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Date: Fri, 12 Apr 2024 08:51:43 +0200
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Subject: Re: [PATCH] tty: hvc: wakeup hvc console immediately when needed
To: li.hao40@zte.com.cn
Cc: gregkh@linuxfoundation.org, linuxppc-dev@lists.ozlabs.org,
 linux-kernel@vger.kernel.org
References: <20240412113848167egmP7kBg1Qm5sxfwGALG-@zte.com.cn>
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From: Jiri Slaby <jirislaby@kernel.org>
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On 12. 04. 24, 5:38, li.hao40@zte.com.cn wrote:
> From: Li Hao <li.hao40@zte.com.cn>
> 
> Cancel the do_wakeup flag in hvc_struct, and change it to immediately
> wake up tty when hp->n_outbuf is 0 in hvc_push().
> 
> When we receive a key input character, the interrupt handling function
> hvc_handle_interrupt() will be executed, and the echo thread
> flush_to_ldisc() will be added to the queue.
> 
> If the user is currently using tcsetattr(), a hang may occur. tcsetattr()
> enters kernel and waits for hp->n_outbuf to become 0 via
> tty_wait_until_sent(). If the echo thread finishes executing before
> reaching tty_wait_until_sent (for example, put_chars() takes too long),
> it will cause while meeting the wakeup condition (hp->do_wakeup = 1),
> tty_wait_until_sent() cannot be woken up (missed the tty_wakeup() of
> this round's tty_poll). Unless the next key input character comes,
> hvc_poll will be executed, and tty_wakeup() will be performed through
> the do_wakeup flag.
> 
> Signed-off-by: Li Hao <li.hao40@zte.com.cn>
> ---
>   drivers/tty/hvc/hvc_console.c | 12 +++++-------
>   drivers/tty/hvc/hvc_console.h |  1 -
>   2 files changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
> index cd1f657f7..2fa90d938 100644
> --- a/drivers/tty/hvc/hvc_console.c
> +++ b/drivers/tty/hvc/hvc_console.c
> @@ -476,11 +476,13 @@ static void hvc_hangup(struct tty_struct *tty)
>   static int hvc_push(struct hvc_struct *hp)
>   {
>   	int n;
> +	struct tty_struct *tty;
> 
>   	n = hp->ops->put_chars(hp->vtermno, hp->outbuf, hp->n_outbuf);
> +	tty = tty_port_tty_get(&hp->port);
>   	if (n <= 0) {
>   		if (n == 0 || n == -EAGAIN) {
> -			hp->do_wakeup = 1;
> +			tty_wakeup(tty);

What if tty is NULL? Did you intent to use tty_port_tty_wakeup() instead?

thanks,
-- 
js
suse labs