iavf: fix potential deadlock on allocation failure

In iavf_adminq_task(), if kzalloc() fails to allocate the event.msg_buf,
the function will exit without releasing the adapter->crit_lock.

This is unlikely, but if it happens, the next access to that mutex will
deadlock.

Fix this by moving the unlock to the end of the function, and adding a new
label to allow jumping to the unlock portion of the function exit flow.

Fixes: fc2e6b3 ("iavf: Rework mutexes for better synchronisation")
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/iavf/iavf_main.c

@@ -3264,7 +3264,7 @@ static void iavf_adminq_task(struct work_struct *work)
 	event.buf_len = IAVF_MAX_AQ_BUF_SIZE;
 	event.msg_buf = kzalloc(event.buf_len, GFP_KERNEL);
 	if (!event.msg_buf)
-		goto out;
+		goto unlock;
 
 	do {
 		ret = iavf_clean_arq_element(hw, &event, &pending);
@@ -3279,7 +3279,6 @@ static void iavf_adminq_task(struct work_struct *work)
 		if (pending != 0)
 			memset(event.msg_buf, 0, IAVF_MAX_AQ_BUF_SIZE);
 	} while (pending);
-	mutex_unlock(&adapter->crit_lock);
 
 	if (iavf_is_reset_in_progress(adapter))
 		goto freedom;
@@ -3323,6 +3322,8 @@ static void iavf_adminq_task(struct work_struct *work)
 
 freedom:
 	kfree(event.msg_buf);
+unlock:
+	mutex_unlock(&adapter->crit_lock);
 out:
 	/* re-enable Admin queue interrupt cause */
 	iavf_misc_irq_enable(adapter);