Merge tag 'firewire-fixes-6.19-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/ieee1394/linux1394

Pull firewire fix from Takashi Sakamoto:
 "Fix a race condition introduced in v6.18.

  Andreas Persson discovered this issue while working with Focusrite
  Saffire Pro 40 (TCD33070). The fw_card instance maintains a linked
  list of pending transactions, which must be protected against
  concurrent access.

  However, a commit b5725cf ("firewire: core: use spin lock
  specific to timer for split transaction") unintentionally allowed
  concurrent accesses to this list.

  Fix this by adjusting the relevant critical sections to properly
  serialize access"

* tag 'firewire-fixes-6.19-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/ieee1394/linux1394:
  firewire: core: fix race condition against transaction list

Author: torvalds

drivers/firewire/core-transaction.c

@@ -173,20 +173,14 @@ static void split_transaction_timeout_callback(struct timer_list *timer)
 	}
 }
 
-static void start_split_transaction_timeout(struct fw_transaction *t,
-					    struct fw_card *card)
+// card->transactions.lock should be acquired in advance for the linked list.
+static void start_split_transaction_timeout(struct fw_transaction *t, unsigned int delta)
 {
-	unsigned long delta;
-
 	if (list_empty(&t->link) || WARN_ON(t->is_split_transaction))
 		return;
 
 	t->is_split_transaction = true;
 
-	// NOTE: This can be without irqsave when we can guarantee that __fw_send_request() for
-	// local destination never runs in any type of IRQ context.
-	scoped_guard(spinlock_irqsave, &card->split_timeout.lock)
-		delta = card->split_timeout.jiffies;
 	mod_timer(&t->split_timeout_timer, jiffies + delta);
 }
 
@@ -207,13 +201,20 @@ static void transmit_complete_callback(struct fw_packet *packet,
 		break;
 	case ACK_PENDING:
 	{
+		unsigned int delta;
+
 		// NOTE: This can be without irqsave when we can guarantee that __fw_send_request() for
 		// local destination never runs in any type of IRQ context.
 		scoped_guard(spinlock_irqsave, &card->split_timeout.lock) {
 			t->split_timeout_cycle =
 				compute_split_timeout_timestamp(card, packet->timestamp) & 0xffff;
+			delta = card->split_timeout.jiffies;
 		}
-		start_split_transaction_timeout(t, card);
+
+		// NOTE: This can be without irqsave when we can guarantee that __fw_send_request() for
+		// local destination never runs in any type of IRQ context.
+		scoped_guard(spinlock_irqsave, &card->transactions.lock)
+			start_split_transaction_timeout(t, delta);
 		break;
 	}
 	case ACK_BUSY_X: