Commit d07b953a authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Luis Henriques

dm snapshot: suspend merging snapshot when doing exception handover

commit 09ee96b2 upstream.

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>
[ luis: backported to 3.16: as suggested by the author:
  - replaced dm_internal_suspend_fast by dm_internal_suspend
  - replaced dm_internal_resume_fast by dm_internal_resume ]
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 945c463b
......@@ -1896,20 +1896,39 @@ 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(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) {
......@@ -1920,11 +1939,15 @@ static void snapshot_resume(struct dm_target *ti)
up_write(&snap_src->lock);
}
if (origin_md)
dm_internal_resume(origin_md);
up_read(&_origins_lock);
if (origin_md) {
if (must_restart_merging)
start_merge(snap_merging);
dm_internal_resume(origin_md);
dm_put(origin_md);
}
/* Now we have correct chunk size, reregister */
reregister_snapshot(s);
......@@ -2368,7 +2391,7 @@ 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,
......
......@@ -2386,6 +2386,19 @@ 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;
......
......@@ -366,6 +366,7 @@ 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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