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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>
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@ -1,6 +1,8 @@
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#ifndef _LINUX_IRQDESC_H
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#define _LINUX_IRQDESC_H
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#include <linux/rcupdate.h>
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/*
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* Core internal functions to deal with irq descriptors
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*/
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@ -40,6 +42,7 @@ struct pt_regs;
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* IRQF_NO_SUSPEND set
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* @force_resume_depth: number of irqactions on a irq descriptor with
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* IRQF_FORCE_RESUME set
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* @rcu: rcu head for delayed free
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* @dir: /proc/irq/ procfs entry
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* @name: flow handler name for /proc/interrupts output
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*/
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@ -81,6 +84,9 @@ struct irq_desc {
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#endif
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#ifdef CONFIG_PROC_FS
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struct proc_dir_entry *dir;
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#endif
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#ifdef CONFIG_SPARSE_IRQ
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struct rcu_head rcu;
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#endif
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int parent_irq;
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struct module *owner;
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@ -159,6 +159,7 @@ static struct irq_desc *alloc_desc(int irq, int node, struct module *owner)
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raw_spin_lock_init(&desc->lock);
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lockdep_set_class(&desc->lock, &irq_desc_lock_class);
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init_rcu_head(&desc->rcu);
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desc_set_defaults(irq, desc, node, owner);
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@ -171,6 +172,15 @@ err_desc:
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return NULL;
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}
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static void delayed_free_desc(struct rcu_head *rhp)
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{
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struct irq_desc *desc = container_of(rhp, struct irq_desc, rcu);
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free_masks(desc);
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free_percpu(desc->kstat_irqs);
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kfree(desc);
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}
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static void free_desc(unsigned int irq)
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{
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struct irq_desc *desc = irq_to_desc(irq);
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@ -187,9 +197,12 @@ static void free_desc(unsigned int irq)
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delete_irq_desc(irq);
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mutex_unlock(&sparse_irq_lock);
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free_masks(desc);
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free_percpu(desc->kstat_irqs);
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kfree(desc);
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/*
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* We free the descriptor, masks and stat fields via RCU. That
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* allows demultiplex interrupts to do rcu based management of
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* the child interrupts.
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*/
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call_rcu(&desc->rcu, delayed_free_desc);
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}
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static int alloc_descs(unsigned int start, unsigned int cnt, int node,
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