2 files changed, 20 insertions, 4 deletions

diff --git a/block/genhd.c b/block/genhd.c
index 2f7feda61e35..d84a7df1e2a0 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -181,6 +181,12 @@ void disk_part_iter_exit(struct disk_part_iter *piter)
 }
 EXPORT_SYMBOL_GPL(disk_part_iter_exit);
 
+static inline int sector_in_part(struct hd_struct *part, sector_t sector)
+{
+        return part->start_sect <= sector &&
+                sector < part->start_sect + part->nr_sects;
+}
+
 /**
  * disk_map_sector_rcu - map sector to partition
  * @disk: gendisk of interest
@@ -199,16 +205,22 @@ EXPORT_SYMBOL_GPL(disk_part_iter_exit);
 struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
 {
         struct disk_part_tbl *ptbl;
+        struct hd_struct *part;
         int i;
 
         ptbl = rcu_dereference(disk->part_tbl);
 
+        part = rcu_dereference(ptbl->last_lookup);
+        if (part && sector_in_part(part, sector))
+                return part;
+
         for (i = 1; i < ptbl->len; i++) {
-                struct hd_struct *part = rcu_dereference(ptbl->part[i]);
+                part = rcu_dereference(ptbl->part[i]);
 
-                if (part && part->start_sect <= sector &&
-                    sector < part->start_sect + part->nr_sects)
+                if (part && sector_in_part(part, sector)) {
+                        rcu_assign_pointer(ptbl->last_lookup, part);
                         return part;
+                }
         }
         return &disk->part0;
 }
@@ -888,8 +900,11 @@ static void disk_replace_part_tbl(struct gendisk *disk,
         struct disk_part_tbl *old_ptbl = disk->part_tbl;
 
         rcu_assign_pointer(disk->part_tbl, new_ptbl);
-        if (old_ptbl)
+
+        if (old_ptbl) {
+                rcu_assign_pointer(old_ptbl->last_lookup, NULL);
                 call_rcu(&old_ptbl->rcu_head, disk_free_ptbl_rcu_cb);
+        }
 }
 
 /**
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 3df7742ce246..16948eaecae3 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -126,6 +126,7 @@ struct blk_scsi_cmd_filter {
 struct disk_part_tbl {
         struct rcu_head rcu_head;
         int len;
+        struct hd_struct *last_lookup;
         struct hd_struct *part[];
 };