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SubjectRe: [PATCH] x86/apic/vector: Move pr_warn() outside of vector_lock
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On 3/28/21 6:04 PM, Thomas Gleixner wrote:
> Waiman,
>
> On Sun, Mar 28 2021 at 15:58, Waiman Long wrote:
>> It was found that the following circular locking dependency warning
>> could happen in some systems:
>>
>> [ 218.097878] ======================================================
>> [ 218.097879] WARNING: possible circular locking dependency detected
>> [ 218.097880] 4.18.0-228.el8.x86_64+debug #1 Not tainted
>> [ 218.097881] ------------------------------------------------------
>> [ 218.097882] systemd/1 is trying to acquire lock:
>> [ 218.097883] ffffffff84c27920 (console_owner){-.-.}, at: console_unlock+0x3fb/0x9f0
>> [ 218.097886]
>> [ 218.097887] but task is already holding lock:
>> [ 218.097888] ffffffff84afca78 (vector_lock){-.-.}, at: x86_vector_activate+0xca/0xab0
>> [ 218.097891]
>> [ 218.097892] which lock already depends on the new lock.
>> :
>> [ 218.097966] other info that might help us debug this:
>> [ 218.097967]
>> [ 218.097967] Chain exists of:
>> [ 218.097968] console_oc_lock_class --> vector_lock
>> [ 218.097972]
>> [ 218.097973] Possible unsafe locking scenario:
>> [ 218.097973]
>> [ 218.097974] CPU0 CPU1
>> [ 218.097975] ---- ----
>> [ 218.097975] lock(vector_lock);
>> [ 218.097977] lock(&irq_desc_lock_class);
>> [ 218.097980] lock(vector_lock);
>> [ 218.097981] lock(console_owner);
>> [ 218.097983]
>> [ 218.097984] *** DEADLOCK ***
> can you please post the full lockdep output?

Will do.


>> This lockdep warning was causing by printing of the warning message:
>>
>> [ 218.095152] irq 3: Affinity broken due to vector space exhaustion.
>>
>> It looks that this warning message is relatively more common than
>> the other warnings in arch/x86/kernel/apic/vector.c. To avoid this
>> potential deadlock scenario, this patch moves all the pr_warn() calls
>> in the vector.c file outside of the vector_lock critical sections.
> Definitely not.
>
>> -static int activate_reserved(struct irq_data *irqd)
>> +static int activate_reserved(struct irq_data *irqd, unsigned long flags,
>> + bool *unlocked)
>> {
>> struct apic_chip_data *apicd = apic_chip_data(irqd);
>> int ret;
>> @@ -410,6 +411,8 @@ static int activate_reserved(struct irq_data *irqd)
>> */
>> if (!cpumask_subset(irq_data_get_effective_affinity_mask(irqd),
>> irq_data_get_affinity_mask(irqd))) {
>> + raw_spin_unlock_irqrestore(&vector_lock, flags);
>> + *unlocked = true;
> What?
>
>> pr_warn("irq %u: Affinity broken due to vector space exhaustion.\n",
>> irqd->irq);
>> }
>> @@ -446,6 +449,7 @@ static int x86_vector_activate(struct irq_domain *dom, struct irq_data *irqd,
>> {
>> struct apic_chip_data *apicd = apic_chip_data(irqd);
>> unsigned long flags;
>> + bool unlocked = false;
>> int ret = 0;
>>
>> trace_vector_activate(irqd->irq, apicd->is_managed,
>> @@ -459,8 +463,9 @@ static int x86_vector_activate(struct irq_domain *dom, struct irq_data *irqd,
>> else if (apicd->is_managed)
>> ret = activate_managed(irqd);
>> else if (apicd->has_reserved)
>> - ret = activate_reserved(irqd);
>> - raw_spin_unlock_irqrestore(&vector_lock, flags);
>> + ret = activate_reserved(irqd, flags, &unlocked);
>> + if (!unlocked)
>> + raw_spin_unlock_irqrestore(&vector_lock, flags);
> Even moar what?
>
>> return ret;
>> }
> This turns that code into complete unreadable gunk. No way.

I am sorry that this part of the patch is sloppy. I will revise it to
make it better.

Cheers,
Longman


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