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SubjectRe: [RFC PATCH v2 0/3] genirq, serial: 8250: Workaround to avoid irq=0 for console
On Wed, 29 Jul 2015, Peter Hurley wrote:
> On 07/29/2015 07:53 AM, Thomas Gleixner wrote:
> > On Wed, 29 Jul 2015, Peter Hurley wrote:
> >> On 07/29/2015 06:32 AM, Thomas Gleixner wrote:
> >>> On Wed, 29 Jul 2015, Taichi Kageyama wrote:
> >>>> - Keep interrupt disabled on the CPU which is used to detect
> >>>> an interrupt during the timeout of autoconfig_irq().
> >>>> + Kick printk() on the CPU which detects interrupt
> >>>> from a console serial port.
> >>>
> >>> This is wrong to begin with. How is that supposed to work on an UP
> >>> machine? Not at all.
> >>>
> >>> So no, fix the code which has interrupts disabled accross autoprobing
> >>> and do not try to apply bandaids somewhere else.
> >>
> >> Like printk() from some unrelated driver?
> >
> > If that's the cause for the wreckage then yes, we need a way to tell
> > the printk code not to call into the driver until that initialization
> > step is done. It's that simple.
>
> Like this?

Looks about right.

> --- >% --
> Subject: [PATCH] genirq: Disable printk() during irq probe
>
> printk() disables interrupts for extended periods of time while
> outputting to console drivers. This breaks irq probing since the
> triggered irq may not be serviced (in time) if scheduled on the
> printk() cpu.
>
> Claim the console_lock() which effectively disables console output.
>
> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
> ---
> kernel/irq/autoprobe.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/kernel/irq/autoprobe.c b/kernel/irq/autoprobe.c
> index 0119b9d..47535d2 100644
> --- a/kernel/irq/autoprobe.c
> +++ b/kernel/irq/autoprobe.c
> @@ -39,6 +39,13 @@ unsigned long probe_irq_on(void)
> */
> async_synchronize_full();
> mutex_lock(&probing_active);
> +
> + /*
> + * printk() breaks irq probing - disable printk output until probe
> + * completes
> + */
> + console_lock();
> +
> /*
> * something may have generated an irq long ago and we want to
> * flush such a longstanding irq before considering it as spurious.
> @@ -132,6 +139,7 @@ unsigned int probe_irq_mask(unsigned long val)
> }
> raw_spin_unlock_irq(&desc->lock);
> }
> + console_unlock();
> mutex_unlock(&probing_active);
>
> return mask & val;
> @@ -174,6 +182,7 @@ int probe_irq_off(unsigned long val)
> }
> raw_spin_unlock_irq(&desc->lock);
> }
> + console_unlock();
> mutex_unlock(&probing_active);
>
> if (nr_of_irqs > 1)
> --
> 2.5.0
>
>


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