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BUG: KCSAN: data-race in ext4_ext_insert_extent / ext4_mark_iloc_dirty

write to 0xffff888028456a38 of 4 bytes by task 21 on cpu 0:
 ext4_ext_store_pblock fs/ext4/ext4_extents.h:255 [inline]
 ext4_ext_insert_extent+0x19d5/0x2b50 fs/ext4/extents.c:2116
 ext4_ext_map_blocks+0x1629/0x1fa0 fs/ext4/extents.c:4261
 ext4_map_blocks+0x71b/0xfc0 fs/ext4/inode.c:626
 mpage_map_one_extent+0x10d/0x390 fs/ext4/inode.c:2385
 mpage_map_and_submit_extent fs/ext4/inode.c:2438 [inline]
 ext4_writepages+0xa2c/0x1e10 fs/ext4/inode.c:2790
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __writeback_single_inode+0x84/0x560 fs/fs-writeback.c:1461
 writeback_sb_inodes+0x6a0/0x1020 fs/fs-writeback.c:1721
 wb_writeback+0x27d/0x660 fs/fs-writeback.c:1894
 wb_do_writeback+0x101/0x5d0 fs/fs-writeback.c:2039
 wb_workfn+0xb8/0x410 fs/fs-writeback.c:2080
 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 0xffff888028456a38 of 4 bytes by task 3383 on cpu 1:
 ext4_do_update_inode fs/ext4/inode.c:5104 [inline]
 ext4_mark_iloc_dirty+0xe3a/0x1650 fs/ext4/inode.c:5711
 __ext4_mark_inode_dirty+0x450/0x610 fs/ext4/inode.c:5905
 ext4_dirty_inode+0xa6/0xc0 fs/ext4/inode.c:5941
 __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:3322
 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]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x617/0x690 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 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: 1 PID: 3383 Comm: syz-executor.3 Not tainted 5.10.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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