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Message-ID: <84b23b62-0813-34eb-5afc-da21597d218f@caviumnetworks.com>
Date: Tue, 15 Aug 2017 11:00:19 -0700
From: David Daney <ddaney@...iumnetworks.com>
To: Marc Zyngier <marc.zyngier@....com>,
David Daney <david.daney@...ium.com>,
Linus Walleij <linus.walleij@...aro.org>,
Alexandre Courbot <gnurou@...il.com>,
Mark Rutland <mark.rutland@....com>,
Thomas Gleixner <tglx@...utronix.de>,
linux-gpio@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 3/5] irqdomain: Add irq_domain_{push,pop}_irq()
functions.
On 08/15/2017 06:50 AM, Marc Zyngier wrote:
> Hi David,
>
> On 09/08/17 23:51, David Daney wrote:
[...]
>> diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
>> index f1f2514..629f770 100644
>> --- a/kernel/irq/irqdomain.c
>> +++ b/kernel/irq/irqdomain.c
>> @@ -1448,6 +1448,184 @@ int __irq_domain_alloc_irqs(struct irq_domain *domain, int irq_base,
>> return ret;
>> }
>>
>> +/* The irq_data was moved, fix the revmap to refer to the new location */
>> +static void irq_domain_fix_revmap(struct irq_data *d)
>> +{
>> + void **slot;
>> +
>> + if (d->hwirq < d->domain->revmap_size)
>> + return; /* Not using radix tree. */
>> +
>> + /* Fix up the revmap. */
>> + mutex_lock(&revmap_trees_mutex);
>> + slot = radix_tree_lookup_slot(&d->domain->revmap_tree, d->hwirq);
>> + if (slot)
>> + radix_tree_replace_slot(&d->domain->revmap_tree, slot, d);
>
> radix_tree_replace_slot already deals with non-existing entries, so the
> initial radix_tree_lookup_slot call is superfluous.
This comment I don't understand. To replace an element in the tree, you
must know the slot. I see no alternative to calling
radix_tree_lookup_slot(). If I am mistaken, it would be helpful to know
in a little more detail how you think it should be done.
>
>> + mutex_unlock(&revmap_trees_mutex);
>> +}
>> +
>> +/**
>> + * irq_domain_push_irq() - Push a domain in to the top of a hierarchy.
>> + * @domain: Domain to push.
>> + * @virq: Irq to push the domain in to.
>> + * @arg: Passed to the irq_domain_ops alloc() function.
>> + *
>> + * For an already existing irqdomain hierarchy, as might be obtained
>> + * via a call to pci_enable_msix(), add an additional domain to the
>> + * head of the processing chain. Must be called before request_irq()
>> + * has been called.
>> + */
>> +int irq_domain_push_irq(struct irq_domain *domain, int virq, void *arg)
>> +{
>> + struct irq_data *child_irq_data;
>> + struct irq_data *root_irq_data = irq_get_irq_data(virq);
>> + struct irq_desc *desc;
>> + int rv = 0;
>> +
>> + /*
>> + * Check that no action has been set, which indicates the virq
>> + * is in a state where this function doesn't have to deal with
>> + * races between interrupt handling and maintaining the
>> + * hierarchy. This will catch gross misuse. Attempting to
>> + * make the check race free would require holding locks across
>> + * calls to struct irq_domain_ops->alloc(), which could lead
>> + * to deadlock, so we just do a simple check before starting.
>> + */
>> + desc = irq_to_desc(virq);
>> + if (!desc)
>> + return -EINVAL;
>> + if (WARN_ON(desc->action))
>> + return -EBUSY;
>> +
>> + if (domain == NULL)
>> + return -EINVAL;
>> +
>> + if (WARN_ON(!domain->ops->alloc))
>> + return -EINVAL;
>
> I'd rather you use irq_domain_is_hierarchy() instead. Same effect, but
> less likely to break in the long run.
Good idea, I will do it.
>
>> +
>> + if (!root_irq_data)
>> + return -EINVAL;
>> +
>> + child_irq_data = kzalloc_node(sizeof(*child_irq_data), GFP_KERNEL,
>> + irq_data_get_node(root_irq_data));
>> + if (!child_irq_data)
>> + return -ENOMEM;
>> +
>> + mutex_lock(&irq_domain_mutex);
>> +
>> + /* Copy the original irq_data. */
>> + *child_irq_data = *root_irq_data;
>> +
>> + irq_domain_fix_revmap(child_irq_data);
>
> What is the benefit of updating the revmap early?
The idea was to have it be valid for the ops->alloc() call, but ...
> We don't do that in
> the pop case. Can't we do it in one go once the allocation has succeeded?
... the code in irqdomain.c that calls ops->alloc() doesn't have revmap
established at the call site, so I agree that this can go after the
allocation so we don't have to undo it on failure.
>
>> +
>> + /*
>> + * Overwrite the root_irq_data, which is embedded in struct
>> + * irq_desc, with values for this domain.
>> + */
>> + root_irq_data->parent_data = child_irq_data;
>> + root_irq_data->domain = domain;
>> + root_irq_data->mask = 0;
>> + root_irq_data->hwirq = 0;
>> + root_irq_data->chip = NULL;
>> + root_irq_data->chip_data = NULL;
>> + rv = domain->ops->alloc(domain, virq, 1, arg);
>
> That'd be irq_domain_alloc_irqs_hierarchy().
>
Yes.
> Overall, I'm a bit concerned that alloc() is allowed to be recursive
> itself. Hopefully nobody will do that, but you never know. A possible
> way of trapping this would be to only set parent_data *after* the
> allocation has been done.
I will try it.
>
> Another concern is that I never see domain->parent being checked. It
> should match child_irq_data->domain, so that you can never push a domain
> on an interrupt that is not part of the parent domain.
I will add a check for this.
>
>> + if (rv) {
>> + /* Restore the original irq_data. */
>> + *root_irq_data = *child_irq_data;
>> + irq_domain_fix_revmap(root_irq_data);
>> + goto error;
>> + }
>> +
>> + if (root_irq_data->hwirq < domain->revmap_size) {
>> + domain->linear_revmap[root_irq_data->hwirq] = virq;
>> + } else {
>> + mutex_lock(&revmap_trees_mutex);
>> + radix_tree_insert(&domain->revmap_tree,
>> + root_irq_data->hwirq, root_irq_data);
>> + mutex_unlock(&revmap_trees_mutex);
>> + }
>
> We already have this exact code twice (in irq_domain_insert_irq and
> irq_domain_associate). How about making it a helper?
OK.
>
>> +error:
>> + mutex_unlock(&irq_domain_mutex);
>> +
>> + return rv;
>> +}
>> +EXPORT_SYMBOL_GPL(irq_domain_push_irq);
>> +
>> +/**
>> + * irq_domain_pop_irq() - Remove a domain from the top of a hierarchy.
>> + * @domain: Domain to remove.
>> + * @virq: Irq to remove the domain from.
>> + *
>> + * Undo the effects of a call to irq_domain_push_irq(). Must be
>> + * called either before request_irq() or after free_irq().
>> + */
>> +int irq_domain_pop_irq(struct irq_domain *domain, int virq)
>> +{
>> + struct irq_data *root_irq_data = irq_get_irq_data(virq);
>> + struct irq_data *child_irq_data;
>> + struct irq_data *tmp_irq_data;
>> + struct irq_desc *desc;
>> +
>> + /*
>> + * Check that no action is set, which indicates the virq is in
>> + * a state where this function doesn't have to deal with races
>> + * between interrupt handling and maintaining the hierarchy.
>> + * This will catch gross misuse. Attempting to make the check
>> + * race free would require holding locks across calls to
>> + * struct irq_domain_ops->free(), which could lead to
>> + * deadlock, so we just do a simple check before starting.
>> + */
>> + desc = irq_to_desc(virq);
>> + if (!desc)
>> + return -EINVAL;
>> + if (WARN_ON(desc->action))
>> + return -EBUSY;
>> +
>> + if (domain == NULL)
>> + return -EINVAL;
>> +
>> + if (!root_irq_data)
>> + return -EINVAL;
>> +
>> + tmp_irq_data = irq_domain_get_irq_data(domain, virq);
>> +
>> + /* We can only "pop" if this domain is at the top of the list */
>> + if (WARN_ON(root_irq_data != tmp_irq_data))
>> + return -EINVAL;
>> +
>> + if (WARN_ON(root_irq_data->domain != domain))
>> + return -EINVAL;
>> +
>> + child_irq_data = root_irq_data->parent_data;
>> + if (WARN_ON(!child_irq_data))
>> + return -EINVAL;
>> +
>> + mutex_lock(&irq_domain_mutex);
>> +
>> + root_irq_data->parent_data = NULL;
>> +
>> + if (root_irq_data->hwirq >= domain->revmap_size) {
>> + mutex_lock(&revmap_trees_mutex);
>> + radix_tree_delete(&domain->revmap_tree, root_irq_data->hwirq);
>> + mutex_unlock(&revmap_trees_mutex);ops->alloc()
>> + }
>
> What about clearing it from the revmap if it fits there? Also, this code
> already exists in irq_domain_disassociate and irq_domain_remove_irq, and
> making that a helper is overdue.
I will investigate doing something like that.
>
>> +
>> + if (domain->ops->free)
>> + domain->ops->free(domain, virq, 1);
>
> Use irq_domain_free_irqs_hierarchy(), making it conditional in that helper.
OK
>
>> +
>> + /* Restore the original irq_data. */
>> + *root_irq_data = *child_irq_data;
>> +
>> + irq_domain_fix_revmap(root_irq_data);
>> +
>> + mutex_unlock(&irq_domain_mutex);
>> +
>> + kfree(child_irq_data);
>> +
>> + return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(irq_domain_pop_irq);
>> +
>> /**
>> * irq_domain_free_irqs - Free IRQ number and associated data structures
>> * @virq: base IRQ number
>>
>
> Thanks,
>
> M.
>
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