| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <a49858bf-fbe6-bec6-664a-7aad1ee53ffb@redhat.com>
Date: Fri, 11 Aug 2023 14:26:36 -0400
From: Waiman Long <longman@...hat.com>
To: Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>,
Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] perf/arm-dmc620: Fix
dmc620_pmu_irqs_lock/cpu_hotplug_lock circular lock dependency
On 8/10/23 13:21, Robin Murphy wrote:
> On 10/08/2023 4:41 pm, Waiman Long wrote:
>> 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() calls
>> cpuhp_state_add_instance_nocalls(). Since dmc620_pmu_irqs_lock is used
>> for protecting the dmc620_pmu_irqs structure, 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 adding a new dmc620_pmu_get_lock
>> for protecting the call to __dmc620_pmu_get_irq(). While at it, rename
>> dmc620_pmu_irqs_lock to dmc620_pmu_list_lock as it is now just
>> protecting
>> the iteration and modification of pmus_node and irqs_node lists.
>>
>> As a result, cpuhp_state_add_instance_nocalls() won't be called with
>> reanemd dmc620_pmu_list_lock held and cpu_hotplug_lock won't be acquired
>> after dmc620_pmu_list_lock.
>>
>> Suggested-by: Robin Murphy <robin.murphy@....com>
>> Signed-off-by: Waiman Long <longman@...hat.com>
>> ---
>> drivers/perf/arm_dmc620_pmu.c | 34 ++++++++++++++++++++++------------
>> 1 file changed, 22 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/perf/arm_dmc620_pmu.c
>> b/drivers/perf/arm_dmc620_pmu.c
>> index 9d0f01c4455a..a5bfc8f2e6ab 100644
>> --- a/drivers/perf/arm_dmc620_pmu.c
>> +++ b/drivers/perf/arm_dmc620_pmu.c
>> @@ -66,8 +66,14 @@
>> #define DMC620_PMU_COUNTERn_OFFSET(n) \
>> (DMC620_PMU_COUNTERS_BASE + 0x28 * (n))
>> +/*
>> + * The allowable lock ordering is:
>> + * - dmc620_pmu_get_lock (protects call to __dmc620_pmu_get_irq())
>> + * - dmc620_pmu_list_lock (protects pmus_node & irqs_node lists)
>
> Sorry, this isn't right: touching the irqs_node list *is* the aspect
> of __dmc620_pmu_get_irq() which warrants globally locking. It's then
> the pmus_node lists which want locking separately from that - those
> could strictly be locked per dmc620_pmu_irq instance, but that would
> be a big waste of space, so we can still combine them under a single
> global lock. I just went too far in thinking I could get away with
> (ab)using the same lock for both purposes since they didn't overlap :)
OK, you want separate locks for pmus_node list and irqs_node list. That
will be fine too. I can make the change.
Thanks,
Longman
>
>> + */
>> +static DEFINE_MUTEX(dmc620_pmu_get_lock);
>> +static DEFINE_MUTEX(dmc620_pmu_list_lock);
>> static LIST_HEAD(dmc620_pmu_irqs);
>> -static DEFINE_MUTEX(dmc620_pmu_irqs_lock);
>> struct dmc620_pmu_irq {
>> struct hlist_node node;
>> @@ -423,9 +429,11 @@ static struct dmc620_pmu_irq
>> *__dmc620_pmu_get_irq(int irq_num)
>> struct dmc620_pmu_irq *irq;
>> int ret;
>> + mutex_lock(&dmc620_pmu_list_lock);
>> 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 unlock_out;
>> + mutex_unlock(&dmc620_pmu_list_lock);
>> irq = kzalloc(sizeof(*irq), GFP_KERNEL);
>> if (!irq)
>> @@ -452,8 +460,10 @@ 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_list_lock);
>> list_add(&irq->irqs_node, &dmc620_pmu_irqs);
>> -
>> +unlock_out:
>> + mutex_unlock(&dmc620_pmu_list_lock);
>> return irq;
>> out_free_irq:
>> @@ -467,17 +477,17 @@ static int dmc620_pmu_get_irq(struct dmc620_pmu
>> *dmc620_pmu, int irq_num)
>> {
>> struct dmc620_pmu_irq *irq;
>> - mutex_lock(&dmc620_pmu_irqs_lock);
>> + mutex_lock(&dmc620_pmu_get_lock);
>> irq = __dmc620_pmu_get_irq(irq_num);
>> - mutex_unlock(&dmc620_pmu_irqs_lock);
>> + mutex_unlock(&dmc620_pmu_get_lock);
>> if (IS_ERR(irq))
>> return PTR_ERR(irq);
>> dmc620_pmu->irq = irq;
>> - mutex_lock(&dmc620_pmu_irqs_lock);
>> + mutex_lock(&dmc620_pmu_list_lock);
>> list_add_rcu(&dmc620_pmu->pmus_node, &irq->pmus_node);
>> - mutex_unlock(&dmc620_pmu_irqs_lock);
>> + mutex_unlock(&dmc620_pmu_list_lock);
>> return 0;
>> }
>> @@ -486,16 +496,16 @@ static void dmc620_pmu_put_irq(struct
>> dmc620_pmu *dmc620_pmu)
>> {
>> struct dmc620_pmu_irq *irq = dmc620_pmu->irq;
>> - mutex_lock(&dmc620_pmu_irqs_lock);
>> + mutex_lock(&dmc620_pmu_list_lock);
>> list_del_rcu(&dmc620_pmu->pmus_node);
>
> Ah, it might be the laziness in this function that's misled you.
> Logically it ought to just be a case of dropping pmu_list_lock here
> after removing from the pmus_node list, then taking pmu_get_lock
> before the following list_del from the main global list (I think that
> shouldn't *need* to cover the refcount operation as well, but equally
> there's probably no harm if it does).
>
> Thanks,
> Robin.
>
>> if (!refcount_dec_and_test(&irq->refcount)) {
>> - mutex_unlock(&dmc620_pmu_irqs_lock);
>> + mutex_unlock(&dmc620_pmu_list_lock);
>> return;
>> }
>> list_del(&irq->irqs_node);
>> - mutex_unlock(&dmc620_pmu_irqs_lock);
>> + mutex_unlock(&dmc620_pmu_list_lock);
>> free_irq(irq->irq_num, irq);
>> cpuhp_state_remove_instance_nocalls(cpuhp_state_num, &irq->node);
>> @@ -638,10 +648,10 @@ static int dmc620_pmu_cpu_teardown(unsigned int
>> cpu,
>> return 0;
>> /* We're only reading, but this isn't the place to be
>> involving RCU */
>> - mutex_lock(&dmc620_pmu_irqs_lock);
>> + mutex_lock(&dmc620_pmu_list_lock);
>> list_for_each_entry(dmc620_pmu, &irq->pmus_node, pmus_node)
>> perf_pmu_migrate_context(&dmc620_pmu->pmu, irq->cpu, target);
>> - mutex_unlock(&dmc620_pmu_irqs_lock);
>> + mutex_unlock(&dmc620_pmu_list_lock);
>> WARN_ON(irq_set_affinity(irq->irq_num, cpumask_of(target)));
>> irq->cpu = target;
>
Powered by blists - more mailing lists