perf/x86/intel: Drop get_online_cpus() in intel_snb_check_microcode()

If intel_snb_check_microcode() is invoked via
  microcode_init -> perf_check_microcode -> intel_snb_check_microcode

then get_online_cpus() is invoked nested. This works with the current
implementation of get_online_cpus() but prevents converting it to a percpu
rwsem.

intel_snb_check_microcode() is also invoked from intel_sandybridge_quirk()
unprotected.

Drop get_online_cpus() from intel_snb_check_microcode() and add it to
intel_sandybridge_quirk() so both call sites are protected.

Convert *_online_cpus() to the new interfaces while at it.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov <bp@suse.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Borislav Petkov <bp@alien8.de>
Link: http://lkml.kernel.org/r/20170524081548.594862191@linutronix.de

1 files changed, 5 insertions, 6 deletions

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index a6d91d4e37a1..b9174aacf42f 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3410,12 +3410,10 @@ static void intel_snb_check_microcode(void)
         int pebs_broken = 0;
         int cpu;
 
-        get_online_cpus();
         for_each_online_cpu(cpu) {
                 if ((pebs_broken = intel_snb_pebs_broken(cpu)))
                         break;
         }
-        put_online_cpus();
 
         if (pebs_broken == x86_pmu.pebs_broken)
                 return;
@@ -3488,7 +3486,9 @@ static bool check_msr(unsigned long msr, u64 mask)
 static __init void intel_sandybridge_quirk(void)
 {
         x86_pmu.check_microcode = intel_snb_check_microcode;
+        cpus_read_lock();
         intel_snb_check_microcode();
+        cpus_read_unlock();
 }
 
 static const struct { int id; char *name; } intel_arch_events_map[] __initconst = {
@@ -4112,13 +4112,12 @@ static __init int fixup_ht_bug(void)
 
         lockup_detector_resume();
 
-        get_online_cpus();
+        cpus_read_lock();
 
-        for_each_online_cpu(c) {
+        for_each_online_cpu(c)
                 free_excl_cntrs(c);
-        }
 
-        put_online_cpus();
+        cpus_read_unlock();
         pr_info("PMU erratum BJ122, BV98, HSD29 workaround disabled, HT off\n");
         return 0;
 }