On Thu, Feb 26 2015 at 11:41am -0500, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > There was a bug when that resulted in a crash when there were pending > exceptions and snapshot exception store handover was performed at the > same time - and there was a patch that fixed it. > > 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 it's associated md. > > To avoid lockdep warnings, the target must be suspended and resumed > without holding _origins_lock. > > This patch introduces a function dm_hold that grabs a reference on > mapped_device, but unlike dm_get, it doesn't crash if the devices has the > flag DMF_FREEING, it returns and 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. > > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> Staged for 4.0 here (again bumped target version and tweaked header): https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-for-4.0&id=09ee96b21456883e108c3b00597bb37ec512151b > Index: linux-2.6-debug/drivers/md/dm.c > =================================================================== > --- linux-2.6-debug.orig/drivers/md/dm.c > +++ linux-2.6-debug/drivers/md/dm.c > @@ -2526,10 +2539,16 @@ static void __dm_destroy(struct mapped_d > set_bit(DMF_FREEING, &md->flags); > spin_unlock(&_minor_lock); > > + /* > + * Take suspend_lock so that presuspend and postsuspend methods > + * do not race with internal suspend. > + */ > + mutex_lock(&md->suspend_lock); > if (!dm_suspended_md(md)) { > dm_table_presuspend_targets(map); > dm_table_postsuspend_targets(map); > } > + mutex_unlock(&md->suspend_lock); > > /* dm_put_live_table must be before msleep, otherwise deadlock is possible */ > dm_put_live_table(md, srcu_idx); I split this chunk out to a new commit for 4.0 here: https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-for-4.0&id=ab7c7bb6f4ab95dbca96fcfc4463cd69843e3e24 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
