sparc64: Fix pcr_ops initialization and usage bugs.

Christopher reports that perf_event_print_debug() can crash in uniprocessor
builds.  The crash is due to pcr_ops being NULL.

This happens because pcr_arch_init() is only invoked by smp_cpus_done() which
only executes in SMP builds.

init_hw_perf_events() is closely intertwined with pcr_ops being setup properly,
therefore:

1) Call pcr_arch_init() early on from init_hw_perf_events(), instead of
   from smp_cpus_done().

2) Do not hook up a PMU type if pcr_ops is NULL after pcr_arch_init().

3) Move init_hw_perf_events to a later initcall so that it we will be
   sure to invoke pcr_arch_init() after all cpus are brought up.

Finally, guard the one naked sequence of pcr_ops dereferences in
__global_pmu_self() with an appropriate NULL check.

Reported-by: Christopher Alexander Tobias Schulze <cat.schulze@alice-dsl.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 8 insertions, 3 deletions

diff --git a/arch/sparc/kernel/perf_event.c b/arch/sparc/kernel/perf_event.c
index 8efd33753ad3..d35c490a91cb 100644
--- a/arch/sparc/kernel/perf_event.c
+++ b/arch/sparc/kernel/perf_event.c
@@ -1671,9 +1671,12 @@ static bool __init supported_pmu(void)
 
 static int __init init_hw_perf_events(void)
 {
+        int err;
+
         pr_info("Performance events: ");
 
-        if (!supported_pmu()) {
+        err = pcr_arch_init();
+        if (err || !supported_pmu()) {
                 pr_cont("No support for PMU type '%s'\n", sparc_pmu_type);
                 return 0;
         }
@@ -1685,7 +1688,7 @@ static int __init init_hw_perf_events(void)
 
         return 0;
 }
-early_initcall(init_hw_perf_events);
+pure_initcall(init_hw_perf_events);
 
 void perf_callchain_kernel(struct perf_callchain_entry *entry,
                            struct pt_regs *regs)
diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
index 027e09986194..0be7bf978cb1 100644
--- a/arch/sparc/kernel/process_64.c
+++ b/arch/sparc/kernel/process_64.c
@@ -312,6 +312,9 @@ static void __global_pmu_self(int this_cpu)
         struct global_pmu_snapshot *pp;
         int i, num;
 
+        if (!pcr_ops)
+                return;
+
         pp = &global_cpu_snapshot[this_cpu].pmu;
 
         num = 1;
diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c
index 41aa2478f3ca..f7ba87543e5f 100644
--- a/arch/sparc/kernel/smp_64.c
+++ b/arch/sparc/kernel/smp_64.c
@@ -1383,7 +1383,6 @@ void __cpu_die(unsigned int cpu)
 
 void __init smp_cpus_done(unsigned int max_cpus)
 {
-        pcr_arch_init();
 }
 
 void smp_send_reschedule(int cpu)