loop: fix LO_FLAGS_PARTSCAN hang

commit e02898b423802b1f3a3aaa7f16e896da069ba8f7 upstream.

loop_reread_partitions() needs to do I/O, but we just froze the queue,
so we end up waiting forever. This can easily be reproduced with losetup
-P. Fix it by moving the reread to after we unfreeze the queue.

Fixes: ecdd09597a57 ("block/loop: fix race between I/O and set_status")
Reported-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 8 insertions, 7 deletions

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index ccc3acc0c5ba..24d6cefceb32 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1142,13 +1142,6 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
              (info->lo_flags & LO_FLAGS_AUTOCLEAR))
                 lo->lo_flags ^= LO_FLAGS_AUTOCLEAR;
 
-        if ((info->lo_flags & LO_FLAGS_PARTSCAN) &&
-             !(lo->lo_flags & LO_FLAGS_PARTSCAN)) {
-                lo->lo_flags |= LO_FLAGS_PARTSCAN;
-                lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
-                loop_reread_partitions(lo, lo->lo_device);
-        }
-
         lo->lo_encrypt_key_size = info->lo_encrypt_key_size;
         lo->lo_init[0] = info->lo_init[0];
         lo->lo_init[1] = info->lo_init[1];
@@ -1163,6 +1156,14 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 
  exit:
         blk_mq_unfreeze_queue(lo->lo_queue);
+
+        if (!err && (info->lo_flags & LO_FLAGS_PARTSCAN) &&
+             !(lo->lo_flags & LO_FLAGS_PARTSCAN)) {
+                lo->lo_flags |= LO_FLAGS_PARTSCAN;
+                lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
+                loop_reread_partitions(lo, lo->lo_device);
+        }
+
         return err;
 }