[dm-devel] [PATCH 2/7] multipathd: fix check_path errors with removed map

[Martin Wilck]

On Thu, 2020-06-18 at 18:17 -0500, Benjamin Marzinski wrote:
> On Thu, Jun 18, 2020 at 07:34:38PM +0000, Martin Wilck wrote:
> > On Wed, 2020-06-17 at 19:24 -0500, Benjamin Marzinski wrote:
> > > 
> > >  static void
> > > @@ -2088,8 +2084,13 @@ check_path (struct vectors * vecs, struct
> > > path
> > > * pp, unsigned int ticks)
> > >  	 * Synchronize with kernel state
> > >  	 */
> > >  	if (update_multipath_strings(pp->mpp, vecs->pathvec, 1)) {
> > > +		struct dm_info info;
> > >  		condlog(1, "%s: Could not synchronize with kernel
> > > state",
> > >  			pp->dev);
> > > +		if (pp->mpp && pp->mpp->alias &&
> > > +		    do_dm_get_info(pp->mpp->alias, &info) == 0)
> > > +			/* multipath device missing. Likely removed */
> > > +			return 0;
> > >  		pp->dmstate = PSTATE_UNDEF;
> > 
> > It would be more elegant if we could distinguish different failure
> > modes from update_multipath_strings() directly, without having to
> > call
> > do_dm_get_info() again.
> 
> Seems reasonable. I'll take a look at that.

Yet another idea: I just discussed this with Hannes, and he pointed out
that right below this code, we have

	/* if update_multipath_strings orphaned the path, quit early */
	if (!pp->mpp)
		return 0;

... which could have the same effect, if pp->mpp was reloaded. Probably
that doesn't happen because the pp->mpp dereference is cached in a
register, but we could simply add a READ_ONCE there.

Choose what you prefer.

Regards,
Martin

-- 
Dr. Martin Wilck <mwilck at suse.com>, Tel. +49 (0)911 74053 2107
SUSE  Software Solutions Germany GmbH
HRB 36809, AG Nürnberg GF: Felix
Imendörffer