On Mon, May 09, 2016 at 12:26:36PM +0200, Hannes Reinecke wrote: > On 05/06/2016 10:12 PM, Benjamin Marzinski wrote: > > On Wed, May 04, 2016 at 07:57:28AM +0200, Hannes Reinecke wrote: > >> libdevmapper has the 'quirk' that DM_DEVICE_CREATE is translated > >> internally into a create/load/resume sequence, and the associated > >> cookie will wait for the last 'resume' to complete. > >> However, DM_DEVICE_RELOAD has no such translation, so if there > >> is a cookie assigned to it the caller _cannot_ wait for it, > >> as the cookie will only ever be completed upon the next > >> DM_DEVICE_RESUME. > >> multipathd already has some provisions for that (but even there > >> the cookie handling is dodgy), but 'multipath -r' doesn't know > >> about this. > >> So to avoid any future irritations this patch updates the > >> dm_addmad_reload() call to handle the cookie correctly, > >> and removes the special handling from multipathd. > > > > I don't see what's multipathd specific about any of the handling here. > > The real answer is that device-mapper does nothing with cookies on > > table reload. We should never be calling dm_task_set_cookie() for > > dm_addmap(DM_DEVICE_RELOAD, ...) calls in the first place. We end up > > creating a cookie, decrementing the cookie, incrementing the cookie, and > > finally waiting on it, when we could just be creating a cookie and then > > waiting on it. > > > > It's kind of hard to find an easy to show example of this breaking. You > > would need to have the dm_addmap() command fail with some other error than > > EROFS. If that happens, the dm_simplecmd() call will never happen, and > > there will be a cookie sitting around on the system. If we never added > > a cookie to the task in dm_addmap(DM_DEVICE_RELOAD, ...), then there > > wouldn't be this cookie sitting around. > > > But then ... how is this supposed to work? > Are we supposed to call DM_DEVICE_RESUME even after DM_DEVICE_RELOAD > failed? > None of the other callers do that ... No. If we fail to load a new table, we do nothing, and the device continues as it is. If we don't ever call dm_task_set_cookie when we reload the table, then there is no cookie to wait for. And if loading a new table fails, then there is no new table to switch to, and no point in calling resume. -Ben > Cheers, > > Hannes > -- > Dr. Hannes Reinecke Teamlead Storage & Networking > hare@xxxxxxx +49 911 74053 688 > SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg > GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton > HRB 21284 (AG Nürnberg) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
