block: Fix dev_t minor allocation lifetime

Releases the dev_t minor when all references are closed to prevent
another device from acquiring the same major/minor.

Since the partition's release may be invoked from call_rcu's soft-irq
context, the ext_dev_idr's mutex had to be replaced with a spinlock so
as not so sleep.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>

2 files changed, 15 insertions, 11 deletions

diff --git a/block/genhd.c b/block/genhd.c
index 791f41943132..09da5e4a8e03 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -28,10 +28,10 @@ struct kobject *block_depr;
 /* for extended dynamic devt allocation, currently only one major is used */
 #define NR_EXT_DEVT             (1 << MINORBITS)
 
-/* For extended devt allocation.  ext_devt_mutex prevents look up
+/* For extended devt allocation.  ext_devt_lock prevents look up
  * results from going away underneath its user.
  */
-static DEFINE_MUTEX(ext_devt_mutex);
+static DEFINE_SPINLOCK(ext_devt_lock);
 static DEFINE_IDR(ext_devt_idr);
 
 static struct device_type disk_type;
@@ -420,9 +420,13 @@ int blk_alloc_devt(struct hd_struct *part, dev_t *devt)
         }
 
         /* allocate ext devt */
-        mutex_lock(&ext_devt_mutex);
-        idx = idr_alloc(&ext_devt_idr, part, 0, NR_EXT_DEVT, GFP_KERNEL);
-        mutex_unlock(&ext_devt_mutex);
+        idr_preload(GFP_KERNEL);
+
+        spin_lock(&ext_devt_lock);
+        idx = idr_alloc(&ext_devt_idr, part, 0, NR_EXT_DEVT, GFP_NOWAIT);
+        spin_unlock(&ext_devt_lock);
+
+        idr_preload_end();
         if (idx < 0)
                 return idx == -ENOSPC ? -EBUSY : idx;
 
@@ -447,9 +451,9 @@ void blk_free_devt(dev_t devt)
                 return;
 
         if (MAJOR(devt) == BLOCK_EXT_MAJOR) {
-                mutex_lock(&ext_devt_mutex);
+                spin_lock(&ext_devt_lock);
                 idr_remove(&ext_devt_idr, blk_mangle_minor(MINOR(devt)));
-                mutex_unlock(&ext_devt_mutex);
+                spin_unlock(&ext_devt_lock);
         }
 }
 
@@ -665,7 +669,6 @@ void del_gendisk(struct gendisk *disk)
                 sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk)));
         pm_runtime_set_memalloc_noio(disk_to_dev(disk), false);
         device_del(disk_to_dev(disk));
-        blk_free_devt(disk_to_dev(disk)->devt);
 }
 EXPORT_SYMBOL(del_gendisk);
 
@@ -690,13 +693,13 @@ struct gendisk *get_gendisk(dev_t devt, int *partno)
         } else {
                 struct hd_struct *part;
 
-                mutex_lock(&ext_devt_mutex);
+                spin_lock(&ext_devt_lock);
                 part = idr_find(&ext_devt_idr, blk_mangle_minor(MINOR(devt)));
                 if (part && get_disk(part_to_disk(part))) {
                         *partno = part->partno;
                         disk = part_to_disk(part);
                 }
-                mutex_unlock(&ext_devt_mutex);
+                spin_unlock(&ext_devt_lock);
         }
 
         return disk;
@@ -1098,6 +1101,7 @@ static void disk_release(struct device *dev)
 {
         struct gendisk *disk = dev_to_disk(dev);
 
+        blk_free_devt(dev->devt);
         disk_release_events(disk);
         kfree(disk->random);
         disk_replace_part_tbl(disk, NULL);
diff --git a/block/partition-generic.c b/block/partition-generic.c
index 789cdea05893..0d9e5f97f0a8 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -211,6 +211,7 @@ static const struct attribute_group *part_attr_groups[] = {
 static void part_release(struct device *dev)
 {
         struct hd_struct *p = dev_to_part(dev);
+        blk_free_devt(dev->devt);
         free_part_stats(p);
         free_part_info(p);
         kfree(p);
@@ -253,7 +254,6 @@ void delete_partition(struct gendisk *disk, int partno)
         rcu_assign_pointer(ptbl->last_lookup, NULL);
         kobject_put(part->holder_dir);
         device_del(part_to_dev(part));
-        blk_free_devt(part_devt(part));
 
         hd_struct_put(part);
 }