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dm: fix add_disk() NULL pointer due to race with free_dev()

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Commit c4db59d31e ("fs: don't reassign dirty inodes to
default_backing_dev_info") exposed DM to a latent race in free_dev() vs
add_disk() in relation to management of the device's minor number.

Fix this by refactoring free_dev() to match cleanup order of the
alloc_dev() error path.  Move cleanup of the gendisk, queue, and bdev
to _before_ the cleanup of the idr managed minor number.

Also, purely due to cleanup that fell out during the free_dev() audit:
- adjust dm_blk_close() to access the gendisk's private_data under
  the _minor_lock spinlock.
- move __dm_destroy()'s dm_get_live_table() call out from under the
  _minor_lock spinlock.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1202449

Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
Reported-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Mike Snitzer 2015-03-23 17:01:43 -04:00
parent e5db29806b
commit 63a4f065ec
1 changed files with 16 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
drivers/md/dm.c
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@ -433,7 +433,6 @@ static int dm_blk_open(struct block_device *bdev, fmode_t mode)
dm_get(md);
atomic_inc(&md->open_count);
out:
spin_unlock(&_minor_lock);
@ -442,16 +441,20 @@ out:
static void dm_blk_close(struct gendisk *disk, fmode_t mode)
{
struct mapped_device *md = disk->private_data;
struct mapped_device *md;
spin_lock(&_minor_lock);
md = disk->private_data;
if (WARN_ON(!md))
goto out;
if (atomic_dec_and_test(&md->open_count) &&
(test_bit(DMF_DEFERRED_REMOVE, &md->flags)))
queue_work(deferred_remove_workqueue, &deferred_remove_work);
dm_put(md);
out:
spin_unlock(&_minor_lock);
}
@ -2241,7 +2244,6 @@ static void free_dev(struct mapped_device *md)
int minor = MINOR(disk_devt(md->disk));
unlock_fs(md);
bdput(md->bdev);
destroy_workqueue(md->wq);
if (md->kworker_task)
@ -2252,19 +2254,22 @@ static void free_dev(struct mapped_device *md)
mempool_destroy(md->rq_pool);
if (md->bs)
bioset_free(md->bs);
blk_integrity_unregister(md->disk);
del_gendisk(md->disk);
cleanup_srcu_struct(&md->io_barrier);
free_table_devices(&md->table_devices);
free_minor(minor);
dm_stats_cleanup(&md->stats);
spin_lock(&_minor_lock);
md->disk->private_data = NULL;
spin_unlock(&_minor_lock);
if (blk_get_integrity(md->disk))
blk_integrity_unregister(md->disk);
del_gendisk(md->disk);
put_disk(md->disk);
blk_cleanup_queue(md->queue);
dm_stats_cleanup(&md->stats);
bdput(md->bdev);
free_minor(minor);
module_put(THIS_MODULE);
kfree(md);
}
@ -2642,8 +2647,9 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
might_sleep();
spin_lock(&_minor_lock);
map = dm_get_live_table(md, &srcu_idx);
spin_lock(&_minor_lock);
idr_replace(&_minor_idr, MINOR_ALLOCED, MINOR(disk_devt(dm_disk(md))));
set_bit(DMF_FREEING, &md->flags);
spin_unlock(&_minor_lock);