dm mpath: detect invalid map_context

The map_context pointer should always be set. However, we have reports
that upon requeuing it is not set correctly.  So add set and clear
functions with a BUG_ON() to track the issue properly.

Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Acked-by: Hannes Reinecke <hare@suse.de>
Tested-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Dave Wysochanski <dwysocha@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 32 insertions, 14 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 801d92d237cf..e92a0005eeff 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -226,6 +226,27 @@ static void free_multipath(struct multipath *m)
         kfree(m);
 }
 
+static int set_mapinfo(struct multipath *m, union map_info *info)
+{
+        struct dm_mpath_io *mpio;
+
+        mpio = mempool_alloc(m->mpio_pool, GFP_ATOMIC);
+        if (!mpio)
+                return -ENOMEM;
+
+        memset(mpio, 0, sizeof(*mpio));
+        info->ptr = mpio;
+
+        return 0;
+}
+
+static void clear_mapinfo(struct multipath *m, union map_info *info)
+{
+        struct dm_mpath_io *mpio = info->ptr;
+
+        info->ptr = NULL;
+        mempool_free(mpio, m->mpio_pool);
+}
 
 /*-----------------------------------------------
  * Path selection
@@ -341,13 +362,14 @@ static int __must_push_back(struct multipath *m)
 }
 
 static int map_io(struct multipath *m, struct request *clone,
-                  struct dm_mpath_io *mpio, unsigned was_queued)
+                  union map_info *map_context, unsigned was_queued)
 {
         int r = DM_MAPIO_REMAPPED;
         size_t nr_bytes = blk_rq_bytes(clone);
         unsigned long flags;
         struct pgpath *pgpath;
         struct block_device *bdev;
+        struct dm_mpath_io *mpio = map_context->ptr;
 
         spin_lock_irqsave(&m->lock, flags);
 
@@ -423,7 +445,6 @@ static void dispatch_queued_ios(struct multipath *m)
 {
         int r;
         unsigned long flags;
-        struct dm_mpath_io *mpio;
         union map_info *info;
         struct request *clone, *n;
         LIST_HEAD(cl);
@@ -436,16 +457,15 @@ static void dispatch_queued_ios(struct multipath *m)
                 list_del_init(&clone->queuelist);
 
                 info = dm_get_rq_mapinfo(clone);
-                mpio = info->ptr;
 
-                r = map_io(m, clone, mpio, 1);
+                r = map_io(m, clone, info, 1);
                 if (r < 0) {
-                        mempool_free(mpio, m->mpio_pool);
+                        clear_mapinfo(m, info);
                         dm_kill_unmapped_request(clone, r);
                 } else if (r == DM_MAPIO_REMAPPED)
                         dm_dispatch_request(clone);
                 else if (r == DM_MAPIO_REQUEUE) {
-                        mempool_free(mpio, m->mpio_pool);
+                        clear_mapinfo(m, info);
                         dm_requeue_unmapped_request(clone);
                 }
         }
@@ -908,20 +928,16 @@ static int multipath_map(struct dm_target *ti, struct request *clone,
                          union map_info *map_context)
 {
         int r;
-        struct dm_mpath_io *mpio;
         struct multipath *m = (struct multipath *) ti->private;
 
-        mpio = mempool_alloc(m->mpio_pool, GFP_ATOMIC);
-        if (!mpio)
+        if (set_mapinfo(m, map_context) < 0)
                 /* ENOMEM, requeue */
                 return DM_MAPIO_REQUEUE;
-        memset(mpio, 0, sizeof(*mpio));
 
-        map_context->ptr = mpio;
         clone->cmd_flags |= REQ_FAILFAST_TRANSPORT;
-        r = map_io(m, clone, mpio, 0);
+        r = map_io(m, clone, map_context, 0);
         if (r < 0 || r == DM_MAPIO_REQUEUE)
-                mempool_free(mpio, m->mpio_pool);
+                clear_mapinfo(m, map_context);
 
         return r;
 }
@@ -1261,13 +1277,15 @@ static int multipath_end_io(struct dm_target *ti, struct request *clone,
         struct path_selector *ps;
         int r;
 
+        BUG_ON(!mpio);
+
         r  = do_end_io(m, clone, error, mpio);
         if (pgpath) {
                 ps = &pgpath->pg->ps;
                 if (ps->type->end_io)
                         ps->type->end_io(ps, &pgpath->path, mpio->nr_bytes);
         }
-        mempool_free(mpio, m->mpio_pool);
+        clear_mapinfo(m, map_context);
 
         return r;
 }