Commit ecdb2e25 authored Mar 06, 2010 by Kiyoshi Ueda Committed by Alasdair G Kergon Mar 06, 2010

dm table: remove dm_get from dm_table_get_md

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 <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

parent f7b934c8

drivers/md/dm-table.c

+0 −2

Original line number	Diff line number	Diff line
		@@ -1231,8 +1231,6 @@ void dm_table_unplug_all(struct dm_table *t)

		struct mapped_device dm_table_get_md(struct dm_table t)
		{
		dm_get(t->md);

		return t->md;
		}

drivers/md/dm-uevent.c

+2 −5

Original line number	Diff line number	Diff line
		@@ -187,7 +187,7 @@ void dm_path_uevent(enum dm_uevent_type event_type, struct dm_target *ti,

		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 event_type, struct dm_target *ti,
		_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);

drivers/md/dm.c

+2 −12

Original line number	Diff line number	Diff line
		@@ -2699,23 +2699,13 @@ int dm_suspended_md(struct mapped_device *md)

		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);

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