On Thu, Jun 05, 2014 at 05:01:25PM +0300, Maria Dimakopoulou wrote:
> On Thu, Jun 5, 2014 at 4:48 PM, Peter Zijlstra <pet...@infradead.org> wrote:
> > On Wed, Jun 04, 2014 at 11:34:14PM +0200, Stephane Eranian wrote:
> >
> >> +static struct event_constraint *
> >> +intel_get_excl_constraints(struct cpu_hw_events *cpuc, struct perf_event
> >> *event,
> >> + struct event_constraint *c)
> >> +{
> >
> >> + if (!(c->flags & PERF_X86_EVENT_DYNAMIC)) {
> >> +
> >> + /*
> >> + * in case we fail, we assume no counter
> >> + * is supported to be on the safe side
> >> + */
> >> + cx = kmalloc(sizeof(*cx), GFP_KERNEL);
> >> + if (!cx)
> >> + return &emptyconstraint;
> >> +
> >
> > Ok, so forgive me if I'm wrong, but the way we get here is through:
> >
> > x86_schedule_event()
> > ->start_scheduling()
> > spin_lock()
> > ->get_event_constraints()
> > intel_get_excl_constraints()
> > kmalloc(.gfp=GFP_KERNEL)
> >
> > How can that ever work?> Are you saying it is illegal to call kmalloc() from > this context? Nobody will come and arrest you for it, so no. Broken though. GFP_KERNEL will attempt to sleep to wait for reclaim, and you're holding a spinlock. > kmalloc is needed because we need to allocate > a new constraint struct since the static constraint > cannot be modified. > > Worst case we can statically allocate a second > constraint struct in the event struct. Nah, since you will need at most one constraint per counter, you could preallocate num_counter constraints for each cpu.
pgpQbUsOGTHpk.pgp
Description: PGP signature
