net-sysfs: remove possible sleep from an RCU read-side critical section

xps_queue_show is mostly made of an RCU read-side critical section and
calls bitmap_zalloc with GFP_KERNEL in the middle of it. That is not
allowed as this call may sleep and such behaviours aren't allowed in RCU
read-side critical sections. Fix this by using GFP_NOWAIT instead.

Fixes: 5478fcd ("net: embed nr_ids in the xps maps")
Reported-by: kernel test robot <oliver.sang@intel.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/net-sysfs.c

@@ -1378,7 +1378,7 @@ static ssize_t xps_queue_show(struct net_device *dev, unsigned int index,
 	nr_ids = dev_maps ? dev_maps->nr_ids :
 		 (type == XPS_CPUS ? nr_cpu_ids : dev->num_rx_queues);
 
-	mask = bitmap_zalloc(nr_ids, GFP_KERNEL);
+	mask = bitmap_zalloc(nr_ids, GFP_NOWAIT);
 	if (!mask) {
 		rcu_read_unlock();
 		return -ENOMEM;