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BUG: KCSAN: data-race in ext4_ext_insert_extent / ext4_mark_iloc_dirty

write to 0xffff88810dce964a of 2 bytes by task 640 on cpu 1:
 ext4_ext_store_pblock fs/ext4/ext4_extents.h:256 [inline]
 ext4_ext_insert_extent+0x1242/0x2bc0 fs/ext4/extents.c:2116
 ext4_ext_map_blocks+0x1597/0x1fd0 fs/ext4/extents.c:4259
 ext4_map_blocks+0x726/0xff0 fs/ext4/inode.c:638
 mpage_map_one_extent+0x10d/0x3a0 fs/ext4/inode.c:2397
 mpage_map_and_submit_extent fs/ext4/inode.c:2450 [inline]
 ext4_writepages+0xa51/0x1e70 fs/ext4/inode.c:2802
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __writeback_single_inode+0x80/0x4d0 fs/fs-writeback.c:1467
 writeback_sb_inodes+0x6a7/0xff0 fs/fs-writeback.c:1732
 wb_writeback+0x27d/0x660 fs/fs-writeback.c:1905
 wb_do_writeback+0x101/0x5d0 fs/fs-writeback.c:2050
 wb_workfn+0xc8/0x430 fs/fs-writeback.c:2091
 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 0xffff88810dce9648 of 4 bytes by task 11195 on cpu 0:
 ext4_do_update_inode fs/ext4/inode.c:5111 [inline]
 ext4_mark_iloc_dirty+0xd9c/0x16f0 fs/ext4/inode.c:5724
 __ext4_mark_inode_dirty+0x4db/0x5e0 fs/ext4/inode.c:5918
 ext4_dirty_inode+0x86/0xa0 fs/ext4/inode.c:5947
 __mark_inode_dirty+0x72/0x6f0 fs/fs-writeback.c:2274
 mark_inode_dirty include/linux/fs.h:2267 [inline]
 generic_write_end+0x166/0x240 fs/buffer.c:2203
 ext4_da_write_end+0x59b/0x760 fs/ext4/inode.c:3112
 generic_perform_write+0x23e/0x3a0 mm/filemap.c:3586
 ext4_buffered_write_iter+0x2e5/0x3e0 fs/ext4/file.c:269
 ext4_file_write_iter+0x48a/0x10b0 fs/ext4/file.c:502
 call_write_iter include/linux/fs.h:1977 [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
 ovl_write_iter+0x62f/0x8f0 fs/overlayfs/file.c:358
 call_write_iter include/linux/fs.h:1977 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x6f9/0x7e0 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+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11195 Comm: syz-executor.3 Not tainted 5.12.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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