[dm-devel] [PATCH 4/5] multipathd: reload map if the path groups are out of order

[Martin Wilck]

On Wed, 2023-05-24 at 18:21 -0500, Benjamin Marzinski wrote:
> need_switch_pathgroup() only checks if the currently used pathgroup
> is
> not the highest priority pathgroup. If it isn't, all multipathd does
> is
> instruct the kernel to switch to the correct pathgroup.  However, the
> kernel treats the pathgroups as if they were ordered by priority.
> When
> the kernel runs out of paths to use in the currently selected
> pathgroup,
> it will start checking the pathgroups in order until it finds one
> with
> usable paths.
> 
> need_switch_pathgroup() should also check if the pathgroups are out
> of
> order, and if so, multipathd should reload the map to reorder them
> correctly.
> 
> Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
> ---
>  libmultipath/libmultipath.version |  5 ++++
>  libmultipath/switchgroup.c        | 27 ++++++++++++++++++++++
>  libmultipath/switchgroup.h        |  1 +
>  multipathd/main.c                 | 38 +++++++++++++++++++++--------
> --
>  4 files changed, 59 insertions(+), 12 deletions(-)
> 
> diff --git a/libmultipath/libmultipath.version
> b/libmultipath/libmultipath.version
> index 8f72c452..38074699 100644
> --- a/libmultipath/libmultipath.version
> +++ b/libmultipath/libmultipath.version
> @@ -237,3 +237,8 @@ global:
>  local:
>         *;
>  };
> +
> +LIBMULTIPATH_19.1.0 {
> +global:
> +       path_groups_in_order;
> +} LIBMULTIPATH_19.0.0;
> diff --git a/libmultipath/switchgroup.c b/libmultipath/switchgroup.c
> index b1e1f39b..b1180839 100644
> --- a/libmultipath/switchgroup.c
> +++ b/libmultipath/switchgroup.c
> @@ -7,6 +7,33 @@
>  #include "structs.h"
>  #include "switchgroup.h"
>  
> +bool path_groups_in_order(struct multipath *mpp)
> +{
> +       int i;
> +       struct pathgroup *pgp;
> +       bool seen_marginal_pg = false;
> +       int last_prio = INT_MAX;
> +
> +       if (VECTOR_SIZE(mpp->pg) < 2)
> +               return true;
> +
> +       vector_foreach_slot(mpp->pg, pgp, i) {
> +               /* skip pgs with PRIO_UNDEF, since this is likely
> temporary */
> +               if (!pgp->paths || pgp->priority == PRIO_UNDEF)
> +                       continue;
> +               if (pgp->marginal && !seen_marginal_pg) {
> +                       last_prio = INT_MAX;
> +                       continue;
> +               }
> +               if (seen_marginal_pg && !pgp->marginal)
> +                       return false;
> +               if (pgp->priority > last_prio)
> +                       return false;
> +               last_prio = pgp->priority;
> +       }
> +       return true;
> +}
> +
>  void path_group_prio_update(struct pathgroup *pgp)
>  {
>         int i;
> diff --git a/libmultipath/switchgroup.h b/libmultipath/switchgroup.h
> index 9365e2e2..43dbb6c9 100644
> --- a/libmultipath/switchgroup.h
> +++ b/libmultipath/switchgroup.h
> @@ -1,2 +1,3 @@
>  void path_group_prio_update (struct pathgroup * pgp);
>  int select_path_group (struct multipath * mpp);
> +bool path_groups_in_order(struct multipath *mpp);
> diff --git a/multipathd/main.c b/multipathd/main.c
> index e7c272ad..2ea7c76b 100644
> --- a/multipathd/main.c
> +++ b/multipathd/main.c
> @@ -396,7 +396,7 @@ void put_multipath_config(__attribute__((unused))
> void *arg)
>  }
>  
>  static int
> -need_switch_pathgroup (struct multipath * mpp, int refresh)
> +need_switch_pathgroup (struct multipath * mpp, int refresh, bool
> *need_reload)
>  {
>         struct pathgroup * pgp;
>         struct path * pp;
> @@ -404,6 +404,7 @@ need_switch_pathgroup (struct multipath * mpp,
> int refresh)
>         struct config *conf;
>         int bestpg;
>  
> +       *need_reload = false;
>         if (!mpp)
>                 return 0;
>  
> @@ -430,10 +431,9 @@ need_switch_pathgroup (struct multipath * mpp,
> int refresh)
>                 return 0;
>  
>         mpp->bestpg = bestpg;
> -       if (mpp->bestpg != mpp->nextpg)
> -               return 1;
> +       *need_reload = !path_groups_in_order(mpp);

This will start another loop over the path groups. Can we just
integrate the path_groups_in_order() logic into the loop right here?



>  
> -       return 0;
> +       return (*need_reload || mpp->bestpg != mpp->nextpg);
>  }
>  
>  static void
> @@ -1982,20 +1982,26 @@ ghost_delay_tick(struct vectors *vecs)
>  }
>  
>  static void
> -deferred_failback_tick (vector mpvec)
> +deferred_failback_tick (struct vectors *vecs)
>  {
>         struct multipath * mpp;
>         unsigned int i;
> +       bool need_reload;
>  
> -       vector_foreach_slot (mpvec, mpp, i) {
> +       vector_foreach_slot (vecs->mpvec, mpp, i) {
>                 /*
>                  * deferred failback getting sooner
>                  */
>                 if (mpp->pgfailback > 0 && mpp->failback_tick > 0) {
>                         mpp->failback_tick--;
>  
> -                       if (!mpp->failback_tick &&
> need_switch_pathgroup(mpp, 1))
> -                               switch_pathgroup(mpp);
> +                       if (!mpp->failback_tick &&
> +                           need_switch_pathgroup(mpp, 1,
> &need_reload)) {
> +                               if (need_reload)
> +                                       reload_and_sync_map(mpp,
> vecs, 0);
> +                               else
> +                                       switch_pathgroup(mpp);
> +                       }
>                 }
>         }
>  }
> @@ -2579,6 +2585,7 @@ check_path (struct vectors * vecs, struct path
> * pp, unsigned int ticks)
>                 int prio_changed = update_prio(pp, new_path_up);
>                 bool need_refresh = (!new_path_up && prio_changed &&
>                                      pp->priority != PRIO_UNDEF);
> +               bool need_reload;
>  
>                 if (prio_changed &&
>                     pp->mpp->pgpolicyfn == (pgpolicyfn
> *)group_by_prio &&
> @@ -2586,15 +2593,22 @@ check_path (struct vectors * vecs, struct
> path * pp, unsigned int ticks)
>                         condlog(2, "%s: path priorities changed.
> reloading",
>                                 pp->mpp->alias);
>                         reload_and_sync_map(pp->mpp, vecs,
> !new_path_up);
> -               } else if (need_switch_pathgroup(pp->mpp,
> need_refresh)) {
> +               } else if (need_switch_pathgroup(pp->mpp,
> need_refresh,
> +                                                &need_reload)) {
>                         if (pp->mpp->pgfailback > 0 &&
>                             (new_path_up || pp->mpp->failback_tick <=
> 0))
>                                 pp->mpp->failback_tick =
>                                         pp->mpp->pgfailback + 1;
>                         else if (pp->mpp->pgfailback == -
> FAILBACK_IMMEDIATE ||
>                                  (chkr_new_path_up &&
> -                                 followover_should_failback(pp)))
> -                               switch_pathgroup(pp->mpp);
> +                                 followover_should_failback(pp))) {
> +                               if (need_reload)
> +                                       reload_and_sync_map(pp->mpp,
> vecs,
> +                                                          
> !need_refresh &&
> +                                                          
> !new_path_up);
> +                               else
> +                                       switch_pathgroup(pp->mpp);
> +                       }
>                 }
>         }
>         return 1;
> @@ -2720,7 +2734,7 @@ unlock:
>                 pthread_cleanup_push(cleanup_lock, &vecs->lock);
>                 lock(&vecs->lock);
>                 pthread_testcancel();
> -               deferred_failback_tick(vecs->mpvec);
> +               deferred_failback_tick(vecs);
>                 retry_count_tick(vecs->mpvec);
>                 missing_uev_wait_tick(vecs);
>                 ghost_delay_tick(vecs);