Consider a scenario where user creates two events:
1st event:
attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
attr.branch_sample_type = PERF_SAMPLE_BRANCH_ANY;
fd = perf_event_open(attr, 0, 1, -1, 0);
This sets cpuhw->bhrb_filter to 0 and returns valid fd.
2nd event:
attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
attr.branch_sample_type = PERF_SAMPLE_BRANCH_CALL;
fd = perf_event_open(attr, 0, 1, -1, 0);
It overrides cpuhw->bhrb_filter to -1 and returns with error.
Now if power_pmu_enable() gets called by any path other than
power_pmu_add(), ppmu->config_bhrb(-1) will set MMCRA to -1.
Fixes: 3925f46bb5 ("powerpc/perf: Enable branch stack sampling framework")
Cc: stable@vger.kernel.org # v3.10+
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Reviewed-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
3202e35ec1