From: Kiyoshi Ueda Remove the dm_get() in dm_table_get_md() because dm_table_get_md() could be called from presuspend/postsuspend, which are called while mapped_device is in DMF_FREEING state, where dm_get() is not allowed. Justification for that is the lifetime of both objects: As far as the current dm design/implementation, mapped_device is never freed while targets are doing something, because dm core waits for targets to become quiet in dm_put() using presuspend/postsuspend. So targets should be able to touch mapped_device without holding reference count of the mapped_device, and we should allow targets to touch mapped_device even if it is in DMF_FREEING state. Backgrounds: I'm trying to remove the multipath internal queue, since dm core now has a generic queue for request-based dm. In the patch-set, the multipath target wants to request dm core to start/stop queue. One of such start/stop requests can happen during postsuspend() while the target waits for pg-init to complete, because the target stops queue when starting pg-init and tries to restart it when completing pg-init. Since queue belongs to mapped_device, it involves calling dm_table_get_md() and dm_put(). On the other hand, postsuspend() is called in dm_put() for mapped_device which is in DMF_FREEING state, and that triggers BUG_ON(DMF_FREEING) in the 2nd dm_put(). I had tried to solve this problem by changing only multipath not to touch mapped_device which is in DMF_FREEING state, but I couldn't and I came up with a question why we need dm_get() in dm_table_get_md(). Signed-off-by: Kiyoshi Ueda Signed-off-by: Jun'ichi Nomura Signed-off-by: Alasdair G Kergon --- drivers/md/dm-table.c | 2 -- drivers/md/dm-uevent.c | 7 ++----- drivers/md/dm.c | 14 ++------------ 3 files changed, 4 insertions(+), 19 deletions(-) Index: linux-2.6.33/drivers/md/dm-table.c =================================================================== --- linux-2.6.33.orig/drivers/md/dm-table.c +++ linux-2.6.33/drivers/md/dm-table.c @@ -1231,8 +1231,6 @@ void dm_table_unplug_all(struct dm_table struct mapped_device *dm_table_get_md(struct dm_table *t) { - dm_get(t->md); - return t->md; } Index: linux-2.6.33/drivers/md/dm-uevent.c =================================================================== --- linux-2.6.33.orig/drivers/md/dm-uevent.c +++ linux-2.6.33/drivers/md/dm-uevent.c @@ -187,7 +187,7 @@ void dm_path_uevent(enum dm_uevent_type if (event_type >= ARRAY_SIZE(_dm_uevent_type_names)) { DMERR("%s: Invalid event_type %d", __func__, event_type); - goto out; + return; } event = dm_build_path_uevent(md, ti, @@ -195,12 +195,9 @@ void dm_path_uevent(enum dm_uevent_type _dm_uevent_type_names[event_type].name, path, nr_valid_paths); if (IS_ERR(event)) - goto out; + return; dm_uevent_add(md, &event->elist); - -out: - dm_put(md); } EXPORT_SYMBOL_GPL(dm_path_uevent); Index: linux-2.6.33/drivers/md/dm.c =================================================================== --- linux-2.6.33.orig/drivers/md/dm.c +++ linux-2.6.33/drivers/md/dm.c @@ -2699,23 +2699,13 @@ int dm_suspended_md(struct mapped_device int dm_suspended(struct dm_target *ti) { - struct mapped_device *md = dm_table_get_md(ti->table); - int r = dm_suspended_md(md); - - dm_put(md); - - return r; + return dm_suspended_md(dm_table_get_md(ti->table)); } EXPORT_SYMBOL_GPL(dm_suspended); int dm_noflush_suspending(struct dm_target *ti) { - struct mapped_device *md = dm_table_get_md(ti->table); - int r = __noflush_suspending(md); - - dm_put(md); - - return r; + return __noflush_suspending(dm_table_get_md(ti->table)); } EXPORT_SYMBOL_GPL(dm_noflush_suspending);