2024-04-15 07:26:32

by li.hao40

Subject: [PATCH v2] tty: hvc: wakeup hvc console immediately when needed

From: Li Hao <[email protected]>

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.

v1->v2:
Some fixes according to:
https://lore.kernel.org/all/[email protected]/
use tty_port_tty_wakeup() instead of tty_wakeup() to wake up tty

Signed-off-by: Li Hao <[email protected]>
---
drivers/tty/hvc/hvc_console.c | 10 +++-------
drivers/tty/hvc/hvc_console.h | 1 -
2 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index cd1f657f7..cbd234847 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -480,7 +480,7 @@ static int hvc_push(struct hvc_struct *hp)
n = hp->ops->put_chars(hp->vtermno, hp->outbuf, hp->n_outbuf);
if (n <= 0) {
if (n == 0 || n == -EAGAIN) {
- hp->do_wakeup = 1;
+ tty_port_tty_wakeup(&hp->port);
return 0;
}
/* throw away output on error; this happens when
@@ -491,7 +491,7 @@ static int hvc_push(struct hvc_struct *hp)
if (hp->n_outbuf > 0)
memmove(hp->outbuf, hp->outbuf + n, hp->n_outbuf);
else
- hp->do_wakeup = 1;
+ tty_port_tty_wakeup(&hp->port);

return n;
}
@@ -739,11 +739,7 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep)
poll_mask |= HVC_POLL_READ;

out:
- /* Wakeup write queue if necessary */
- if (hp->do_wakeup) {
- hp->do_wakeup = 0;
- tty_wakeup(tty);
- }
+ /* Wakeup in hvc_push */
bail:
spin_unlock_irqrestore(&hp->lock, flags);

diff --git a/drivers/tty/hvc/hvc_console.h b/drivers/tty/hvc/hvc_console.h
index cf4c1af08..6622f71ba 100644
--- a/drivers/tty/hvc/hvc_console.h
+++ b/drivers/tty/hvc/hvc_console.h
@@ -36,7 +36,6 @@ struct hvc_struct {
struct tty_port port;
spinlock_t lock;
int index;
- int do_wakeup;
int outbuf_size;
int n_outbuf;
uint32_t vtermno;
--
2.25.1

2024-04-15 07:33:44

by Greg Kroah-Hartman

Subject: Re: [PATCH v2] tty: hvc: wakeup hvc console immediately when needed

On Mon, Apr 15, 2024 at 03:26:17PM +0800, [email protected] wrote:
> From: Li Hao <[email protected]>
>
> 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.
>
> v1->v2:
> Some fixes according to:
> https://lore.kernel.org/all/[email protected]/
> use tty_port_tty_wakeup() instead of tty_wakeup() to wake up tty

As per the documentation, the v1... stuff needs to go below the --- line
so git will strip it away.

Please fix up and send a v3.

thanks,

greg k-h