On Thu, Dec 2, 2021 at 7:41 AM Tetsuo Handa
<penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
Looking at the backtrace, I see
n_hdlc_send_frames+0x24b/0x490 drivers/tty/n_hdlc.c:290
tty_wakeup+0xe1/0x120 drivers/tty/tty_io.c:534
__start_tty drivers/tty/tty_io.c:806 [inline]
__start_tty+0xfb/0x130 drivers/tty/tty_io.c:799
and apparently it's that hdlc line discipline (and
n_hdlc_send_frames() in particular) that is the problem here.
I think that's where the fix should be.
Do you mean that we should change the behavior of n_hdlc_send_frames()
rather than trying to make __start_tty() schedulable again?
I wouldn't change n_hdlc_send_frames() itself. It does what it says it does.
But n_hdlc_tty_wakeup() probably shouldn't call it directly. Other tty
line disciplines don't do that kind of thing - although I only looked
at a couple. They all seem to just set bits and prepare things. Like a
wakeup function should do.
So I think n_hdlc_tty_wakeup() should perhaps only do a
"schedule_work()" or similar to get that n_hdlc_send_frames() started,
rather than doing it itself.