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Commit 48cae885 authored by Stefan Weinhuber's avatar Stefan Weinhuber Committed by Martin Schwidefsky
Browse files

[S390] dasd: fix race in dasd timer handling 



In dasd_device_set_timer and dasd_block_set_timer we interpret the
return value of mod_timer in a wrong way. If the timer expires in
the small window between our check of timer_pending and the call to
mod_timer, then the timer will be set, mod_timer returns zero and
we will call add_timer for a timer that is already pending.
As del_timer and mod_timer do all the necessary checking themselves,
we can simplify our code and remove the race a the same time.

Signed-off-by: default avatarStefan Weinhuber <wein@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent ca0b4b7d

drivers/s390/block/dasd.c

+16 −30
Original line number Diff line number Diff line
@@ -57,6 +57,8 @@ static void dasd_device_tasklet(struct dasd_device *); 
static void dasd_block_tasklet(struct dasd_block *);

static void do_kick_device(struct work_struct *);

static void dasd_return_cqr_cb(struct dasd_ccw_req *, void *);

static void dasd_device_timeout(unsigned long);

static void dasd_block_timeout(unsigned long);



/*

 * SECTION: Operations on the device structure.
@@ -99,6 +101,8 @@ struct dasd_device *dasd_alloc_device(void) 
		     (unsigned long) device);

	INIT_LIST_HEAD(&device->ccw_queue);

	init_timer(&device->timer);

	device->timer.function = dasd_device_timeout;

	device->timer.data = (unsigned long) device;

	INIT_WORK(&device->kick_work, do_kick_device);

	device->state = DASD_STATE_NEW;

	device->target = DASD_STATE_NEW;
@@ -138,6 +142,8 @@ struct dasd_block *dasd_alloc_block(void) 
	INIT_LIST_HEAD(&block->ccw_queue);

	spin_lock_init(&block->queue_lock);

	init_timer(&block->timer);

	block->timer.function = dasd_block_timeout;

	block->timer.data = (unsigned long) block;



	return block;

}
@@ -915,19 +921,10 @@ static void dasd_device_timeout(unsigned long ptr) 
 */

void dasd_device_set_timer(struct dasd_device *device, int expires)

{

	if (expires == 0) {

		if (timer_pending(&device->timer))

	if (expires == 0)

		del_timer(&device->timer);

		return;

	}

	if (timer_pending(&device->timer)) {

		if (mod_timer(&device->timer, jiffies + expires))

			return;

	}

	device->timer.function = dasd_device_timeout;

	device->timer.data = (unsigned long) device;

	device->timer.expires = jiffies + expires;

	add_timer(&device->timer);

	else

		mod_timer(&device->timer, jiffies + expires);

}



/*
@@ -935,7 +932,6 @@ void dasd_device_set_timer(struct dasd_device *device, int expires) 
 */

void dasd_device_clear_timer(struct dasd_device *device)

{

	if (timer_pending(&device->timer))

	del_timer(&device->timer);

}
@@ -1586,19 +1582,10 @@ static void dasd_block_timeout(unsigned long ptr) 
 */

void dasd_block_set_timer(struct dasd_block *block, int expires)

{

	if (expires == 0) {

		if (timer_pending(&block->timer))

	if (expires == 0)

		del_timer(&block->timer);

		return;

	}

	if (timer_pending(&block->timer)) {

		if (mod_timer(&block->timer, jiffies + expires))

			return;

	}

	block->timer.function = dasd_block_timeout;

	block->timer.data = (unsigned long) block;

	block->timer.expires = jiffies + expires;

	add_timer(&block->timer);

	else

		mod_timer(&block->timer, jiffies + expires);

}



/*
@@ -1606,7 +1593,6 @@ void dasd_block_set_timer(struct dasd_block *block, int expires) 
 */

void dasd_block_clear_timer(struct dasd_block *block)

{

	if (timer_pending(&block->timer))

	del_timer(&block->timer);

}