Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH v3] perf/arm-dmc620: Fix dmc620_pmu_irqs_lock/cpu_hotplug_lock circular lock dependency | Date | Fri, 21 Jul 2023 23:17:28 -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 before calling cpuhp_state_add_instance_nocalls() and reacquiring it afterward. To avoid the possibility of 2 racing dmc620_pmu_get_irq() calls inserting duplicated dmc620_pmu_irq structures with the same irq number, a dummy entry is inserted before releasing the lock which will block a competing thread from inserting another irq structure of the same irq number.
Suggested-by: Robin Murphy <robin.murphy@arm.com> Signed-off-by: Waiman Long <longman@redhat.com> --- drivers/perf/arm_dmc620_pmu.c | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-)
diff --git a/drivers/perf/arm_dmc620_pmu.c b/drivers/perf/arm_dmc620_pmu.c index 9d0f01c4455a..7cafd4dd4522 100644 --- a/drivers/perf/arm_dmc620_pmu.c +++ b/drivers/perf/arm_dmc620_pmu.c @@ -76,6 +76,7 @@ struct dmc620_pmu_irq { refcount_t refcount; unsigned int irq_num; unsigned int cpu; + unsigned int valid; }; struct dmc620_pmu { @@ -423,9 +424,14 @@ static struct dmc620_pmu_irq *__dmc620_pmu_get_irq(int irq_num) 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)) + list_for_each_entry(irq, &dmc620_pmu_irqs, irqs_node) { + if (irq->irq_num != irq_num) + continue; + if (!irq->valid) + return ERR_PTR(-EAGAIN); /* Try again later */ + if (refcount_inc_not_zero(&irq->refcount)) return irq; + } irq = kzalloc(sizeof(*irq), GFP_KERNEL); if (!irq) @@ -447,13 +453,23 @@ static struct dmc620_pmu_irq *__dmc620_pmu_get_irq(int irq_num) if (ret) goto out_free_irq; - ret = cpuhp_state_add_instance_nocalls(cpuhp_state_num, &irq->node); - if (ret) - goto out_free_irq; - irq->irq_num = irq_num; list_add(&irq->irqs_node, &dmc620_pmu_irqs); + /* + * Release dmc620_pmu_irqs_lock before calling + * cpuhp_state_add_instance_nocalls() and reacquire it afterward. + */ + mutex_unlock(&dmc620_pmu_irqs_lock); + ret = cpuhp_state_add_instance_nocalls(cpuhp_state_num, &irq->node); + mutex_lock(&dmc620_pmu_irqs_lock); + + if (ret) { + list_del(&irq->irqs_node); + goto out_free_irq; + } + + irq->valid = true; return irq; out_free_irq: -- 2.31.1
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