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authorLorenzo Pieralisi <lorenzo.pieralisi@arm.com>2016-04-21 12:24:34 +0300
committerCatalin Marinas <catalin.marinas@arm.com>2016-04-21 17:03:06 +0300
commitcbcc72e037b8a3eb1fad3c1ae22021df21c97a51 (patch)
tree1f410947f90887d88c43dd614a07bb5c4ff7b1c9
parent2fee7d5b08b6419bb59de9e875d895e3a6e7bf5a (diff)
downloadlinux-cbcc72e037b8a3eb1fad3c1ae22021df21c97a51.tar.xz
drivers/perf: arm-pmu: fix RCU usage on pmu resume from low-power
Commit da4e4f18afe0 ("drivers/perf: arm_pmu: implement CPU_PM notifier") added code in the arm perf infrastructure that allows the kernel to save/restore perf counters whenever the CPU enters a low-power state. The kernel saves/restores the counters for each active event through the armpmu_{stop/start} ARM pmu API, so that the low-power state enter/exit cycle is emulated through pmu start/stop operations for each event in use. However, calling armpmu_start() for each active event on power up executes code that requires RCU locking (perf_event_update_userpage()) to be functional, so, given that the core may call the CPU_PM notifiers while running the idle thread in an quiescent RCU state this is not allowed as detected through the following splat when kernel is run with CONFIG_PROVE_LOCKING enabled: [ 49.293286] [ 49.294761] =============================== [ 49.298895] [ INFO: suspicious RCU usage. ] [ 49.303031] 4.6.0-rc3+ #421 Not tainted [ 49.306821] ------------------------------- [ 49.310956] include/linux/rcupdate.h:872 rcu_read_lock() used illegally while idle! [ 49.318530] [ 49.318530] other info that might help us debug this: [ 49.318530] [ 49.326451] [ 49.326451] RCU used illegally from idle CPU! [ 49.326451] rcu_scheduler_active = 1, debug_locks = 0 [ 49.337209] RCU used illegally from extended quiescent state! [ 49.342892] 2 locks held by swapper/2/0: [ 49.346768] #0: (cpu_pm_notifier_lock){......}, at: [<ffffff8008163c28>] cpu_pm_exit+0x18/0x80 [ 49.355492] #1: (rcu_read_lock){......}, at: [<ffffff800816dc38>] perf_event_update_userpage+0x0/0x260 This patch wraps the armpmu_start() call (that indirectly calls perf_event_update_userpage()) on CPU_PM notifier power state exit (or failed entry) within the RCU_NONIDLE() macro so that the RCU subsystem is made aware the calling cpu is not idle from an RCU perspective for the armpmu_start() call duration, therefore fixing the issue. Fixes: da4e4f18afe0 ("drivers/perf: arm_pmu: implement CPU_PM notifier") Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> Reported-by: James Morse <james.morse@arm.com> Suggested-by: Kevin Hilman <khilman@baylibre.com> Cc: Ashwin Chaugule <ashwin.chaugule@linaro.org> Cc: Kevin Hilman <khilman@baylibre.com> Cc: Sudeep Holla <sudeep.holla@arm.com> Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Mathieu Poirier <mathieu.poirier@linaro.org> Acked-by: Mark Rutland <mark.rutland@arm.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
-rw-r--r--drivers/perf/arm_pmu.c15
1 files changed, 13 insertions, 2 deletions
diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 32346b5a8a11..f70090897fdf 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -737,8 +737,19 @@ static void cpu_pm_pmu_setup(struct arm_pmu *armpmu, unsigned long cmd)
break;
case CPU_PM_EXIT:
case CPU_PM_ENTER_FAILED:
- /* Restore and enable the counter */
- armpmu_start(event, PERF_EF_RELOAD);
+ /*
+ * Restore and enable the counter.
+ * armpmu_start() indirectly calls
+ *
+ * perf_event_update_userpage()
+ *
+ * that requires RCU read locking to be functional,
+ * wrap the call within RCU_NONIDLE to make the
+ * RCU subsystem aware this cpu is not idle from
+ * an RCU perspective for the armpmu_start() call
+ * duration.
+ */
+ RCU_NONIDLE(armpmu_start(event, PERF_EF_RELOAD));
break;
default:
break;