• Lorenzo Pieralisi's avatar
    drivers/perf: arm-pmu: fix RCU usage on pmu resume from low-power · cbcc72e0
    Lorenzo Pieralisi authored
    Commit da4e4f18 ("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
    [   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>]
    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: da4e4f18 ("drivers/perf: arm_pmu: implement CPU_PM notifier")
    Signed-off-by: default avatarLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
    Reported-by: default avatarJames Morse <james.morse@arm.com>
    Suggested-by: default avatarKevin 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: default avatarMark Rutland <mark.rutland@arm.com>
    Acked-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Acked-by: default avatarWill Deacon <will.deacon@arm.com>
    Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
arm_pmu.c 24.8 KB