firewire: sbp2: fix memory leak in sbp2_cancel_orbs or at send error

When an ORB was canceled (Command ORB i.e. SCSI request timed out, or
Management ORB timed out), or there was a send error in the initial
transaction, we missed to drop one of the ORB's references and thus
leaked memory.

Background:
In total, we hold 3 references to each Operation Request Block:
  - 1 during sbp2_scsi_queuecommand() or sbp2_send_management_orb()
    respectively,
  - 1 for the duration of the write transaction to the ORB_Pointer or
    Management_Agent register of the target,
  - 1 for as long as the ORB stays within the lu->orb_list, until
    the ORB is unlinked from the list and the orb->callback was
    executed.

The latter one of these 3 references is finished
  - normally by sbp2_status_write() when the target wrote status
    for a pending ORB,
  - or by sbp2_cancel_orbs() in case of an ORB time-out,
  - or by complete_transaction() in case of a send error.
Of them, the latter two lacked the kref_put.

Add the missing kref_put()s.  Add comments to the gets and puts of
references for transaction callbacks and ORB callbacks so that it is
easier to see what is supposed to happen.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

1 files changed, 7 insertions, 5 deletions

diff --git a/drivers/firewire/sbp2.c b/drivers/firewire/sbp2.c
index 9f76171717e5..e6cbe491f7ee 100644
--- a/drivers/firewire/sbp2.c
+++ b/drivers/firewire/sbp2.c
@@ -450,7 +450,7 @@ static void sbp2_status_write(struct fw_card *card, struct fw_request *request,
 
         if (&orb->link != &lu->orb_list) {
                 orb->callback(orb, &status);
-                kref_put(&orb->kref, free_orb);
+                kref_put(&orb->kref, free_orb); /* orb callback reference */
         } else {
                 fw_error("status write for unknown orb\n");
         }
@@ -480,12 +480,14 @@ static void complete_transaction(struct fw_card *card, int rcode,
         if (orb->rcode != RCODE_COMPLETE) {
                 list_del(&orb->link);
                 spin_unlock_irqrestore(&card->lock, flags);
+
                 orb->callback(orb, NULL);
+                kref_put(&orb->kref, free_orb); /* orb callback reference */
         } else {
                 spin_unlock_irqrestore(&card->lock, flags);
         }
 
-        kref_put(&orb->kref, free_orb);
+        kref_put(&orb->kref, free_orb); /* transaction callback reference */
 }
 
 static void sbp2_send_orb(struct sbp2_orb *orb, struct sbp2_logical_unit *lu,
@@ -501,9 +503,8 @@ static void sbp2_send_orb(struct sbp2_orb *orb, struct sbp2_logical_unit *lu,
         list_add_tail(&orb->link, &lu->orb_list);
         spin_unlock_irqrestore(&device->card->lock, flags);
 
-        /* Take a ref for the orb list and for the transaction callback. */
-        kref_get(&orb->kref);
-        kref_get(&orb->kref);
+        kref_get(&orb->kref); /* transaction callback reference */
+        kref_get(&orb->kref); /* orb callback reference */
 
         fw_send_request(device->card, &orb->t, TCODE_WRITE_BLOCK_REQUEST,
                         node_id, generation, device->max_speed, offset,
@@ -530,6 +531,7 @@ static int sbp2_cancel_orbs(struct sbp2_logical_unit *lu)
 
                 orb->rcode = RCODE_CANCELLED;
                 orb->callback(orb, NULL);
+                kref_put(&orb->kref, free_orb); /* orb callback reference */
         }
 
         return retval;