Re: [PATCH 03/13] multipathd: allow map removal in do_sync_mpp()

[Benjamin Marzinski <bmarzins@redhat.com>]

On Tue, Dec 10, 2024 at 02:02:32PM -0500, Benjamin Marzinski wrote:
> On Sat, Dec 07, 2024 at 12:36:07AM +0100, Martin Wilck wrote:
> > We previously didn't allow map removal inside the checker loop. But
> > with the late updates to the checkerloop code, it should be safe to orphan
> > paths and delete maps even in this situation. We remove such maps everywhere
> > else in the code already, whenever refresh_multipath() or setup_multipath()
> > is called.
> 
> I don't think that this is safe. It's possible that the multipath device
> has paths in the INIT_REMOVED or INIT_PARTIAL state. These will get
> silently removed from the pathvec if we remove the map here. This will
> mess up our iteration through the pathvec in update_paths(). Perhaps a
> better idea would be to set mpp->sync_ticks to 0 if
> update_multipath_strings() fails in do_sync_mpp(). This would force a
> refresh by sync_mpp() at the start of the next loop in checkerloop(),
> where it can safely remove the multipath device.

If we go this route we should probably rename do_sync_map() to
sync_map() and rename sync_map() to something like check_refresh_map(),
since it would now be calling refresh_map() instead of do_sync_map().

> 
> -Ben
>  
> > Signed-off-by: Martin Wilck <mwilck@suse.com>
> > ---
> >  multipathd/main.c | 43 ++++++++++++++++++++-----------------------
> >  1 file changed, 20 insertions(+), 23 deletions(-)
> > 
> > diff --git a/multipathd/main.c b/multipathd/main.c
> > index 4a28fbb..131dab6 100644
> > --- a/multipathd/main.c
> > +++ b/multipathd/main.c
> > @@ -2446,34 +2446,30 @@ get_new_state(struct path *pp)
> >  	return newstate;
> >  }
> >  
> > -static void
> > -do_sync_mpp(struct vectors * vecs, struct multipath *mpp)
> > +/* Returns true if the mpp was deleted */
> > +static int
> > +do_sync_mpp(struct vectors *vecs, struct multipath *mpp)
> >  {
> > -	int i, ret;
> > -	struct path *pp;
> > +	int ret;
> > +
> > +	ret = refresh_multipath(vecs, mpp);
> > +	if (ret)
> > +		return ret;
> >  
> > -	ret = update_multipath_strings(mpp, vecs->pathvec);
> > -	if (ret != DMP_OK) {
> > -		condlog(1, "%s: %s", mpp->alias, ret == DMP_NOT_FOUND ?
> > -			"device not found" :
> > -			"couldn't synchronize with kernel state");
> > -		vector_foreach_slot (mpp->paths, pp, i)
> > -			pp->dmstate = PSTATE_UNDEF;
> > -		return;
> > -	}
> >  	set_no_path_retry(mpp);
> > +	return 0;
> >  }
> >  
> > -static void
> > +static int
> >  sync_mpp(struct vectors * vecs, struct multipath *mpp, unsigned int ticks)
> >  {
> >  	if (mpp->sync_tick)
> >  		mpp->sync_tick -= (mpp->sync_tick > ticks) ? ticks :
> >  				  mpp->sync_tick;
> >  	if (mpp->sync_tick)
> > -		return;
> > +		return 0;
> >  
> > -	do_sync_mpp(vecs, mpp);
> > +	return do_sync_mpp(vecs, mpp);
> >  }
> >  
> >  static int
> > @@ -2513,12 +2509,10 @@ update_path_state (struct vectors * vecs, struct path * pp)
> >  		return handle_path_wwid_change(pp, vecs)? CHECK_PATH_REMOVED :
> >  							  CHECK_PATH_SKIPPED;
> >  	}
> > -	if (pp->mpp->synced_count == 0) {
> > -		do_sync_mpp(vecs, pp->mpp);
> > +	if (pp->mpp->synced_count == 0 && do_sync_mpp(vecs, pp->mpp))
> >  		/* if update_multipath_strings orphaned the path, quit early */
> > -		if (!pp->mpp)
> > -			return CHECK_PATH_SKIPPED;
> > -	}
> > +		return CHECK_PATH_SKIPPED;
> > +
> >  	if ((newstate != PATH_UP && newstate != PATH_GHOST &&
> >  	     newstate != PATH_PENDING) && (pp->state == PATH_DELAYED)) {
> >  		/* If path state become failed again cancel path delay state */
> > @@ -3018,8 +3012,11 @@ checkerloop (void *ap)
> >  				mpp->synced_count = 0;
> >  			if (checker_state == CHECKER_STARTING) {
> >  				vector_foreach_slot(vecs->mpvec, mpp, i) {
> > -					sync_mpp(vecs, mpp, ticks);
> > -					mpp->prio_update = PRIO_UPDATE_NONE;
> > +					if (sync_mpp(vecs, mpp, ticks))
> > +						/* map deleted */
> > +						i--;
> > +					else
> > +						mpp->prio_update = PRIO_UPDATE_NONE;
> >  				}
> >  				vector_foreach_slot(vecs->pathvec, pp, i)
> >  					pp->is_checked = CHECK_PATH_UNCHECKED;
> > -- 
> > 2.47.0