[PATCHv2] block: Fix dev_t minor allocation lifetime

Keith Busch
2014-08-26T15:08:17Z

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>
---
v1->v2:

Applied comments from Willy: fixed gfp mask in idr_alloc to not wait,
and preload.

block/genhd.c | 24 ++++++++++++++----------
block/partition-generic.c | 2 +-
2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 791f419..09da5e4 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 789cdea..0d9e5f9 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);
}
--
1.7.10.4