:270
 ext4_file_write_iter+0x45e/0x1090 fs/ext4/file.c:503
 call_write_iter include/linux/fs.h:1887 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4b0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x42a/0x780 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:933
 splice_direct_to_actor+0x345/0x650 fs/splice.c:888
 do_splice_direct+0xf5/0x170 fs/splice.c:976
 do_sendfile+0x574/0xb70 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1318 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1304
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 19355 Comm: syz-executor.2 Not tainted 5.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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