This is backport of 09ee96b21456883e108c3b00597bb37ec512151b for 3.10 and 3.14.
commit 09ee96b21456883e108c3b00597bb37ec512151b Author: Mikulas Patocka <[email protected]> Date: Thu Feb 26 11:41:28 2015 -0500 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: Mikulas Patocka <[email protected]> Signed-off-by: Mike Snitzer <[email protected]> Cc: [email protected] --- drivers/md/dm-snap.c | 39 +++++++++++++++++++++++++++++++-------- drivers/md/dm.c | 13 +++++++++++++ include/linux/device-mapper.h | 1 + 3 files changed, 45 insertions(+), 8 deletions(-) Index: linux-stable/drivers/md/dm-snap.c =================================================================== --- linux-stable.orig/drivers/md/dm-snap.c 2015-06-02 18:34:42.000000000 +0200 +++ linux-stable/drivers/md/dm-snap.c 2015-06-02 18:36:01.000000000 +0200 @@ -1895,20 +1895,39 @@ static int snapshot_preresume(struct dm_ 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 == dm_table_get_md(ti->table)) - origin_md = NULL; + 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; + } + + up_read(&_origins_lock); - if (origin_md) + 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) { @@ -1919,11 +1938,15 @@ static void snapshot_resume(struct dm_ta 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); @@ -2356,7 +2379,7 @@ static struct target_type snapshot_targe 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, Index: linux-stable/drivers/md/dm.c =================================================================== --- linux-stable.orig/drivers/md/dm.c 2015-06-02 18:34:42.000000000 +0200 +++ linux-stable/drivers/md/dm.c 2015-06-02 18:35:24.000000000 +0200 @@ -2333,6 +2333,19 @@ 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; Index: linux-stable/include/linux/device-mapper.h =================================================================== --- linux-stable.orig/include/linux/device-mapper.h 2015-06-02 18:34:42.000000000 +0200 +++ linux-stable/include/linux/device-mapper.h 2015-06-02 18:35:24.000000000 +0200 @@ -373,6 +373,7 @@ int dm_create(int minor, struct mapped_d */ 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); /* -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
