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BUG: KCSAN: data-race in ext4_set_iomap / writeback_single_inode

write to 0xffff8880bb742648 of 8 bytes by task 18548 on cpu 1:
 writeback_single_inode+0x104/0x530 fs/fs-writeback.c:1562
 sync_inode fs/fs-writeback.c:2602 [inline]
 sync_inode_metadata+0x52/0x70 fs/fs-writeback.c:2622
 ext4_fsync_nojournal fs/ext4/fsync.c:92 [inline]
 ext4_sync_file+0x335/0x6e0 fs/ext4/fsync.c:170
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2744 [inline]
 iomap_dio_complete+0x2de/0x380 fs/iomap/direct-io.c:126
 iomap_dio_rw+0x873/0x980 fs/iomap/direct-io.c:577
 ext4_dio_write_iter fs/ext4/file.c:548 [inline]
 ext4_file_write_iter+0xdd5/0x1060 fs/ext4/file.c:658
 call_write_iter include/linux/fs.h:1882 [inline]
 new_sync_write fs/read_write.c:503 [inline]
 vfs_write+0x665/0x6f0 fs/read_write.c:578
 ksys_write+0xce/0x180 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write fs/read_write.c:640 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:640
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880bb742648 of 8 bytes by task 18553 on cpu 0:
 ext4_inode_datasync_dirty fs/ext4/inode.c:3305 [inline]
 ext4_set_iomap+0x138/0x3e0 fs/ext4/inode.c:3320
 ext4_iomap_begin_report+0x2f9/0x390 fs/ext4/inode.c:3567
 iomap_apply+0x8b/0x540 fs/iomap/apply.c:46
 iomap_fiemap+0x100/0x270 fs/iomap/fiemap.c:83
 ext4_fiemap+0x1ee/0x210 fs/ext4/extents.c:4904
 ioctl_fiemap fs/ioctl.c:216 [inline]
 do_vfs_ioctl+0x8e8/0xec0 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:751 [inline]
 __se_sys_ioctl+0x83/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 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: 18553 Comm: syz-executor.2 Not tainted 5.9.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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