perf/core: Verify we have a single perf_hw_context PMU

There should (and can) only be a single PMU for perf_hw_context
events.

This is because of how we schedule events: once a hardware event fails to
schedule (the PMU is 'full') we stop trying to add more. The trivial
'fix' would break the Round-Robin scheduling we do.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 52bedc5a5aaa190be3545d7534ce065ce735e473..525d11c59287b202c52e362842710d3b1cafb503 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7693,6 +7693,15 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type)
        }
 
 skip_type:
+       if (pmu->task_ctx_nr == perf_hw_context) {
+               static int hw_context_taken = 0;
+
+               if (WARN_ON_ONCE(hw_context_taken))
+                       pmu->task_ctx_nr = perf_invalid_context;
+
+               hw_context_taken = 1;
+       }
+
        pmu->pmu_cpu_context = find_pmu_context(pmu->task_ctx_nr);
        if (pmu->pmu_cpu_context)
                goto got_cpu_context;