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BUG: KCSAN: data-race in ext4_ext_handle_unwritten_extents / ext4_mark_iloc_dirty

write to 0xffff88811ed35728 of 2 bytes by task 3606 on cpu 1:
 ext4_ext_mark_initialized fs/ext4/ext4_extents.h:218 [inline]
 ext4_convert_unwritten_extents_endio fs/ext4/extents.c:3721 [inline]
 ext4_ext_handle_unwritten_extents+0x609/0xaa0 fs/ext4/extents.c:3854
 ext4_ext_map_blocks+0x758/0x20c0 fs/ext4/extents.c:4124
 ext4_map_blocks+0x6d3/0xf60 fs/ext4/inode.c:626
 ext4_convert_unwritten_extents+0x16a/0x2d0 fs/ext4/extents.c:4755
 ext4_convert_unwritten_io_end_vec+0xa4/0x130 fs/ext4/extents.c:4794
 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+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

read to 0xffff88811ed35728 of 4 bytes by task 15694 on cpu 0:
 ext4_do_update_inode fs/ext4/inode.c:5042 [inline]
 ext4_mark_iloc_dirty+0xdcf/0x1660 fs/ext4/inode.c:5624
 __ext4_mark_inode_dirty+0x448/0x630 fs/ext4/inode.c:5818
 ext4_dirty_inode+0xa6/0xc0 fs/ext4/inode.c:5854
 __mark_inode_dirty+0x72/0x7e0 fs/fs-writeback.c:2258
 generic_update_time fs/inode.c:1762 [inline]
 update_time fs/inode.c:1775 [inline]
 touch_atime+0x157/0x1a0 fs/inode.c:1846
 file_accessed include/linux/fs.h:2229 [inline]
 generic_file_buffered_read+0x1918/0x19e0 mm/filemap.c:2249
 generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2326
 ext4_file_read_iter+0x2d6/0x420 fs/ext4/file.c:74
 call_read_iter include/linux/fs.h:1902 [inline]
 generic_file_splice_read+0x22a/0x310 fs/splice.c:312
 do_splice_to fs/splice.c:870 [inline]
 splice_direct_to_actor+0x2a8/0x660 fs/splice.c:950
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x562/0xb10 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1601 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15694 Comm: syz-executor.2 Not tainted 5.8.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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