Commit 09ee96b2 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Mike Snitzer
Browse files

dm snapshot: suspend merging snapshot when doing exception handover 



The "dm snapshot: suspend origin when doing exception handover" commit
fixed a exception store handover bug associated with pending exceptions
to the "snapshot-origin" target.

However, a similar problem exists in snapshot merging.  When snapshot
merging is in progress, we use the target "snapshot-merge" instead of
"snapshot-origin".  Consequently, during exception store handover, we
must find the snapshot-merge target and suspend its associated
mapped_device.

To avoid lockdep warnings, the target must be suspended and resumed
without holding _origins_lock.

Introduce a dm_hold() function that grabs a reference on a
mapped_device, but unlike dm_get(), it doesn't crash if the device has
the DMF_FREEING flag set, it returns an error in this case.

In snapshot_resume() we grab the reference to the origin device using
dm_hold() while holding _origins_lock (_origins_lock guarantees that the
device won't disappear).  Then we release _origins_lock, suspend the
device and grab _origins_lock again.

NOTE to stable@ people:
When backporting to kernels 3.18 and older, use dm_internal_suspend and
dm_internal_resume instead of dm_internal_suspend_fast and
dm_internal_resume_fast.

Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
parent b735fede

drivers/md/dm-snap.c

+29 −6
Original line number Diff line number Diff line
@@ -1888,20 +1888,39 @@ static int snapshot_preresume(struct dm_target *ti) 
static void snapshot_resume(struct dm_target *ti)

{

	struct dm_snapshot *s = ti->private;

	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;

	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL, *snap_merging = NULL;

	struct dm_origin *o;

	struct mapped_device *origin_md = NULL;

	bool must_restart_merging = false;



	down_read(&_origins_lock);



	o = __lookup_dm_origin(s->origin->bdev);

	if (o)

		origin_md = dm_table_get_md(o->ti->table);

	if (!origin_md) {

		(void) __find_snapshots_sharing_cow(s, NULL, NULL, &snap_merging);

		if (snap_merging)

			origin_md = dm_table_get_md(snap_merging->ti->table);

	}

	if (origin_md == dm_table_get_md(ti->table))

		origin_md = NULL;

	if (origin_md) {

		if (dm_hold(origin_md))

			origin_md = NULL;

	}



	if (origin_md)

	up_read(&_origins_lock);



	if (origin_md) {

		dm_internal_suspend_fast(origin_md);

		if (snap_merging && test_bit(RUNNING_MERGE, &snap_merging->state_bits)) {

			must_restart_merging = true;

			stop_merge(snap_merging);

		}

	}



	down_read(&_origins_lock);



	(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);

	if (snap_src && snap_dest) {
@@ -1912,11 +1931,15 @@ static void snapshot_resume(struct dm_target *ti) 
		up_write(&snap_src->lock);

	}



	if (origin_md)

		dm_internal_resume_fast(origin_md);



	up_read(&_origins_lock);



	if (origin_md) {

		if (must_restart_merging)

			start_merge(snap_merging);

		dm_internal_resume_fast(origin_md);

		dm_put(origin_md);

	}



	/* Now we have correct chunk size, reregister */

	reregister_snapshot(s);
@@ -2360,7 +2383,7 @@ static struct target_type snapshot_target = { 


static struct target_type merge_target = {

	.name    = dm_snapshot_merge_target_name,

	.version = {1, 2, 0},

	.version = {1, 3, 0},

	.module  = THIS_MODULE,

	.ctr     = snapshot_ctr,

	.dtr     = snapshot_dtr,

drivers/md/dm.c

+13 −0
Original line number Diff line number Diff line
@@ -2616,6 +2616,19 @@ void dm_get(struct mapped_device *md) 
	BUG_ON(test_bit(DMF_FREEING, &md->flags));

}



int dm_hold(struct mapped_device *md)

{

	spin_lock(&_minor_lock);

	if (test_bit(DMF_FREEING, &md->flags)) {

		spin_unlock(&_minor_lock);

		return -EBUSY;

	}

	dm_get(md);

	spin_unlock(&_minor_lock);

	return 0;

}

EXPORT_SYMBOL_GPL(dm_hold);



const char *dm_device_name(struct mapped_device *md)

{

	return md->name;

include/linux/device-mapper.h

+1 −0
Original line number Diff line number Diff line
@@ -375,6 +375,7 @@ int dm_create(int minor, struct mapped_device **md); 
 */

struct mapped_device *dm_get_md(dev_t dev);

void dm_get(struct mapped_device *md);

int dm_hold(struct mapped_device *md);

void dm_put(struct mapped_device *md);



/*

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