From 25152dbcc1e5c0278670436e1f1e1f51320529c5 Mon Sep 17 00:00:00 2001 From: Lorenzo Pieralisi Date: Thu, 21 Apr 2016 10:24:34 +0100 Subject: [PATCH] UPSTREAM: drivers/perf: arm-pmu: fix RCU usage on pmu resume from low-power (cherry picked from cbcc72e037b8a3eb1fad3c1ae22021df21c97a51) 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: [] cpu_pm_exit+0x18/0x80 [ 49.355492] #1: (rcu_read_lock){......}, at: [] 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. Change-Id: I6352b3e7970a2116d23e258fa085f0c29982f789 Fixes: da4e4f18afe0 ("drivers/perf: arm_pmu: implement CPU_PM notifier") Signed-off-by: Lorenzo Pieralisi Reported-by: James Morse Suggested-by: Kevin Hilman Cc: Ashwin Chaugule Cc: Kevin Hilman Cc: Sudeep Holla Cc: Daniel Lezcano Cc: Mathieu Poirier Acked-by: Mark Rutland Acked-by: Paul E. McKenney Acked-by: Will Deacon Signed-off-by: Catalin Marinas --- drivers/perf/arm_pmu.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c index 85b445c50feeea..64b07b2d47f8a9 100644 --- a/drivers/perf/arm_pmu.c +++ b/drivers/perf/arm_pmu.c @@ -745,8 +745,19 @@ 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;