Re: + drivers-wait-for-threaded-probes-between-initcall-levels.patch added to -mm tree

Re: + drivers-wait-for-threaded-probes-between-initcall-levels.patch added to -mm tree

[Cornelia Huck]

On Wed, 25 Oct 2006 19:12:01 -0700,
akpm@osdl.org wrote:

> Subject: drivers: wait for threaded probes between initcall levels
> From: Andrew Morton <akpm@osdl.org>
> 
> The multithreaded-probing code has a problem: after one initcall level (eg,
> core_initcall) has been processed, we will then start processing the next
> level (postcore_initcall) while the kernel threads which are handling
> core_initcall are still executing.  This breaks the guarantees which the
> layered initcalls previously gave us.
> 
> IOW, we want to be multithreaded _within_ an initcall level, but not between
> different levels.
> 
> Fix that up by causing the probing code to wait for all outstanding probes at
> one level to complete before we start processing the next level.
> 
> Cc: Greg KH <greg@kroah.com>
> Signed-off-by: Andrew Morton <akpm@osdl.org>

Makes a lot of sense. I guess we could also get rid of
driver_probe_done() in prepare_namespace() with this patch...


> +#ifdef CONFIG_PCI_MULTITHREAD_PROBE
> +static int __init wait_for_probes(void)
> +{
> +	DEFINE_WAIT(wait);
> +
> +	if (!atomic_read(&probe_count))
> +		return 0;
> +	printk(KERN_INFO "%s: waiting for %d threads\n", __FUNCTION__,
> +			atomic_read(&probe_count));
> +	while (atomic_read(&probe_count)) {
> +		prepare_to_wait(&probe_waitqueue, &wait, TASK_UNINTERRUPTIBLE);
> +		if (atomic_read(&probe_count))
> +			schedule();
> +	}
> +	finish_wait(&probe_waitqueue, &wait);
> +	return 0;
> +}
> +
> +core_initcall_sync(wait_for_probes);
> +postcore_initcall_sync(wait_for_probes);
> +arch_initcall_sync(wait_for_probes);
> +subsys_initcall_sync(wait_for_probes);
> +fs_initcall_sync(wait_for_probes);
> +device_initcall_sync(wait_for_probes);
> +late_initcall_sync(wait_for_probes);
> +#endif

...if we get rid of this #ifdef.

-- 
Cornelia Huck
Linux for zSeries Developer
Tel.: +49-7031-16-4837, Mail: cornelia.huck@de.ibm.com

Re: + drivers-wait-for-threaded-probes-between-initcall-levels.patch added to -mm tree

[Greg KH]

On Thu, Oct 26, 2006 at 10:09:39AM +0200, Cornelia Huck wrote:
> On Wed, 25 Oct 2006 19:12:01 -0700,
> akpm@osdl.org wrote:
> 
> > Subject: drivers: wait for threaded probes between initcall levels
> > From: Andrew Morton <akpm@osdl.org>
> > 
> > The multithreaded-probing code has a problem: after one initcall level (eg,
> > core_initcall) has been processed, we will then start processing the next
> > level (postcore_initcall) while the kernel threads which are handling
> > core_initcall are still executing.  This breaks the guarantees which the
> > layered initcalls previously gave us.
> > 
> > IOW, we want to be multithreaded _within_ an initcall level, but not between
> > different levels.
> > 
> > Fix that up by causing the probing code to wait for all outstanding probes at
> > one level to complete before we start processing the next level.
> > 
> > Cc: Greg KH <greg@kroah.com>
> > Signed-off-by: Andrew Morton <akpm@osdl.org>
> 
> Makes a lot of sense. I guess we could also get rid of
> driver_probe_done() in prepare_namespace() with this patch...
> 
> 
> > +#ifdef CONFIG_PCI_MULTITHREAD_PROBE
> > +static int __init wait_for_probes(void)
> > +{
> > +	DEFINE_WAIT(wait);
> > +
> > +	if (!atomic_read(&probe_count))
> > +		return 0;
> > +	printk(KERN_INFO "%s: waiting for %d threads\n", __FUNCTION__,
> > +			atomic_read(&probe_count));
> > +	while (atomic_read(&probe_count)) {
> > +		prepare_to_wait(&probe_waitqueue, &wait, TASK_UNINTERRUPTIBLE);
> > +		if (atomic_read(&probe_count))
> > +			schedule();
> > +	}
> > +	finish_wait(&probe_waitqueue, &wait);
> > +	return 0;
> > +}
> > +
> > +core_initcall_sync(wait_for_probes);
> > +postcore_initcall_sync(wait_for_probes);
> > +arch_initcall_sync(wait_for_probes);
> > +subsys_initcall_sync(wait_for_probes);
> > +fs_initcall_sync(wait_for_probes);
> > +device_initcall_sync(wait_for_probes);
> > +late_initcall_sync(wait_for_probes);
> > +#endif
> 
> ...if we get rid of this #ifdef.

Yeah, let me play with this a bit, along with your proposed change, I
think it can be cleaned up to be a little more cleaner.

thanks,

greg k-h