Commit 425a5072 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Keith Busch <keith.busch@intel.com>
parent f0cb3220

include/linux/irqdesc.h

+6 −0
Original line number Diff line number Diff line 
#ifndef _LINUX_IRQDESC_H

#define _LINUX_IRQDESC_H



#include <linux/rcupdate.h>



/*

 * Core internal functions to deal with irq descriptors

 */
@@ -40,6 +42,7 @@ struct pt_regs; 
 *			IRQF_NO_SUSPEND set

 * @force_resume_depth:	number of irqactions on a irq descriptor with

 *			IRQF_FORCE_RESUME set

 * @rcu:		rcu head for delayed free

 * @dir:		/proc/irq/ procfs entry

 * @name:		flow handler name for /proc/interrupts output

 */
@@ -81,6 +84,9 @@ struct irq_desc { 
#endif

#ifdef CONFIG_PROC_FS

	struct proc_dir_entry	*dir;

#endif

#ifdef CONFIG_SPARSE_IRQ

	struct rcu_head		rcu;

#endif

	int			parent_irq;

	struct module		*owner;

kernel/irq/irqdesc.c

+16 −3
Original line number Diff line number Diff line
@@ -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,

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