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 <[email protected]>
> ---
> 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
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