Re: [PATCH v1 2/2] x86, perf,cqm: handle CPU hotplug

Thomas Gleixner
2015-06-18T19:47:48Z

On Thu, 18 Jun 2015, Kanaka Juvva wrote:

> Added lock in event reader function. The cqm_pick_event_reader() function
> accesses cqm_cpumask and it is critical section between this and
> cqm_stable().
>
> This situation is true when a CPU is hotplugged. Mutex is used to protect
> the critical section.
>
> Signed-off-by: Kanaka Juvva <kanaka.d.juvva@linux.intel.com>
> ---
> arch/x86/kernel/cpu/perf_event_intel_cqm.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
> index 1880761..e17e37f 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
> @@ -1239,12 +1239,15 @@ static inline void cqm_pick_event_reader(int cpu)
> int phys_id = topology_physical_package_id(cpu);
> int i;
>
> + mutex_lock(&cache_mutex);

I already explained it to Vikas. You CANNOT take a mutex in that code
path as it runs with interrupts disabled on a CPU which cannot
schedule.

Sigh.

tglx