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Date:   Sat, 19 Dec 2020 08:50:47 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     zhangqiumiao1@...ei.com
Cc:     jirislaby@...nel.org, linux-kernel@...r.kernel.org,
        zhangqiumiao <zhangqiumiao1@...wei.com>
Subject: Re: [PATCH] tty: fix timeout equals to 0 problem in tty_ioctl

On Sat, Dec 19, 2020 at 11:27:31AM +0800, zhangqiumiao1@...ei.com wrote:
> From: zhangqiumiao <zhangqiumiao1@...wei.com>
> 
> Fix the problem that tty buffer data was not flushed when timeout=0.
> 
> Signed-off-by: zhangqiumiao <zhangqiumiao1@...wei.com>
> ---
>  drivers/tty/tty_ioctl.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
> index 4de1c6ddb8ff..f9d4b6e22308 100644
> --- a/drivers/tty/tty_ioctl.c
> +++ b/drivers/tty/tty_ioctl.c
> @@ -220,13 +220,21 @@ void tty_wait_until_sent(struct tty_struct *tty, long timeout)
>  	tty_debug_wait_until_sent(tty, "wait until sent, timeout=%ld\n", timeout);
>  
>  	if (!timeout)
> -		timeout = MAX_SCHEDULE_TIMEOUT;
> +		timeout = 60 * HZ;

Why change this?

>  
>  	timeout = wait_event_interruptible_timeout(tty->write_wait,
>  			!tty_chars_in_buffer(tty), timeout);
> -	if (timeout <= 0)
> +	if (timeout < 0)
>  		return;

How can timeout be 0 here?

> +	if (timeout == 0) {
> +		if (tty->ops->flush_buffer) {
> +			pr_info("%s: flush buffer\n", __func__);

Debugging code?

> +			tty->ops->flush_buffer(tty);
> +		}
> +		return;
> +	}
> +

thanks,

greg k-h

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