VirtIO console hangs

VirtIO console hangs

[Matteo Croce]

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 <npiggin@gmail.com>
Date:   Tue May 1 00:55:54 2018 +1000

    tty: hvc: hvc_poll() break hv read loop

    Avoid looping with the spinlock held while there is read data
    being returned from the hv driver. Instead note if the entire
    size returned by tty_buffer_request_room was read, and request
    another read poll.

    This limits the critical section lengths, and provides more
    even service to other consoles in case there is a pathological
    condition.

    Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
-- 
Matteo Croce
per aspera ad upstream

Re: VirtIO console hangs

[Nicholas Piggin]

On Tue, 28 Aug 2018 12:54:08 +0000
Matteo Croce <mcroce@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 <npiggin@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?

Perhaps try this patch if you have time (it's a bit of a shot
in the dark).

Thanks,
Nick

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 5414c4a87bea..ac45235832f1 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -635,6 +635,7 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep)
 	int read_total = 0;
 	int written_total = 0;
 
+again:
 	spin_lock_irqsave(&hp->lock, flags);
 
 	/* Push pending writes */
@@ -721,6 +722,10 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep)
 		poll_mask |= HVC_POLL_READ;
 	read_total = n;
 
+	spin_unlock_irqrestore(&hp->lock, flags);
+	cond_resched();
+	goto again;
+
  out:
 	/* Wakeup write queue if necessary */
 	if (hp->do_wakeup) {

Re: VirtIO console hangs

[Matteo Croce]

On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npiggin@gmail.com> wrote:
>
> On Tue, 28 Aug 2018 12:54:08 +0000
> Matteo Croce <mcroce@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 <npiggin@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!

-- 
Matteo Croce
per aspera ad upstream

Re: VirtIO console hangs

[Nicholas Piggin]

On Tue, 28 Aug 2018 15:00:14 +0000
Matteo Croce <mcroce@redhat.com> wrote:

> On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npiggin@gmail.com> wrote:
> >
> > On Tue, 28 Aug 2018 12:54:08 +0000
> > Matteo Croce <mcroce@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 <npiggin@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!

Great thanks for testing it so quickly.

I would have thought the return code should cause another poll to
trigger. I'll have to read the code again and try to find out what
I missed.

Thanks,
Nick

Re: VirtIO console hangs

[Nicholas Piggin]

On Tue, 28 Aug 2018 15:00:14 +0000
Matteo Croce <mcroce@redhat.com> wrote:

> On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npiggin@gmail.com> wrote:
> >
> > On Tue, 28 Aug 2018 12:54:08 +0000
> > Matteo Croce <mcroce@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 <npiggin@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 <mcroce@redhat.com>
Signed-off-by: Nicholas Piggin <npiggin@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

Re: VirtIO console hangs

[Matteo Croce]

On Fri, Aug 31, 2018 at 3:49 AM Nicholas Piggin <npiggin@gmail.com> wrote:
>
> On Tue, 28 Aug 2018 15:00:14 +0000
> Matteo Croce <mcroce@redhat.com> wrote:
>
> > On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npiggin@gmail.com> wrote:
> > >
> > > On Tue, 28 Aug 2018 12:54:08 +0000
> > > Matteo Croce <mcroce@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 <npiggin@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
>

Hi Nicholas,

the patch works, but now pasting text inside the terminal is extremely
slow, it feels worse than a 9600 baud serial line.

Btw, I had to apply the patch by hand as it was corrupted, some lines
were collapsed into one.

Cheers,
-- 
Matteo Croce
per aspera ad upstream

Re: VirtIO console hangs

[Nicholas Piggin]

On Fri, 31 Aug 2018 15:17:44 +0000
Matteo Croce <mcroce@redhat.com> wrote:

> On Fri, Aug 31, 2018 at 3:49 AM Nicholas Piggin <npiggin@gmail.com> wrote:
> >
> > On Tue, 28 Aug 2018 15:00:14 +0000
> > Matteo Croce <mcroce@redhat.com> wrote:
> >  
> > > On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npiggin@gmail.com> wrote:  
> > > >
> > > > On Tue, 28 Aug 2018 12:54:08 +0000
> > > > Matteo Croce <mcroce@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 <npiggin@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
> >  
> 
> Hi Nicholas,
> 
> the patch works, but now pasting text inside the terminal is extremely
> slow, it feels worse than a 9600 baud serial line.
> 
> Btw, I had to apply the patch by hand as it was corrupted, some lines
> were collapsed into one.

Okay I didn't test a very big paste, I'll work on it.

Thanks,
Nick

Re: VirtIO console hangs

[Nicholas Piggin]

On Fri, 31 Aug 2018 15:17:44 +0000
Matteo Croce <mcroce@redhat.com> wrote:

> On Fri, Aug 31, 2018 at 3:49 AM Nicholas Piggin <npiggin@gmail.com> wrote:
> >
> > On Tue, 28 Aug 2018 15:00:14 +0000
> > Matteo Croce <mcroce@redhat.com> wrote:
> >  
> > > On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npiggin@gmail.com> wrote:  
> > > >
> > > > On Tue, 28 Aug 2018 12:54:08 +0000
> > > > Matteo Croce <mcroce@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 <npiggin@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
> >  
> 
> Hi Nicholas,
> 
> the patch works, but now pasting text inside the terminal is extremely
> slow, it feels worse than a 9600 baud serial line.
> 
> Btw, I had to apply the patch by hand as it was corrupted, some lines
> were collapsed into one.

Oh, when you revert the above commit, does it fix the speed problem as
well? I realise I'm testing with a remote machine that probably is not
connected with much better than 9600 baud... I will set up a local test.

Thanks,
Nick

Re: VirtIO console hangs

[Nicholas Piggin]

On Fri, 31 Aug 2018 15:17:44 +0000
Matteo Croce <mcroce@redhat.com> wrote:

> On Fri, Aug 31, 2018 at 3:49 AM Nicholas Piggin <npiggin@gmail.com> wrote:
> >
> > On Tue, 28 Aug 2018 15:00:14 +0000
> > Matteo Croce <mcroce@redhat.com> wrote:
> >  
> > > On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npiggin@gmail.com> wrote:  
> > > >
> > > > On Tue, 28 Aug 2018 12:54:08 +0000
> > > > Matteo Croce <mcroce@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 <npiggin@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
> >  
> 
> Hi Nicholas,
> 
> the patch works, but now pasting text inside the terminal is extremely
> slow, it feels worse than a 9600 baud serial line.
> 
> Btw, I had to apply the patch by hand as it was corrupted, some lines
> were collapsed into one.

Not sure why that happened, I seem to be able to send myself
uncorrupted patches...

Can you try this patch for performance? Hopefully it applies.
--

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 5414c4a87bea..f5fc3ba49130 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -49,6 +49,8 @@
 #define N_OUTBUF	16
 #define N_INBUF		16
 
+#define HVC_ATOMIC_READ_MAX	128
+
 #define __ALIGNED__ __attribute__((__aligned__(sizeof(long))))
 
 static struct tty_driver *hvc_driver;
@@ -522,6 +524,8 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count
 		return -EIO;
 
 	while (count > 0) {
+		int ret;
+
 		spin_lock_irqsave(&hp->lock, flags);
 
 		rsize = hp->outbuf_size - hp->n_outbuf;
@@ -537,10 +541,13 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count
 		}
 
 		if (hp->n_outbuf > 0)
-			hvc_push(hp);
+			ret = hvc_push(hp);
 
 		spin_unlock_irqrestore(&hp->lock, flags);
 
+		if (!ret)
+			break;
+
 		if (count) {
 			if (hp->n_outbuf > 0)
 				hvc_flush(hp);
@@ -669,8 +676,8 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep)
 	if (!hp->irq_requested)
 		poll_mask |= HVC_POLL_READ;
 
+ read_again:
 	/* Read data if any */
-
 	count = tty_buffer_request_room(&hp->port, N_INBUF);
 
 	/* If flip is full, just reschedule a later read */
@@ -717,9 +724,23 @@ 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;
+	read_total += n;
+
+	if (may_sleep) {
+		/* Keep going until the flip is full */
+		spin_unlock_irqrestore(&hp->lock, flags);
+		cond_resched();
+		spin_lock_irqsave(&hp->lock, flags);
+		goto read_again;
+	} else if (read_total < HVC_ATOMIC_READ_MAX) {
+		/* Break and defer if it's a large read in atomic */
+		goto read_again;
+	}
+
+	/*
+	 * Latency break, schedule another poll immediately.
+	 */
+	poll_mask |= HVC_POLL_READ;
 
  out:
 	/* Wakeup write queue if necessary */

Re: VirtIO console hangs

[Matteo Croce]

On Wed, Sep 5, 2018 at 3:54 AM Nicholas Piggin <npiggin@gmail.com> wrote:
>
> On Fri, 31 Aug 2018 15:17:44 +0000
> Matteo Croce <mcroce@redhat.com> wrote:
>
> > On Fri, Aug 31, 2018 at 3:49 AM Nicholas Piggin <npiggin@gmail.com> wrote:
> > >
> > > On Tue, 28 Aug 2018 15:00:14 +0000
> > > Matteo Croce <mcroce@redhat.com> wrote:
> > >
> > > > On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npiggin@gmail.com> wrote:
> > > > >
> > > > > On Tue, 28 Aug 2018 12:54:08 +0000
> > > > > Matteo Croce <mcroce@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 <npiggin@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
> > >
> >
> > Hi Nicholas,
> >
> > the patch works, but now pasting text inside the terminal is extremely
> > slow, it feels worse than a 9600 baud serial line.
> >
> > Btw, I had to apply the patch by hand as it was corrupted, some lines
> > were collapsed into one.
>
> Not sure why that happened, I seem to be able to send myself
> uncorrupted patches...
>
> Can you try this patch for performance? Hopefully it applies.

Hi Nicholas,

This one works really well, as in kernel 4.17.
Feel free to add me in Tested-by or Reported-by (or both).

Cheers,
--
Matteo Croce
per aspera ad upstream