irq: Track the owner of irq descriptor

Interrupt descriptors can be allocated from modules. The interrupts
are used by other modules, but we have no refcount on the module which
provides the interrupts and there is no way to establish one on the
device level as the interrupt using module is agnostic to the fact
that the interrupt is provided by a module rather than by some builtin
interrupt controller.

To prevent removal of the interrupt providing module, we can track the
owner of the interrupt descriptor, which also provides the relevant
irq chip functions in the irq descriptor.

request/setup_irq() can now acquire a refcount on the owner module to
prevent unloading. free_irq() drops the refcount.
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Link: http://lkml.kernel.org/r/20110711101731.GA13804@Chamillionaire.breakpoint.ccSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/irq.h

@@ -23,6 +23,7 @@
 #include <linux/errno.h>
 #include <linux/topology.h>
 #include <linux/wait.h>
+#include <linux/module.h>
 
 #include <asm/irq.h>
 #include <asm/ptrace.h>
@@ -546,7 +547,15 @@ static inline struct msi_desc *irq_data_get_msi(struct irq_data *d)
 	return d->msi_desc;
 }
 
-int irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node);
+int __irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node,
+		struct module *owner);
+
+static inline int irq_alloc_descs(int irq, unsigned int from, unsigned int cnt,
+		int node)
+{
+	return __irq_alloc_descs(irq, from, cnt, node, THIS_MODULE);
+}
+
 void irq_free_descs(unsigned int irq, unsigned int cnt);
 int irq_reserve_irqs(unsigned int from, unsigned int cnt);
 

include/linux/irqdesc.h

@@ -66,6 +66,7 @@ struct irq_desc {
 #ifdef CONFIG_PROC_FS
 	struct proc_dir_entry	*dir;
 #endif
+	struct module		*owner;
 	const char		*name;
 } ____cacheline_internodealigned_in_smp;
 

kernel/irq/irqdesc.c

@@ -70,7 +70,8 @@ static inline void desc_smp_init(struct irq_desc *desc, int node) { }
 static inline int desc_node(struct irq_desc *desc) { return 0; }
 #endif
 
-static void desc_set_defaults(unsigned int irq, struct irq_desc *desc, int node)
+static void desc_set_defaults(unsigned int irq, struct irq_desc *desc, int node,
+		struct module *owner)
 {
 	int cpu;
 
@@ -86,6 +87,7 @@ static void desc_set_defaults(unsigned int irq, struct irq_desc *desc, int node)
 	desc->irq_count = 0;
 	desc->irqs_unhandled = 0;
 	desc->name = NULL;
+	desc->owner = owner;
 	for_each_possible_cpu(cpu)
 		*per_cpu_ptr(desc->kstat_irqs, cpu) = 0;
 	desc_smp_init(desc, node);
@@ -128,7 +130,7 @@ static void free_masks(struct irq_desc *desc)
 static inline void free_masks(struct irq_desc *desc) { }
 #endif
 
-static struct irq_desc *alloc_desc(int irq, int node)
+static struct irq_desc *alloc_desc(int irq, int node, struct module *owner)
 {
 	struct irq_desc *desc;
 	gfp_t gfp = GFP_KERNEL;
@@ -147,7 +149,7 @@ static struct irq_desc *alloc_desc(int irq, int node)
 	raw_spin_lock_init(&desc->lock);
 	lockdep_set_class(&desc->lock, &irq_desc_lock_class);
 
-	desc_set_defaults(irq, desc, node);
+	desc_set_defaults(irq, desc, node, owner);
 
 	return desc;
 
@@ -173,13 +175,14 @@ static void free_desc(unsigned int irq)
 	kfree(desc);
 }
 
-static int alloc_descs(unsigned int start, unsigned int cnt, int node)
+static int alloc_descs(unsigned int start, unsigned int cnt, int node,
+		       struct module *owner)
 {
 	struct irq_desc *desc;
 	int i;
 
 	for (i = 0; i < cnt; i++) {
-		desc = alloc_desc(start + i, node);
+		desc = alloc_desc(start + i, node, owner);
 		if (!desc)
 			goto err;
 		mutex_lock(&sparse_irq_lock);
@@ -227,7 +230,7 @@ int __init early_irq_init(void)
 		nr_irqs = initcnt;
 
 	for (i = 0; i < initcnt; i++) {
-		desc = alloc_desc(i, node);
+		desc = alloc_desc(i, node, NULL);
 		set_bit(i, allocated_irqs);
 		irq_insert_desc(i, desc);
 	}
@@ -261,7 +264,7 @@ int __init early_irq_init(void)
 		alloc_masks(&desc[i], GFP_KERNEL, node);
 		raw_spin_lock_init(&desc[i].lock);
 		lockdep_set_class(&desc[i].lock, &irq_desc_lock_class);
-		desc_set_defaults(i, &desc[i], node);
+		desc_set_defaults(i, &desc[i], node, NULL);
 	}
 	return arch_early_irq_init();
 }
@@ -276,8 +279,16 @@ static void free_desc(unsigned int irq)
 	dynamic_irq_cleanup(irq);
 }
 
-static inline int alloc_descs(unsigned int start, unsigned int cnt, int node)
+static inline int alloc_descs(unsigned int start, unsigned int cnt, int node,
+			      struct module *owner)
 {
+	u32 i;
+
+	for (i = 0; i < cnt; i++) {
+		struct irq_desc *desc = irq_to_desc(start + i);
+
+		desc->owner = owner;
+	}
 	return start;
 }
 
@@ -337,7 +348,8 @@ EXPORT_SYMBOL_GPL(irq_free_descs);
  * Returns the first irq number or error code
  */
 int __ref
-irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node)
+__irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node,
+		  struct module *owner)
 {
 	int start, ret;
 
@@ -366,13 +378,13 @@ irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node)
 
 	bitmap_set(allocated_irqs, start, cnt);
 	mutex_unlock(&sparse_irq_lock);
-	return alloc_descs(start, cnt, node);
+	return alloc_descs(start, cnt, node, owner);
 
 err:
 	mutex_unlock(&sparse_irq_lock);
 	return ret;
 }
-EXPORT_SYMBOL_GPL(irq_alloc_descs);
+EXPORT_SYMBOL_GPL(__irq_alloc_descs);
 
 /**
  * irq_reserve_irqs - mark irqs allocated
@@ -440,7 +452,7 @@ void dynamic_irq_cleanup(unsigned int irq)
 	unsigned long flags;
 
 	raw_spin_lock_irqsave(&desc->lock, flags);
-	desc_set_defaults(irq, desc, desc_node(desc));
+	desc_set_defaults(irq, desc, desc_node(desc), NULL);
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
 }
 

kernel/irq/manage.c

@@ -883,6 +883,8 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 
 	if (desc->irq_data.chip == &no_irq_chip)
 		return -ENOSYS;
+	if (!try_module_get(desc->owner))
+		return -ENODEV;
 	/*
 	 * Some drivers like serial.c use request_irq() heavily,
 	 * so we have to be careful not to interfere with a
@@ -906,8 +908,10 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 	 */
 	nested = irq_settings_is_nested_thread(desc);
 	if (nested) {
-		if (!new->thread_fn)
-			return -EINVAL;
+		if (!new->thread_fn) {
+			ret = -EINVAL;
+			goto out_mput;
+		}
 		/*
 		 * Replace the primary handler which was provided from
 		 * the driver for non nested interrupt handling by the
@@ -929,8 +933,10 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 
 		t = kthread_create(irq_thread, new, "irq/%d-%s", irq,
 				   new->name);
-		if (IS_ERR(t))
-			return PTR_ERR(t);
+		if (IS_ERR(t)) {
+			ret = PTR_ERR(t);
+			goto out_mput;
+		}
 		/*
 		 * We keep the reference to the task struct even if
 		 * the thread dies to avoid that the interrupt code
@@ -1095,6 +1101,8 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 			kthread_stop(t);
 		put_task_struct(t);
 	}
+out_mput:
+	module_put(desc->owner);
 	return ret;
 }
 
@@ -1203,6 +1211,7 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
 		put_task_struct(action->thread);
 	}
 
+	module_put(desc->owner);
 	return action;
 }