drbd: device->ldev is not guaranteed on an D_ATTACHING disk

Some parts of the code assumed that get_ldev_if_state(device, D_ATTACHING)
is sufficient to access the ldev member of the device object. That was
wrong. ldev may not be there or might be freed at any time if the device
has a disk state of D_ATTACHING.

bm_rw()
  Documented that drbd_bm_read() is only called from drbd_adm_attach.
  drbd_bm_write() is only called when a reference is held, and it is
  documented that a caller has to hold a reference before calling
  drbd_bm_write()

drbd_bm_write_page()
  Use get_ldev() instead of get_ldev_if_state(device, D_ATTACHING)

drbd_bmio_set_n_write()
  No longer use get_ldev_if_state(device, D_ATTACHING). All callers
  hold a reference to ldev now.

drbd_bmio_clear_n_write()
  All callers where holding a reference of ldev anyways. Remove the
  misleading get_ldev_if_state(device, D_ATTACHING)

drbd_reconsider_max_bio_size()
  Removed the get_ldev_if_state(device, D_ATTACHING). All callers
  now pass a struct drbd_backing_dev* when they have a proper
  reference, or a NULL pointer.
  Before this fix, the receiver could trigger a NULL pointer
  deref when in drbd_reconsider_max_bio_size()

drbd_bump_write_ordering()
  Used get_ldev_if_state(device, D_ATTACHING) with the wrong assumption.
  Remove it, and allow the caller to pass in a struct drbd_backing_dev*
  when the caller knows that accessing this bdev is safe.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c
index 1aa29f8fdfe1..ed310415020b 100644
--- a/drivers/block/drbd/drbd_bitmap.c
+++ b/drivers/block/drbd/drbd_bitmap.c
@@ -1085,6 +1085,8 @@ static int bm_rw(struct drbd_device *device, int rw, unsigned flags, unsigned la
 		kfree(ctx);
 		return -ENODEV;
 	}
+	/* Here D_ATTACHING is sufficient since drbd_bm_read() is called only from
+	   drbd_adm_attach(), after device->ldev was assigned. */
 
 	if (!ctx->flags)
 		WARN_ON(!(BM_LOCKED_MASK & b->bm_flags));
@@ -1260,7 +1262,7 @@ int drbd_bm_write_page(struct drbd_device *device, unsigned int idx) __must_hold
 		.kref = { ATOMIC_INIT(2) },
 	};
 
-	if (!get_ldev_if_state(device, D_ATTACHING)) {  /* put is in bm_aio_ctx_destroy() */
+	if (!get_ldev(device)) {  /* put is in bm_aio_ctx_destroy() */
 		drbd_err(device, "ASSERT FAILED: get_ldev_if_state() == 1 in drbd_bm_write_page()\n");
 		kfree(ctx);
 		return -ENODEV;