Commit b5470dc5 authored by Dan Williams's avatar Dan Williams
Browse files

md: resolve external metadata handling deadlock in md_allow_write 



md_allow_write() marks the metadata dirty while holding mddev->lock and then
waits for the write to complete.  For externally managed metadata this causes a
deadlock as userspace needs to take the lock to communicate that the metadata
update has completed.

Change md_allow_write() in the 'external' case to start the 'mark active'
operation and then return -EAGAIN.  The expected side effects while waiting for
userspace to write 'active' to 'array_state' are holding off reshape (code
currently handles -ENOMEM), cause some 'stripe_cache_size' change requests to
fail, cause some GET_BITMAP_FILE ioctl requests to fall back to GFP_NOIO, and
cause updates to 'raid_disks' to fail.  Except for 'stripe_cache_size' changes
these failures can be mitigated by coordinating with mdmon.

md_write_start() still prevents writes from occurring until the metadata
handler has had a chance to take action as it unconditionally waits for
MD_CHANGE_CLEAN to be cleared.

[neilb@suse.de: return -EAGAIN, try GFP_NOIO]
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
parent 1fe797e6

drivers/md/md.c

+16 −11
Original line number Diff line number Diff line
@@ -4172,9 +4172,11 @@ static int get_bitmap_file(mddev_t * mddev, void __user * arg) 
	char *ptr, *buf = NULL;

	int err = -ENOMEM;



	md_allow_write(mddev);



	if (md_allow_write(mddev))

		file = kmalloc(sizeof(*file), GFP_NOIO);

	else

		file = kmalloc(sizeof(*file), GFP_KERNEL);



	if (!file)

		goto out;
@@ -5667,15 +5669,18 @@ void md_write_end(mddev_t *mddev) 
 * may proceed without blocking.  It is important to call this before

 * attempting a GFP_KERNEL allocation while holding the mddev lock.

 * Must be called with mddev_lock held.

 *

 * In the ->external case MD_CHANGE_CLEAN can not be cleared until mddev->lock

 * is dropped, so return -EAGAIN after notifying userspace.

 */

void md_allow_write(mddev_t *mddev)

int md_allow_write(mddev_t *mddev)

{

	if (!mddev->pers)

		return;

		return 0;

	if (mddev->ro)

		return;

		return 0;

	if (!mddev->pers->sync_request)

		return;

		return 0;



	spin_lock_irq(&mddev->write_lock);

	if (mddev->in_sync) {
@@ -5686,14 +5691,14 @@ void md_allow_write(mddev_t *mddev) 
			mddev->safemode = 1;

		spin_unlock_irq(&mddev->write_lock);

		md_update_sb(mddev, 0);



		sysfs_notify(&mddev->kobj, NULL, "array_state");

		/* wait for the dirty state to be recorded in the metadata */

		wait_event(mddev->sb_wait,

			   !test_bit(MD_CHANGE_CLEAN, &mddev->flags) &&

			   !test_bit(MD_CHANGE_PENDING, &mddev->flags));

	} else

		spin_unlock_irq(&mddev->write_lock);



	if (test_bit(MD_CHANGE_CLEAN, &mddev->flags))

		return -EAGAIN;

	else

		return 0;

}

EXPORT_SYMBOL_GPL(md_allow_write);

drivers/md/raid1.c

+4 −2
Original line number Diff line number Diff line
@@ -2136,7 +2136,7 @@ static int raid1_reshape(mddev_t *mddev) 
	conf_t *conf = mddev_to_conf(mddev);

	int cnt, raid_disks;

	unsigned long flags;

	int d, d2;

	int d, d2, err;



	/* Cannot change chunk_size, layout, or level */

	if (mddev->chunk_size != mddev->new_chunk ||
@@ -2148,7 +2148,9 @@ static int raid1_reshape(mddev_t *mddev) 
		return -EINVAL;

	}



	md_allow_write(mddev);

	err = md_allow_write(mddev);

	if (err)

		return err;



	raid_disks = mddev->raid_disks + mddev->delta_disks;

drivers/md/raid5.c

+9 −3
Original line number Diff line number Diff line
@@ -911,14 +911,16 @@ static int resize_stripes(raid5_conf_t *conf, int newsize) 
	struct stripe_head *osh, *nsh;

	LIST_HEAD(newstripes);

	struct disk_info *ndisks;

	int err = 0;

	int err;

	struct kmem_cache *sc;

	int i;



	if (newsize <= conf->pool_size)

		return 0; /* never bother to shrink */



	md_allow_write(conf->mddev);

	err = md_allow_write(conf->mddev);

	if (err)

		return err;



	/* Step 1 */

	sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
@@ -3843,6 +3845,8 @@ raid5_store_stripe_cache_size(mddev_t *mddev, const char *page, size_t len) 
{

	raid5_conf_t *conf = mddev_to_conf(mddev);

	unsigned long new;

	int err;



	if (len >= PAGE_SIZE)

		return -EINVAL;

	if (!conf)
@@ -3858,7 +3862,9 @@ raid5_store_stripe_cache_size(mddev_t *mddev, const char *page, size_t len) 
		else

			break;

	}

	md_allow_write(mddev);

	err = md_allow_write(mddev);

	if (err)

		return err;

	while (new > conf->max_nr_stripes) {

		if (grow_one_stripe(conf))

			conf->max_nr_stripes++;

include/linux/raid/md.h

+1 −1
Original line number Diff line number Diff line
@@ -95,7 +95,7 @@ extern int sync_page_io(struct block_device *bdev, sector_t sector, int size, 
			struct page *page, int rw);

extern void md_do_sync(mddev_t *mddev);

extern void md_new_event(mddev_t *mddev);

extern void md_allow_write(mddev_t *mddev);

extern int md_allow_write(mddev_t *mddev);

extern void md_wait_for_blocked_rdev(mdk_rdev_t *rdev, mddev_t *mddev);



#endif /* CONFIG_MD */

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