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Commit 89c9b66b authored by Jan Glauber's avatar Jan Glauber Committed by Martin Schwidefsky
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[S390] race safe external interrupt registration 



The (un-)register_external_interrupt functions are not race safe if
more than one interrupt handler is added or deleted for an external
interrupt concurrently.

Make the registration / unregistration of external interrupts race safe
by using RCU and a spinlock. RCU is used to avoid a performance penalty
in the external interrupt handler, the register and unregister functions
are protected by the spinlock and are not performance critical.
call_rcu must be used since the SCLP driver uses the interface with
IRQs disabled. Also use the generic list implementation rather than
homebrewn list code.

Signed-off-by: default avatarJan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 9e280f66

arch/s390/kernel/irq.c

+46 −37
Original line number Diff line number Diff line
@@ -87,15 +87,6 @@ int show_interrupts(struct seq_file *p, void *v) 
        return 0;

}



/*

 * For compatibilty only. S/390 specific setup of interrupts et al. is done

 * much later in init_channel_subsystem().

 */

void __init init_IRQ(void)

{

	/* nothing... */

}



/*

 * Switch to the asynchronous interrupt stack for softirq execution.

 */
@@ -144,28 +135,45 @@ void init_irq_proc(void) 
#endif



/*

 * ext_int_hash[index] is the start of the list for all external interrupts

 * that hash to this index. With the current set of external interrupts

 * (0x1202 external call, 0x1004 cpu timer, 0x2401 hwc console, 0x4000

 * iucv and 0x2603 pfault) this is always the first element.

 * ext_int_hash[index] is the list head for all external interrupts that hash

 * to this index.

 */

static struct list_head ext_int_hash[256];



struct ext_int_info {

	struct ext_int_info *next;

	ext_int_handler_t handler;

	u16 code;

	struct list_head entry;

	struct rcu_head rcu;

};



static struct ext_int_info *ext_int_hash[256];

/* ext_int_hash_lock protects the handler lists for external interrupts */

DEFINE_SPINLOCK(ext_int_hash_lock);



static void __init init_external_interrupts(void)

{

	int idx;



	for (idx = 0; idx < ARRAY_SIZE(ext_int_hash); idx++)

		INIT_LIST_HEAD(&ext_int_hash[idx]);

}



static inline int ext_hash(u16 code)

{

	return (code + (code >> 9)) & 0xff;

}



static void ext_int_hash_update(struct rcu_head *head)

{

	struct ext_int_info *p = container_of(head, struct ext_int_info, rcu);



	kfree(p);

}



int register_external_interrupt(u16 code, ext_int_handler_t handler)

{

	struct ext_int_info *p;

	unsigned long flags;

	int index;



	p = kmalloc(sizeof(*p), GFP_ATOMIC);
@@ -174,33 +182,27 @@ int register_external_interrupt(u16 code, ext_int_handler_t handler) 
	p->code = code;

	p->handler = handler;

	index = ext_hash(code);

	p->next = ext_int_hash[index];

	ext_int_hash[index] = p;



	spin_lock_irqsave(&ext_int_hash_lock, flags);

	list_add_rcu(&p->entry, &ext_int_hash[index]);

	spin_unlock_irqrestore(&ext_int_hash_lock, flags);

	return 0;

}

EXPORT_SYMBOL(register_external_interrupt);



int unregister_external_interrupt(u16 code, ext_int_handler_t handler)

{

	struct ext_int_info *p, *q;

	int index;

	struct ext_int_info *p;

	unsigned long flags;

	int index = ext_hash(code);



	index = ext_hash(code);

	q = NULL;

	p = ext_int_hash[index];

	while (p) {

		if (p->code == code && p->handler == handler)

			break;

		q = p;

		p = p->next;

	spin_lock_irqsave(&ext_int_hash_lock, flags);

	list_for_each_entry_rcu(p, &ext_int_hash[index], entry)

		if (p->code == code && p->handler == handler) {

			list_del_rcu(&p->entry);

			call_rcu(&p->rcu, ext_int_hash_update);

		}

	if (!p)

		return -ENOENT;

	if (q)

		q->next = p->next;

	else

		ext_int_hash[index] = p->next;

	kfree(p);

	spin_unlock_irqrestore(&ext_int_hash_lock, flags);

	return 0;

}

EXPORT_SYMBOL(unregister_external_interrupt);
@@ -224,15 +226,22 @@ void __irq_entry do_extint(struct pt_regs *regs, unsigned int ext_int_code, 
	kstat_cpu(smp_processor_id()).irqs[EXTERNAL_INTERRUPT]++;

	if (code != 0x1004)

		__get_cpu_var(s390_idle).nohz_delay = 1;



	index = ext_hash(code);

	for (p = ext_int_hash[index]; p; p = p->next) {

	rcu_read_lock();

	list_for_each_entry_rcu(p, &ext_int_hash[index], entry)

		if (likely(p->code == code))

			p->handler(ext_int_code, param32, param64);

	}

	rcu_read_unlock();

	irq_exit();

	set_irq_regs(old_regs);

}



void __init init_IRQ(void)

{

	init_external_interrupts();

}



static DEFINE_SPINLOCK(sc_irq_lock);

static int sc_irq_refcount;