Re: 2.6.14-git3: scheduling while atomic from cpufreq on Athlon64

[Rafael J. Wysocki]

Hi,

On Monday, 31 of October 2005 21:42, Ashok Raj wrote:
> On Mon, Oct 31, 2005 at 08:45:32PM +0100, Rafael J. Wysocki wrote:
> > On Monday, 31 of October 2005 20:34, Andrew Morton wrote:
> > > "Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
> > }-- snip --{
> > > > scheduling while atomic: swapper/0x00000001/1
> > > > 
> > > > Call Trace:<ffffffff8035014a>{schedule+122} <ffffffff802e2453>{cpufreq_frequency_table_target+371}
> > > >        <ffffffff8011d60c>{powernowk8_target+1916} <ffffffff802dfdb4>{__cpufreq_driver_target+116}
> > > >        <ffffffff801be269>{sysfs_new_dirent+41} <ffffffff802e097e>{cpufreq_governor_performance+62}
> > > >        <ffffffff802dec8d>{__cpufreq_governor+173} <ffffffff802df417>{__cpufreq_set_policy+551}
> > > >        <ffffffff802df5bf>{cpufreq_set_policy+79} <ffffffff802df946>{cpufreq_add_dev+806}
> > > >        <ffffffff802df540>{handle_update+0} <ffffffff802ae21a>{sysdev_driver_register+170}
> > > >        <ffffffff802df106>{cpufreq_register_driver+198} <ffffffff8010c122>{init+194}
> > > >        <ffffffff8010f556>{child_rip+8} <ffffffff8010c060>{init+0}
> > > >        <ffffffff8010f54e>{child_rip+0} 
> > > 
> > > Well I can't find it.  Ingo, didn't you have a debug patch which would help
> > > us identify where this atomic section started?
> > 
> > This is 100% reproducible on my box so I'll try to figure out what's up tomorrow
> > (unless someone else does it earlier ;-)).  Now I can only say it did not happen
> > with 2.6.14-rc5-mm1.
> 
> This could be because of the new patch, i added preempt_disable() instead
> of taking cpucontrol lock in __cpufreq_driver_target().

Yes, that's it.

> The reason is we now enter the same code path from the cpu_up() and cpu_down()
> generated cpu notifier callbacks and ends up trying to lock when the 
> call path already has the cpucontrol lock.
> 
> Its happening because we do set_cpus_allowed() in powernowk8_target().

Unfortunately, powernowk8_target() calls schedule() right after
set_cpus_allowed(), so it throws "scheduling while atomic" on every call,
because of the preempt_disable()/_enable() around it.

Greetings,
Rafael

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