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BUG: KCSAN: data-race in ext4_ext_try_to_merge_right / ext4_mark_iloc_dirty

write to 0xffff88813ac9a4b0 of 2 bytes by task 24 on cpu 1:
 ext4_ext_try_to_merge_right+0x285/0x4c0 fs/ext4/extents.c:1768
 ext4_ext_try_to_merge+0x6b/0x310 fs/ext4/extents.c:1852
 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 0xffff88813ac9a4b0 of 4 bytes by task 20655 on cpu 0:
 ext4_do_update_inode fs/ext4/inode.c:5111 [inline]
 ext4_mark_iloc_dirty+0xcf9/0x1700 fs/ext4/inode.c:5726
 __ext4_mark_inode_dirty+0x4db/0x5e0 fs/ext4/inode.c:5920
 ext4_dirty_inode+0x86/0xa0 fs/ext4/inode.c:5949
 __mark_inode_dirty+0x72/0x6f0 fs/fs-writeback.c:2274
 generic_update_time fs/inode.c:1766 [inline]
 update_time fs/inode.c:1779 [inline]
 touch_atime+0x1b3/0x2d0 fs/inode.c:1850
 file_accessed include/linux/fs.h:2319 [inline]
 filemap_read+0x74f/0x7b0 mm/filemap.c:2530
 generic_file_read_iter+0x82/0x410 mm/filemap.c:2609
 ext4_file_read_iter+0x2e0/0x420 fs/ext4/file.c:74
 call_read_iter include/linux/fs.h:1971 [inline]
 generic_file_splice_read+0x22a/0x310 fs/splice.c:311
 do_splice_to fs/splice.c:796 [inline]
 splice_direct_to_actor+0x2aa/0x650 fs/splice.c:870
 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:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 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: 20655 Comm: syz-executor.2 Not tainted 5.12.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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