Background node process corrupts terminal state with tcsetattr() on exit

• Version: v14.9.0
• Platform: NixOS 21.03, Linux 5.8.11 x86_64
• Subsystem: ResetStdio in src/node.cc

In Bash, run the following:

node -e 'setTimeout(() => {}, 2000)' & sleep 1

This launches node -e 'setTimeout(() => {}, 2000)' in the background and sleep 1 in the foreground. After 1 second, control returns to Bash. After 2 seconds, Node exits and corrupts Bash’s terminal state:

• the ↑, ↓, →, ← arrow keys start printing ^[[A, ^[[B, ^[[C, ^[[D instead of scrolling through the Bash history or moving the insert point,
• the Tab key starts moving the cursor 8 spaces forward instead of Tab-completing the command,
• Ctrl+A and Ctrl+E print ^A and ^E instead of jumping to the beginning and end of the command, etc.

This happens when the ResetStdio handler uses tcsetattr to “restore” the terminal to the state it was in when Node started (#24260). This interferes with Bash, which uses and expects a different terminal state than sleep 1.

(The bug is sometimes reproducible without the sleep 1 depending on whether Node records the initial terminal state before Bash updates it, but the sleep 1 makes it reliable.)

Normally, the terminal state would be protected from such undesired modifications by a background process: the kernel generates SIGTTOU to suspend the process until it’s brought to the foreground. But ResetStdio now deliberately overrides this protection by blocking SIGTTOU (#28535).

IMO, both #24260 and #28535 should be reverted. Node is a programming language; it should never make changes to the terminal state that programs did not request.

src/node.cc の ResetStdio ハンドラーから始め、報告にある Bash コマンドで問題を再現してください。SIGTTOU の処理と tcsetattr の呼び出しを含め、#24260 と #28535 のコンテキストを読んでください。バックグラウンドの Node プロセスが Bash の端末動作を変更せずに終了すれば完了です。