[PATCH] perf,x86: fix uninitialized pt_regs in intel_pmu_drain_bts_buffer()

[Stephane Eranian <eranian@google.com>]

This patch fixes an uninitialized pt_regs struct in drain BTS
function. The pt_regs struct is propagated all the way to the
code_get_segment() function from perf_instruction_pointer()
and may get garbage.

We cannot simply inherit the actual pt_regs from the interrupt
because BTS must be flushed on context-switch or when the associated
event is disabled. And there we do not have a pt_regs handy.

Setting pt_regs to all zeroes may not be the best option but it is
not clear what else to do given where the drain_bts_buffer() is called
from.

Signed-off-by: Stephane Eranian <eranian@google.com>
---

diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
index b05a575..208f0c8 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
@@ -302,6 +302,8 @@ int intel_pmu_drain_bts_buffer(void)
 	struct perf_sample_data data;
 	struct pt_regs regs;
 
+	memset(&regs, 0, sizeof(regs));
+
 	if (!event)
 		return 0;