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Subject[tip:smp/hotplug] perf/x86/intel: Drop get_online_cpus() in intel_snb_check_microcode()
Commit-ID:  494d8679788930b29e1262d92db4c1912bdf9119
Gitweb: http://git.kernel.org/tip/494d8679788930b29e1262d92db4c1912bdf9119
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate: Tue, 18 Apr 2017 19:04:58 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 20 Apr 2017 13:08:55 +0200

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.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Borislav Petkov <bp@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Borislav Petkov <bp@alien8.de>
Link: http://lkml.kernel.org/r/20170418170553.713742599@linutronix.de

---
arch/x86/events/intel/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index eb1484c..152b7e4 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3389,12 +3389,10 @@ 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;
@@ -3467,7 +3465,9 @@ static bool check_msr(unsigned long msr, u64 mask)
static __init void intel_sandybridge_quirk(void)
{
x86_pmu.check_microcode = intel_snb_check_microcode;
+ get_online_cpus();
intel_snb_check_microcode();
+ put_online_cpus();
}

static const struct { int id; char *name; } intel_arch_events_map[] __initconst = {
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