We tripped on a WRONG():
-- panic.show --
Last panic at: Sun, 31 Jul 2016 01:43:54 GMT
"Wrong turn at vdir.c:209:
thread = (cache-worker)
version = varnish-4.1.3 revision 5e3b6d2
It looks like that while in vdir_pick_by_weight, somebody in vdir_pick_be changes vd->vbm under us.
Not panicking would be nice
Switching vdir_pick_be lock acquisition to vdir_wrlock instead of vdir_rdlock.
EL6, varnish 4.1.3
As discussed in IRC, I will look into this.
Revert to wrlock to avoid vd->vbm trampling
Backport review: Fix backported as c3374b1