linux-kernel - [tip:smp/hotplug] perf/x86/intel: Drop get_online_cpus() in intel_snb_check

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Message-ID: <tip-494d8679788930b29e1262d92db4c1912bdf9119@git.kernel.org>
Date:   Thu, 20 Apr 2017 04:26:29 -0700
From:   tip-bot for Sebastian Andrzej Siewior <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     bp@...e.de, tglx@...utronix.de, bigeasy@...utronix.de,
        linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
        peterz@...radead.org, bp@...en8.de, rostedt@...dmis.org
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@...utronix.de>
AuthorDate: Tue, 18 Apr 2017 19:04:58 +0200
Committer:  Thomas Gleixner <tglx@...utronix.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@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Borislav Petkov <bp@...e.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Borislav Petkov <bp@...en8.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 = {