firewire: core: do not use del_timer_sync() in interrupt context

Because we might be in interrupt context, replace del_timer_sync() with
del_timer().  If the timer is already running, we know that it will
clean up the transaction, so we do not need to do any further processing
in the normal transaction handler.

Many thanks to Yong Zhang for diagnosing this.

Reported-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
diff --git a/drivers/firewire/core-transaction.c b/drivers/firewire/core-transaction.c
index ca7ca56..b42a0bd 100644
--- a/drivers/firewire/core-transaction.c
+++ b/drivers/firewire/core-transaction.c
@@ -81,6 +81,10 @@
 	spin_lock_irqsave(&card->lock, flags);
 	list_for_each_entry(t, &card->transaction_list, link) {
 		if (t == transaction) {
+			if (!del_timer(&t->split_timeout_timer)) {
+				spin_unlock_irqrestore(&card->lock, flags);
+				goto timed_out;
+			}
 			list_del_init(&t->link);
 			card->tlabel_mask &= ~(1ULL << t->tlabel);
 			break;
@@ -89,11 +93,11 @@
 	spin_unlock_irqrestore(&card->lock, flags);
 
 	if (&t->link != &card->transaction_list) {
-		del_timer_sync(&t->split_timeout_timer);
 		t->callback(card, rcode, NULL, 0, t->callback_data);
 		return 0;
 	}
 
+ timed_out:
 	return -ENOENT;
 }
 
@@ -921,6 +925,10 @@
 	spin_lock_irqsave(&card->lock, flags);
 	list_for_each_entry(t, &card->transaction_list, link) {
 		if (t->node_id == source && t->tlabel == tlabel) {
+			if (!del_timer(&t->split_timeout_timer)) {
+				spin_unlock_irqrestore(&card->lock, flags);
+				goto timed_out;
+			}
 			list_del_init(&t->link);
 			card->tlabel_mask &= ~(1ULL << t->tlabel);
 			break;
@@ -929,6 +937,7 @@
 	spin_unlock_irqrestore(&card->lock, flags);
 
 	if (&t->link == &card->transaction_list) {
+ timed_out:
 		fw_notify("Unsolicited response (source %x, tlabel %x)\n",
 			  source, tlabel);
 		return;
@@ -963,8 +972,6 @@
 		break;
 	}
 
-	del_timer_sync(&t->split_timeout_timer);
-
 	/*
 	 * The response handler may be executed while the request handler
 	 * is still pending.  Cancel the request handler.