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Commit 12c2bdb2 authored by Derek Basehore's avatar Derek Basehore Committed by Jens Axboe
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block: prevent race/cleanup 



Remove a race condition which causes a warning in disk_clear_events.  This
is a race between disk_clear_events() and disk_flush_events().
ev->clearing will be altered by disk_flush_events() even though we are
blocking event checking through disk_flush_events().  If this happens
after ev->clearing was cleared for disk_clear_events(), this can cause the
WARN_ON_ONCE() in that function to be triggered.

This change also has disk_clear_events() not go through a workqueue.
Since we have to wait for the work to complete, we should just call the
function directly.  Also, since this work cannot be put on a freezable
workqueue, it will have to contend with increased demand, so calling the
function directly avoids this.

[akpm@linux-foundation.org: fix spello in comment]
Signed-off-by: default avatarDerek Basehore <dbasehore@chromium.org>
Cc: Mandeep Singh Baines <msb@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent aea24a8b

block/genhd.c

+30 −15
Original line number Diff line number Diff line
@@ -35,6 +35,8 @@ static DEFINE_IDR(ext_devt_idr); 


static struct device_type disk_type;



static void disk_check_events(struct disk_events *ev,

			      unsigned int *clearing_ptr);

static void disk_alloc_events(struct gendisk *disk);

static void disk_add_events(struct gendisk *disk);

static void disk_del_events(struct gendisk *disk);
@@ -1549,6 +1551,7 @@ unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask) 
	const struct block_device_operations *bdops = disk->fops;

	struct disk_events *ev = disk->ev;

	unsigned int pending;

	unsigned int clearing = mask;



	if (!ev) {

		/* for drivers still using the old ->media_changed method */
@@ -1558,41 +1561,53 @@ unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask) 
		return 0;

	}



	/* tell the workfn about the events being cleared */

	disk_block_events(disk);



	/*

	 * store the union of mask and ev->clearing on the stack so that the

	 * race with disk_flush_events does not cause ambiguity (ev->clearing

	 * can still be modified even if events are blocked).

	 */

	spin_lock_irq(&ev->lock);

	ev->clearing |= mask;

	clearing |= ev->clearing;

	ev->clearing = 0;

	spin_unlock_irq(&ev->lock);



	/* uncondtionally schedule event check and wait for it to finish */

	disk_block_events(disk);

	disk_check_events(ev, &clearing);

	/*

	 * We need to put the work on system_nrt_wq here since there is a

	 * deadlock that happens while probing a usb device while suspending. If

	 * we put work on a freezable workqueue here, a usb probe will wait here

	 * until the workqueue is unfrozen during suspend. Since suspend waits

	 * on all probes to complete, we have a deadlock

	 * if ev->clearing is not 0, the disk_flush_events got called in the

	 * middle of this function, so we want to run the workfn without delay.

	 */

	queue_delayed_work(system_nrt_wq, &ev->dwork, 0);

	flush_delayed_work(&ev->dwork);

	__disk_unblock_events(disk, false);

	__disk_unblock_events(disk, ev->clearing ? true : false);



	/* then, fetch and clear pending events */

	spin_lock_irq(&ev->lock);

	WARN_ON_ONCE(ev->clearing & mask);	/* cleared by workfn */

	pending = ev->pending & mask;

	ev->pending &= ~mask;

	spin_unlock_irq(&ev->lock);

	WARN_ON_ONCE(clearing & mask);



	return pending;

}



/*

 * Separate this part out so that a different pointer for clearing_ptr can be

 * passed in for disk_clear_events.

 */

static void disk_events_workfn(struct work_struct *work)

{

	struct delayed_work *dwork = to_delayed_work(work);

	struct disk_events *ev = container_of(dwork, struct disk_events, dwork);



	disk_check_events(ev, &ev->clearing);

}



static void disk_check_events(struct disk_events *ev,

			      unsigned int *clearing_ptr)

{

	struct gendisk *disk = ev->disk;

	char *envp[ARRAY_SIZE(disk_uevents) + 1] = { };

	unsigned int clearing = ev->clearing;

	unsigned int clearing = *clearing_ptr;

	unsigned int events;

	unsigned long intv;

	int nr_events = 0, i;
@@ -1605,7 +1620,7 @@ static void disk_events_workfn(struct work_struct *work) 


	events &= ~ev->pending;

	ev->pending |= events;

	ev->clearing &= ~clearing;

	*clearing_ptr &= ~clearing;



	intv = disk_events_poll_jiffies(disk);

	if (!ev->block && intv)