Re: [PATCH] x86/apic/vector: Move pr_warn() outside of vector_lock

[Waiman Long]

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