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genirq: Free irq_desc with rcu

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The new VMD device driver needs to iterate over a list of
"demultiplexing" interrupts. Protecting that list with a lock is not
possible because the list is also required in code pathes which hold
irq descriptor lock. Therefor the demultiplexing interrupt handler
would create a lock inversion scenario if it calls a demux handler
with the list protection lock held.

A solution for this is to free the irq descriptor via RCU, so the
list can be walked with rcu read lock held.

Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Keith Busch <[email protected]>
This commit is contained in:
Thomas Gleixner 2015-12-13 18:02:22 +01:00
commit 425a5072dc
2 changed files with 22 additions and 3 deletions
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19
kernel/irq/irqdesc.c
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@ -159,6 +159,7 @@ static struct irq_desc *alloc_desc(int irq, int node, struct module *owner)
raw_spin_lock_init(&desc->lock);
lockdep_set_class(&desc->lock, &irq_desc_lock_class);
init_rcu_head(&desc->rcu);
desc_set_defaults(irq, desc, node, owner);
@ -171,6 +172,15 @@ err_desc:
return NULL;
}
static void delayed_free_desc(struct rcu_head *rhp)
{
struct irq_desc *desc = container_of(rhp, struct irq_desc, rcu);
free_masks(desc);
free_percpu(desc->kstat_irqs);
kfree(desc);
}
static void free_desc(unsigned int irq)
{
struct irq_desc *desc = irq_to_desc(irq);
@ -187,9 +197,12 @@ static void free_desc(unsigned int irq)
delete_irq_desc(irq);
mutex_unlock(&sparse_irq_lock);
free_masks(desc);
free_percpu(desc->kstat_irqs);
kfree(desc);
/*
* We free the descriptor, masks and stat fields via RCU. That
* allows demultiplex interrupts to do rcu based management of
* the child interrupts.
*/
call_rcu(&desc->rcu, delayed_free_desc);
}
static int alloc_descs(unsigned int start, unsigned int cnt, int node,