On Thu, Jun 22, 2017 at 03:41:38PM +0100, Mark Rutland wrote: > Regardless of which events form a group, it does not make sense for the > events to target different tasks and/or CPUs, as this leaves the group > inconsistent and impossible to schedule. The core perf code assumes that > these are consistent across (successfully intialised) groups. > > Core perf code only verifies this when moving SW events into a HW > context. Thus, we can violate this requirement for pure SW groups and > pure HW groups, unless the relevant PMU driver happens to perform this > verification itself. These mismatched groups subsequently wreak havoc > elsewhere. > > For example, we handle watchpoints as SW events, and reserve watchpoint > HW on a per-cpu basis at pmu::event_init() time to ensure that any event > that is initialised is guaranteed to have a slot at pmu::add() time. > However, the core code only checks the group leader's cpu filter (via > event_filter_match()), and can thus install follower events onto CPUs > violating thier (mismatched) CPU filters, potentially installing them > into a CPU without sufficient reserved slots. >
> > Fix this by validating this requirement regardless of whether we're > moving events. Yes, and this also appears to cure your other problem: https://lkml.kernel.org/r/20170810173551.GD12812@leverpostej Thanks!
