On Wed, 2017-10-04 at 06:50:52 UTC, Anju T Sudhakar wrote: > Nest/core pmu units are enabled only when it is used. A reference count is > > maintained for the events which uses the nest/core pmu units. Currently in > > *_imc_counters_release function a WARN() is used for notification of any > > underflow of ref count. > > > > The case where event ref count hit a negative value is, when perf session is > > started, followed by offlining of all cpus in a given core. > > i.e. in cpuhotplug offline path ppc_core_imc_cpu_offline() function set the > > ref->count to zero, if the current cpu which is about to offline is the last > > cpu in a given core and make an OPAL call to disable the engine in that core. > > And on perf session termination, perf->destroy (core_imc_counters_release) > will > first decrement the ref->count for this core and based on the ref->count > value > an opal call is made to disable the core-imc engine. > > Now, since cpuhotplug path already clears the ref->count for core and > disabled > the engine, perf->destroy() decrementing again at event termination make it > > negative which in turn fires the WARN_ON. The same happens for nest units. > > > > Add a check to see if the reference count is alreday zero, before > decrementing > the count, so that the ref count will not hit a negative value. > > > > Signed-off-by: Anju T Sudhakar <a...@linux.vnet.ibm.com> > Reviewed-by: Santosh Sivaraj <sant...@fossix.org>
Applied to powerpc fixes, thanks. https://git.kernel.org/powerpc/c/0d923820c6db1644c27c2d0a5af892 cheers
