Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH v2] perf/arm-dmc620: Reverse locking order in dmc620_pmu_get_irq() | Date | Mon, 10 Jul 2023 14:19:59 -0400 |
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The following circular locking dependency was reported when running cpus online/offline test on an arm64 system.
[ 84.195923] Chain exists of: dmc620_pmu_irqs_lock --> cpu_hotplug_lock --> cpuhp_state-down
[ 84.207305] Possible unsafe locking scenario:
[ 84.213212] CPU0 CPU1 [ 84.217729] ---- ---- [ 84.222247] lock(cpuhp_state-down); [ 84.225899] lock(cpu_hotplug_lock); [ 84.232068] lock(cpuhp_state-down); [ 84.238237] lock(dmc620_pmu_irqs_lock); [ 84.242236] *** DEADLOCK ***
The problematic locking order seems to be
lock(dmc620_pmu_irqs_lock) --> lock(cpu_hotplug_lock)
This locking order happens when dmc620_pmu_get_irq() is called from dmc620_pmu_device_probe(). Since dmc620_pmu_irqs_lock is used for protecting the dmc620_pmu_irqs structure only, we don't actually need to hold the lock when adding a new instance to the CPU hotplug subsystem.
Fix this possible deadlock scenario by releasing the lock when a new dmc620_pmu_irq needs to be created and reacquring it again when the new irq is inserted into dmc620_pmu_irqs.
Suggested-by: Robin Murphy <robin.murphy@arm.com> Signed-off-by: Waiman Long <longman@redhat.com> --- drivers/perf/arm_dmc620_pmu.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/drivers/perf/arm_dmc620_pmu.c b/drivers/perf/arm_dmc620_pmu.c index 9d0f01c4455a..dbf67c122420 100644 --- a/drivers/perf/arm_dmc620_pmu.c +++ b/drivers/perf/arm_dmc620_pmu.c @@ -419,13 +419,16 @@ static irqreturn_t dmc620_pmu_handle_irq(int irq_num, void *data) } static struct dmc620_pmu_irq *__dmc620_pmu_get_irq(int irq_num) + __releases(&dmc620_pmu_irqs_lock) { struct dmc620_pmu_irq *irq; int ret; list_for_each_entry(irq, &dmc620_pmu_irqs, irqs_node) if (irq->irq_num == irq_num && refcount_inc_not_zero(&irq->refcount)) - return irq; + goto out_unlock; + + mutex_unlock(&dmc620_pmu_irqs_lock); irq = kzalloc(sizeof(*irq), GFP_KERNEL); if (!irq) @@ -452,8 +455,12 @@ static struct dmc620_pmu_irq *__dmc620_pmu_get_irq(int irq_num) goto out_free_irq; irq->irq_num = irq_num; + + mutex_lock(&dmc620_pmu_irqs_lock); list_add(&irq->irqs_node, &dmc620_pmu_irqs); +out_unlock: + mutex_unlock(&dmc620_pmu_irqs_lock); return irq; out_free_irq: @@ -469,7 +476,7 @@ static int dmc620_pmu_get_irq(struct dmc620_pmu *dmc620_pmu, int irq_num) mutex_lock(&dmc620_pmu_irqs_lock); irq = __dmc620_pmu_get_irq(irq_num); - mutex_unlock(&dmc620_pmu_irqs_lock); + /* mutex_unlock() called inside __dmc620_pmu_get_irq() */ if (IS_ERR(irq)) return PTR_ERR(irq); -- 2.31.1
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