Lorenzo Pieralisi cbcc72e037 drivers/perf: arm-pmu: fix RCU usage on pmu resume from low-power ... Commit da4e4f18af ("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: da4e4f18af ("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>		2016-04-21 15:03:06 +01:00
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arm_pmu.c	drivers/perf: arm-pmu: fix RCU usage on pmu resume from low-power	2016-04-21 15:03:06 +01:00
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