Messages in this thread | | | Subject | Re: [patch 6/7] cpusets: per cpuset dirty ratios | From | Peter Zijlstra <> | Date | Thu, 30 Oct 2008 10:34:16 +0100 |
| |
On Thu, 2008-10-30 at 02:03 -0700, David Rientjes wrote: > On Thu, 30 Oct 2008, Peter Zijlstra wrote: > > > On Tue, 2008-10-28 at 09:08 -0700, David Rientjes wrote: > > > > > +/* > > > + * Determine the dirty ratios for the currently active cpuset > > > + */ > > > +void cpuset_get_current_dirty_ratios(int *background, int *throttle) > > > +{ > > > + mutex_lock(&callback_mutex); > > > + task_lock(current); > > > + *background = task_cs(current)->dirty_background_ratio; > > > + *throttle = task_cs(current)->cpuset_dirty_ratio; > > > + task_unlock(current); > > > + mutex_unlock(&callback_mutex); > > > + > > > + if (*background == -1) > > > + *background = dirty_background_ratio; > > > + if (*throttle == -1) > > > + *throttle = vm_dirty_ratio; > > > +} > > > > That's rather an awful lot of locking to read just two integers. > > > > As far as I know, task_lock(current) is required to dereference > task_cs(current) and callback_mutex is required to ensure its the same > cpuset.
Since we read these things for every evaluation, getting it wrong isn't too harmful.
So I would suggest just enough locking to ensure we don't reference any NULL pointers and such.
IIRC the cpuset stuff is RCU freed, so some racy read should be possible, no?
| |