[PATCH kernel] powerpc/perf: Stop crashing with generic_compat_pmu

[Alexey Kardashevskiy]

The bhrb_filter_map ("The  Branch  History  Rolling  Buffer") callback is
only defined in raw CPUs' power_pmu structs. The "architected" CPUs use
generic_compat_pmu which does not have this callback and crashed occur.

This add a NULL pointer check for bhrb_filter_map() which behaves as if
the callback returned an error.

This does not add the same check for config_bhrb() as the only caller
checks for cpuhw->bhrb_users which remains zero if bhrb_filter_map==0.

Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
---
 arch/powerpc/perf/core-book3s.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 3dcfecf858f3..36870569bf9c 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1515,9 +1515,16 @@ static int power_pmu_add(struct perf_event *event, int 
ef_flags)
        ret = 0;
  out:
        if (has_branch_stack(event)) {
-               power_pmu_bhrb_enable(event);
-               cpuhw->bhrb_filter = ppmu->bhrb_filter_map(
-                                       event->attr.branch_sample_type);
+               u64 bhrb_filter = -1;
+
+               if (ppmu->bhrb_filter_map)
+                       bhrb_filter = ppmu->bhrb_filter_map(
+                               event->attr.branch_sample_type);
+
+               if (bhrb_filter != -1) {
+                       cpuhw->bhrb_filter = bhrb_filter;
+                       power_pmu_bhrb_enable(event); /* Does bhrb_users++ */
+               }
        }
 
        perf_pmu_enable(event->pmu);
@@ -1839,7 +1846,6 @@ static int power_pmu_event_init(struct perf_event *event)
        int n;
        int err;
        struct cpu_hw_events *cpuhw;
-       u64 bhrb_filter;
 
        if (!ppmu)
                return -ENOENT;
@@ -1945,7 +1951,10 @@ static int power_pmu_event_init(struct perf_event *event)
        err = power_check_constraints(cpuhw, events, cflags, n + 1);
 
        if (has_branch_stack(event)) {
-               bhrb_filter = ppmu->bhrb_filter_map(
+               u64 bhrb_filter = -1;
+
+               if (ppmu->bhrb_filter_map)
+                       bhrb_filter = ppmu->bhrb_filter_map(
                                        event->attr.branch_sample_type);
 
                if (bhrb_filter == -1) {
-- 
2.17.1