On Tue, 28 Aug 2018 15:00:14 +0000 Matteo Croce <mcr...@redhat.com> wrote:
> On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npig...@gmail.com> wrote: > > > > On Tue, 28 Aug 2018 12:54:08 +0000 > > Matteo Croce <mcr...@redhat.com> wrote: > > > > > With kernel 4.19.0-rc1 virtio_console hangs very often. > > > I can always trigger the bug by pasting some characters in the > > > terminal window, the console will stop receiving keypresses, but I can > > > still see output from the console. > > > Stangely, logging in the VM via SSH and sending lot of data to hvc0, > > > like 'dmesg >/dev/hvc0' will fix the issue until the next paste. > > > > > > I did a git bisect and I've found that this is the offending commit, > > > reverting it fixes it. > > > > > > Cheers, > > > > > > commit ec97eaad1383ab2500fcf9a07ade6044fbcc67f5 > > > Author: Nicholas Piggin <npig...@gmail.com> > > > Date: Tue May 1 00:55:54 2018 +1000 > > > > > > tty: hvc: hvc_poll() break hv read loop > > > > Thanks for the report. I can't immediately see what the problem > > is. Can you try get a stack trace of where it is stuck? > > > > I tried but didn't get one. > > > Perhaps try this patch if you have time (it's a bit of a shot > > in the dark). > > > > Yes it seems to fix. Thanks! Okay sorry for the delay, I can reproduce it here and found a better fix, if I could trouble you to test again. [PATCH] tty: hvc: hvc_poll() fix read loop hang Patch ec97eaad1383 ("tty: hvc: hvc_poll() break hv read loop") causes the virtio console to hang if you paste a bunch of characters to it. The reason is that get_chars must return 0 before we can be sure the driver will kick or poll input again, but this patch only scheduled a poll if get_chars had returned a full count. Change this to poll on > 0 count. Fixes: ec97eaad1383 ("tty: hvc: hvc_poll() break hv read loop") Reported-by: Matteo Croce <mcr...@redhat.com> Signed-off-by: Nicholas Piggin <npig...@gmail.com> --- drivers/tty/hvc/hvc_console.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c index 5414c4a87bea..219369aebb1f 100644 --- a/drivers/tty/hvc/hvc_console.c +++ b/drivers/tty/hvc/hvc_console.c @@ -717,10 +717,13 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep) #endif /* CONFIG_MAGIC_SYSRQ */ tty_insert_flip_char(&hp->port, buf[i], 0); } - if (n == count) - poll_mask |= HVC_POLL_READ; read_total = n; + /* Activity is occurring, so reset the polling backoff value to + a minimum for performance. */ + timeout = MIN_TIMEOUT; + poll_mask |= HVC_POLL_READ; + out: /* Wakeup write queue if necessary */ if (hp->do_wakeup) { @@ -730,13 +733,8 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep) bail: spin_unlock_irqrestore(&hp->lock, flags); - if (read_total) { - /* Activity is occurring, so reset the polling backoff value to - a minimum for performance. */ - timeout = MIN_TIMEOUT; - + if (read_total) tty_flip_buffer_push(&hp->port); - } tty_kref_put(tty); return poll_mask; -- 2.18.0