net: sched: don't use GFP_KERNEL under spin lock

The new TC IDR code uses GFP_KERNEL under spin lock.  Which leads
to:

[  582.621091] BUG: sleeping function called from invalid context at ../mm/slab.h:416
[  582.629721] in_atomic(): 1, irqs_disabled(): 0, pid: 3379, name: tc
[  582.636939] 2 locks held by tc/3379:
[  582.641049]  #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff910354ce>] rtnetlink_rcv_msg+0x92e/0x1400
[  582.650958]  #1:  (&(&tn->idrinfo->lock)->rlock){+.-.+.}, at: [<ffffffff9110a5e0>] tcf_idr_create+0x2f0/0x8e0
[  582.662217] Preemption disabled at:
[  582.662222] [<ffffffff9110a5e0>] tcf_idr_create+0x2f0/0x8e0
[  582.672592] CPU: 9 PID: 3379 Comm: tc Tainted: G        W       4.13.0-rc7-debug-00648-g43503a79b9f0 #287
[  582.683432] Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.3.4 11/08/2016
[  582.691937] Call Trace:
...
[  582.742460]  kmem_cache_alloc+0x286/0x540
[  582.747055]  radix_tree_node_alloc.constprop.6+0x4a/0x450
[  582.753209]  idr_get_free_cmn+0x627/0xf80
...
[  582.815525]  idr_alloc_cmn+0x1a8/0x270
...
[  582.833804]  tcf_idr_create+0x31b/0x8e0
...

Try to preallocate the memory with idr_prealloc(GFP_KERNEL)
(as suggested by Eric Dumazet), and change the allocation
flags under spin lock.

Fixes: 65a206c01e8e ("net/sched: Change act_api and act_xxx modules to use IDR")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_api.c

@@ -296,10 +296,12 @@ err2:
 	spin_lock_init(&p->tcfa_lock);
 	/* user doesn't specify an index */
 	if (!index) {
+		idr_preload(GFP_KERNEL);
 		spin_lock_bh(&idrinfo->lock);
 		err = idr_alloc_ext(idr, NULL, &idr_index, 1, 0,
-				    GFP_KERNEL);
+				    GFP_ATOMIC);
 		spin_unlock_bh(&idrinfo->lock);
+		idr_preload_end();
 		if (err) {
 err3:
 			free_percpu(p->cpu_qstats);
@@ -307,10 +309,12 @@ err3:
 		}
 		p->tcfa_index = idr_index;
 	} else {
+		idr_preload(GFP_KERNEL);
 		spin_lock_bh(&idrinfo->lock);
 		err = idr_alloc_ext(idr, NULL, NULL, index, index + 1,
-				    GFP_KERNEL);
+				    GFP_ATOMIC);
 		spin_unlock_bh(&idrinfo->lock);
+		idr_preload_end();
 		if (err)
 			goto err3;
 		p->tcfa_index = index;