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Commit e804ac78 authored by Tejun Heo's avatar Tejun Heo Committed by NeilBrown
Browse files

md: fix and update workqueue usage 



Workqueue usage in md has two problems.

* Flush can be used during or depended upon by memory reclaim, but md
  uses the system workqueue for flush_work which may lead to deadlock.

* md depends on flush_scheduled_work() to achieve exclusion against
  completion of removal of previous instances.  flush_scheduled_work()
  may incur unexpected amount of delay and is scheduled to be removed.

This patch adds two workqueues to md - md_wq and md_misc_wq.  The
former is guaranteed to make forward progress under memory pressure
and serves flush_work.  The latter serves as the flush domain for
other works.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent 57dab0bd

drivers/md/md.c

+43 −21
Original line number Diff line number Diff line
@@ -67,6 +67,8 @@ static DEFINE_SPINLOCK(pers_lock); 
static void md_print_devices(void);



static DECLARE_WAIT_QUEUE_HEAD(resync_wait);

static struct workqueue_struct *md_wq;

static struct workqueue_struct *md_misc_wq;



#define MD_BUG(x...) { printk("md: bug in file %s, line %d\n", __FILE__, __LINE__); md_print_devices(); }
@@ -298,7 +300,7 @@ static void md_end_flush(struct bio *bio, int err) 


	if (atomic_dec_and_test(&mddev->flush_pending)) {

		/* The pre-request flush has finished */

		schedule_work(&mddev->flush_work);

		queue_work(md_wq, &mddev->flush_work);

	}

	bio_put(bio);

}
@@ -367,7 +369,7 @@ void md_flush_request(mddev_t *mddev, struct bio *bio) 
	submit_flushes(mddev);



	if (atomic_dec_and_test(&mddev->flush_pending))

		schedule_work(&mddev->flush_work);

		queue_work(md_wq, &mddev->flush_work);

}

EXPORT_SYMBOL(md_flush_request);
@@ -434,14 +436,13 @@ static void mddev_put(mddev_t *mddev) 
		 * so destroy it */

		list_del(&mddev->all_mddevs);

		if (mddev->gendisk) {

			/* we did a probe so need to clean up.

			 * Call schedule_work inside the spinlock

			 * so that flush_scheduled_work() after

			 * mddev_find will succeed in waiting for the

			 * work to be done.

			/* We did a probe so need to clean up.  Call

			 * queue_work inside the spinlock so that

			 * flush_workqueue() after mddev_find will

			 * succeed in waiting for the work to be done.

			 */

			INIT_WORK(&mddev->del_work, mddev_delayed_delete);

			schedule_work(&mddev->del_work);

			queue_work(md_misc_wq, &mddev->del_work);

		} else

			kfree(mddev);

	}
@@ -1848,7 +1849,7 @@ static void unbind_rdev_from_array(mdk_rdev_t * rdev) 
	synchronize_rcu();

	INIT_WORK(&rdev->del_work, md_delayed_delete);

	kobject_get(&rdev->kobj);

	schedule_work(&rdev->del_work);

	queue_work(md_misc_wq, &rdev->del_work);

}



/*
@@ -4192,10 +4193,10 @@ static int md_alloc(dev_t dev, char *name) 
	shift = partitioned ? MdpMinorShift : 0;

	unit = MINOR(mddev->unit) >> shift;



	/* wait for any previous instance if this device

	 * to be completed removed (mddev_delayed_delete).

	/* wait for any previous instance of this device to be

	 * completely removed (mddev_delayed_delete).

	 */

	flush_scheduled_work();

	flush_workqueue(md_misc_wq);



	mutex_lock(&disks_mutex);

	error = -EEXIST;
@@ -5891,7 +5892,7 @@ static int md_open(struct block_device *bdev, fmode_t mode) 
		 */

		mddev_put(mddev);

		/* Wait until bdev->bd_disk is definitely gone */

		flush_scheduled_work();

		flush_workqueue(md_misc_wq);

		/* Then retry the open from the top */

		return -ERESTARTSYS;

	}
@@ -6047,7 +6048,7 @@ void md_error(mddev_t *mddev, mdk_rdev_t *rdev) 
	set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);

	md_wakeup_thread(mddev->thread);

	if (mddev->event_work.func)

		schedule_work(&mddev->event_work);

		queue_work(md_misc_wq, &mddev->event_work);

	md_new_event_inintr(mddev);

}
@@ -7207,12 +7208,23 @@ static void md_geninit(void) 


static int __init md_init(void)

{

	if (register_blkdev(MD_MAJOR, "md"))

		return -1;

	if ((mdp_major=register_blkdev(0, "mdp"))<=0) {

		unregister_blkdev(MD_MAJOR, "md");

		return -1;

	}

	int ret = -ENOMEM;



	md_wq = alloc_workqueue("md", WQ_RESCUER, 0);

	if (!md_wq)

		goto err_wq;



	md_misc_wq = alloc_workqueue("md_misc", 0, 0);

	if (!md_misc_wq)

		goto err_misc_wq;



	if ((ret = register_blkdev(MD_MAJOR, "md")) < 0)

		goto err_md;



	if ((ret = register_blkdev(0, "mdp")) < 0)

		goto err_mdp;

	mdp_major = ret;



	blk_register_region(MKDEV(MD_MAJOR, 0), 1UL<<MINORBITS, THIS_MODULE,

			    md_probe, NULL, NULL);

	blk_register_region(MKDEV(mdp_major, 0), 1UL<<MINORBITS, THIS_MODULE,
@@ -7223,8 +7235,16 @@ static int __init md_init(void) 


	md_geninit();

	return 0;

}



err_mdp:

	unregister_blkdev(MD_MAJOR, "md");

err_md:

	destroy_workqueue(md_misc_wq);

err_misc_wq:

	destroy_workqueue(md_wq);

err_wq:

	return ret;

}



#ifndef MODULE
@@ -7311,6 +7331,8 @@ static __exit void md_exit(void) 
		export_array(mddev);

		mddev->hold_active = 0;

	}

	destroy_workqueue(md_misc_wq);

	destroy_workqueue(md_wq);

}



subsys_initcall(md_init);