genirq: Free irq_desc with rcu
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 <tglx@linutronix.de>
Cc: Keith Busch <keith.busch@intel.com>
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 239e2ae..0409da0 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -159,6 +159,7 @@
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 @@
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 @@
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,