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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 <tglx@linutronix.de>
Cc: Keith Busch <keith.busch@intel.com>
This commit is contained in:
Thomas Gleixner 2015-12-13 18:02:22 +01:00
parent f0cb322073
commit 425a5072dc
2 changed files with 22 additions and 3 deletions
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6
include/linux/irqdesc.h
View file

@ -1,6 +1,8 @@
#ifndef _LINUX_IRQDESC_H #ifndef _LINUX_IRQDESC_H
#define _LINUX_IRQDESC_H #define _LINUX_IRQDESC_H
#include <linux/rcupdate.h>
/* /*
* Core internal functions to deal with irq descriptors * Core internal functions to deal with irq descriptors
*/ */
@ -40,6 +42,7 @@ struct pt_regs;
* IRQF_NO_SUSPEND set * IRQF_NO_SUSPEND set
* @force_resume_depth: number of irqactions on a irq descriptor with * @force_resume_depth: number of irqactions on a irq descriptor with
* IRQF_FORCE_RESUME set * IRQF_FORCE_RESUME set
* @rcu: rcu head for delayed free
* @dir: /proc/irq/ procfs entry * @dir: /proc/irq/ procfs entry
* @name: flow handler name for /proc/interrupts output * @name: flow handler name for /proc/interrupts output
*/ */
@ -81,6 +84,9 @@ struct irq_desc {
#endif #endif
#ifdef CONFIG_PROC_FS #ifdef CONFIG_PROC_FS
struct proc_dir_entry *dir; struct proc_dir_entry *dir;
#endif
#ifdef CONFIG_SPARSE_IRQ
struct rcu_head rcu;
#endif #endif
int parent_irq; int parent_irq;
struct module *owner; struct module *owner;

19
kernel/irq/irqdesc.c
View file

@ -159,6 +159,7 @@ static struct irq_desc *alloc_desc(int irq, int node, struct module *owner)
raw_spin_lock_init(&desc->lock); raw_spin_lock_init(&desc->lock);
lockdep_set_class(&desc->lock, &irq_desc_lock_class); lockdep_set_class(&desc->lock, &irq_desc_lock_class);
init_rcu_head(&desc->rcu);
desc_set_defaults(irq, desc, node, owner); desc_set_defaults(irq, desc, node, owner);
@ -171,6 +172,15 @@ err_desc:
return NULL; 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) static void free_desc(unsigned int irq)
{ {
struct irq_desc *desc = irq_to_desc(irq); struct irq_desc *desc = irq_to_desc(irq);
@ -187,9 +197,12 @@ static void free_desc(unsigned int irq)
delete_irq_desc(irq); delete_irq_desc(irq);
mutex_unlock(&sparse_irq_lock); mutex_unlock(&sparse_irq_lock);
free_masks(desc); /*
free_percpu(desc->kstat_irqs); * We free the descriptor, masks and stat fields via RCU. That
kfree(desc); * 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, static int alloc_descs(unsigned int start, unsigned int cnt, int node,