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

[Alexey Kardashevskiy]

On 03/12/2020 16:27, Madhavan Srinivasan wrote:

On 12/2/20 8:31 AM, Alexey Kardashevskiy wrote:

Hi Maddy,

I just noticed that I still have "powerpc/perf: Add checks for reserved values" in my pile (pushed here https://github.com/aik/linux/commit/61e1bc3f2e19d450e2e2d39174d422160b21957b ), do we still need it? The lockups I saw were fixed by https://github.com/aik/linux/commit/17899eaf88d689 but it is hardly a replacement. Thanks,

sorry missed this. Will look at this again. Since we will need generation specific checks for the reserve field.

So any luck with this? Cheers,

Maddy

On 04/06/2020 02:34, Madhavan Srinivasan wrote:

On 6/2/20 8:26 AM, Alexey Kardashevskiy wrote:

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.

Changes looks fine.
Reviewed-by: Madhavan Srinivasan <ma...@linux.ibm.com>

The commit be80e758d0c2e ('powerpc/perf: Add generic compat mode pmu driver')

which introduced generic_compat_pmu was merged in v5.2.  So we need to
CC stable starting from 5.2 :( .  My bad,  sorry.

Maddy

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) {

--
Alexey