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Commit 0eb69a0c authored by Sebastian Ott's avatar Sebastian Ott Committed by Martin Schwidefsky
Browse files

s390/airq: silence lockdep warning 



airq_iv_(alloc|free) is called by some users with interrupts enabled
and by some with interrupts disabled which leads to the following
lockdep warning:

[ INFO: possible irq lock inversion dependency detected ]
3.14.0-15249-gbf29b7b-dirty #25 Not tainted
---------------------------------------------------------
insmod/2108 just changed the state of lock:
 (&(&iv->lock)->rlock){+.....}, at: [<000000000046ee3e>] airq_iv_alloc+0x62/0x228
but this lock was taken by another, HARDIRQ-READ-safe lock in the past:
 (&info->lock){.-.-..}

and interrupts could create inverse lock ordering between them.

other info that might help us debug this:
 Possible interrupt unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&(&iv->lock)->rlock);
                               local_irq_disable();
                               lock(&info->lock);
                               lock(&(&iv->lock)->rlock);
  <Interrupt>
    lock(&info->lock);

 *** DEADLOCK ***

Although this is a false alarm (since each airq user consistently
calls these functions from the same context) fix this by ensuring
that interrupts are disabled when the airq lock is held.

Reported-by: default avatarFrank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: default avatarSebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 646f919e

drivers/s390/cio/airq.c

+6 −7
Original line number Diff line number Diff line
@@ -196,11 +196,11 @@ EXPORT_SYMBOL(airq_iv_release); 
 */

unsigned long airq_iv_alloc(struct airq_iv *iv, unsigned long num)

{

	unsigned long bit, i;

	unsigned long bit, i, flags;



	if (!iv->avail || num == 0)

		return -1UL;

	spin_lock(&iv->lock);

	spin_lock_irqsave(&iv->lock, flags);

	bit = find_first_bit_inv(iv->avail, iv->bits);

	while (bit + num <= iv->bits) {

		for (i = 1; i < num; i++)
@@ -218,9 +218,8 @@ unsigned long airq_iv_alloc(struct airq_iv *iv, unsigned long num) 
	}

	if (bit + num > iv->bits)

		bit = -1UL;

	spin_unlock(&iv->lock);

	spin_unlock_irqrestore(&iv->lock, flags);

	return bit;



}

EXPORT_SYMBOL(airq_iv_alloc);
@@ -232,11 +231,11 @@ EXPORT_SYMBOL(airq_iv_alloc); 
 */

void airq_iv_free(struct airq_iv *iv, unsigned long bit, unsigned long num)

{

	unsigned long i;

	unsigned long i, flags;



	if (!iv->avail || num == 0)

		return;

	spin_lock(&iv->lock);

	spin_lock_irqsave(&iv->lock, flags);

	for (i = 0; i < num; i++) {

		/* Clear (possibly left over) interrupt bit */

		clear_bit_inv(bit + i, iv->vector);
@@ -248,7 +247,7 @@ void airq_iv_free(struct airq_iv *iv, unsigned long bit, unsigned long num) 
		while (iv->end > 0 && !test_bit_inv(iv->end - 1, iv->avail))

			iv->end--;

	}

	spin_unlock(&iv->lock);

	spin_unlock_irqrestore(&iv->lock, flags);

}

EXPORT_SYMBOL(airq_iv_free);