linux-kernel - Re: [PATCH] tty/hvc/hvc_console: Fix wakeup of HVC thread on hvc

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Date:	Wed, 28 May 2014 10:01:30 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linuxppc-dev list <linuxppc-dev@...abs.org>
Subject: Re: [PATCH] tty/hvc/hvc_console: Fix wakeup of HVC thread on
 hvc_kick()

On Fri, 2014-05-23 at 19:41 +1000, Benjamin Herrenschmidt wrote:
> Some backends call hvc_kick() to wakeup the HVC thread from its
> slumber upon incoming characters. This however doesn't work
> properly because it uses msleep_interruptible() which is mostly
> immune to wake_up_process(). It will basically go back to sleep
> until the timeout is expired (only signals can really wake it).
>
> Replace it with a simple shedule_timeout_interruptible() instead,
> which may wakeup earlier every now and then but we really don't
> care in this case.

Nobody commented ? :-)

Greg, do you want to take this in the tty tree or can I stick it in
powerpc ?

Cheers,
Ben 

> Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> ---
>  drivers/tty/hvc/hvc_console.c |    9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
> index 94f9e3a..1094265 100644
> --- a/drivers/tty/hvc/hvc_console.c
> +++ b/drivers/tty/hvc/hvc_console.c
> @@ -760,10 +760,17 @@ static int khvcd(void *unused)
>  			if (poll_mask == 0)
>  				schedule();
>  			else {
> +				unsigned long j_timeout;
> +
>  				if (timeout < MAX_TIMEOUT)
>  					timeout += (timeout >> 6) + 1;
>  
> -				msleep_interruptible(timeout);
> +				/*
> +				 * We don't use msleep_interruptible otherwise
> +				 * "kick" will fail to wake us up
> +				 */
> +				j_timeout = msecs_to_jiffies(timeout) + 1;
> +				schedule_timeout_interruptible(j_timeout);
>  			}
>  		}
>  		__set_current_state(TASK_RUNNING);
> 


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