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BUG: KCSAN: data-race in ext4_ext_try_to_merge / ext4_mark_iloc_dirty

write to 0xffff8881301d3924 of 2 bytes by task 19456 on cpu 1:
 ext4_ext_try_to_merge_up fs/ext4/extents.c:1827 [inline]
 ext4_ext_try_to_merge+0x2af/0x310 fs/ext4/extents.c:1857
 ext4_convert_unwritten_extents_endio fs/ext4/extents.c:3721 [inline]
 ext4_ext_handle_unwritten_extents+0x67a/0xaa0 fs/ext4/extents.c:3849
 ext4_ext_map_blocks+0x719/0x1f00 fs/ext4/extents.c:4119
 ext4_map_blocks+0x70d/0xef0 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+0x3e9/0x8f0 kernel/workqueue.c:2275
 worker_thread+0x636/0xae0 kernel/workqueue.c:2421
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8881301d3924 of 4 bytes by task 22339 on cpu 0:
 ext4_do_update_inode fs/ext4/inode.c:5109 [inline]
 ext4_mark_iloc_dirty+0xcc1/0x1750 fs/ext4/inode.c:5724
 __ext4_mark_inode_dirty+0x4db/0x5b0 fs/ext4/inode.c:5918
 ext4_dirty_inode+0x86/0xa0 fs/ext4/inode.c:5947
 __mark_inode_dirty+0x77/0x6c0 fs/fs-writeback.c:2274
 mark_inode_dirty include/linux/fs.h:2404 [inline]
 generic_write_end+0x157/0x180 fs/buffer.c:2223
 ext4_da_write_end+0x59b/0x730 fs/ext4/inode.c:3110
 generic_perform_write+0x23e/0x3a0 mm/filemap.c:3671
 ext4_buffered_write_iter+0x2f2/0x3f0 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:519
 call_write_iter include/linux/fs.h:2114 [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+0x773/0xda0 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 22339 Comm: syz-executor.5 Tainted: G        W         5.13.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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