Re: q-tools OOPS: Fixed perfmon.

[Stephane Eranian <eranian@hpl.hp.com>]

Peter,

On Mon, Dec 08, 2003 at 05:57:04PM -0800, Stephane Eranian wrote:
> 
> Yes, clearly you do not want to preempt in the perfmon interrupt handler.
> I think we need to also make sure we do not preempt during the perfmonctl()
> system call, at least until we verify that there is no assumptions in there.
> Similarly in all the VFS entry points, such as pfm_close(). I will try
> and see what I can do before the end of the week.
> 
I checked the code and I believe we are covered because we rely upon
spin_lock_irqsave/restore for most entry points into perfmon-2. That
is enough to block/unblock preemption in all the calls that need it.
That applies to the sys_perfmonctl() entry, the VFS entry points
as well as the internal entry points for copy_threads() and a few others.
The only one missing is the one you found. The PMU state save/restore
are called from the scheduler and are therefore protected as well.

Thanks for tracking down that one bug.

-- 

-Stephane