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Date: Fri, 12 Apr 2024 15:48:06 +0800 (CST)
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From: <li.hao40@zte.com.cn>
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        <linux-kernel@vger.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

Thank you for your prompt reply.
tty_port_tty_wakeup() is better, it no longer check if tty is NULL in hvc_push()

Li Hao