path: root/kernel/irq
diff options
authorThomas Gleixner <>2015-12-13 18:02:22 +0100
committerThomas Gleixner <>2015-12-14 10:03:46 +0100
commit425a5072dcd1bd895eea90a6b495392b6358ebd0 (patch)
tree312ffe3eee07e6fd1ae14732b2d67273df053548 /kernel/irq
parentf0cb32207307e9d7b3ee8117078b7a37f8d0166e (diff)
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 <> Cc: Keith Busch <>
Diffstat (limited to 'kernel/irq')
1 files changed, 16 insertions, 3 deletions
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 239e2ae2c947..0409da0bcc33 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -159,6 +159,7 @@ static struct irq_desc *alloc_desc(int irq, int node, struct module *owner)
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)
- 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,