Merge branch 'Two fixes for cpu-map'

Hou Tao says:

====================

The patchset fixes two reported warning in cpu-map when running
xdp_redirect_cpu and some RT threads concurrently. Patch #1 fixes
the warning in __cpu_map_ring_cleanup() when kthread is stopped
prematurely. Patch #2 fixes the warning in __xdp_return() when
there are pending skbs in ptr_ring.

Please see individual patches for more details. And comments are always
welcome.

====================

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

Author: Martin KaFai Lau

kernel/bpf/cpumap.c

@@ -28,6 +28,7 @@
 #include <linux/sched.h>
 #include <linux/workqueue.h>
 #include <linux/kthread.h>
+#include <linux/completion.h>
 #include <trace/events/xdp.h>
 #include <linux/btf_ids.h>
 
@@ -73,6 +74,7 @@ struct bpf_cpu_map_entry {
 	struct rcu_head rcu;
 
 	struct work_struct kthread_stop_wq;
+	struct completion kthread_running;
 };
 
 struct bpf_cpu_map {
@@ -129,11 +131,17 @@ static void __cpu_map_ring_cleanup(struct ptr_ring *ring)
 	 * invoked cpu_map_kthread_stop(). Catch any broken behaviour
 	 * gracefully and warn once.
 	 */
-	struct xdp_frame *xdpf;
+	void *ptr;
 
-	while ((xdpf = ptr_ring_consume(ring)))
-		if (WARN_ON_ONCE(xdpf))
-			xdp_return_frame(xdpf);
+	while ((ptr = ptr_ring_consume(ring))) {
+		WARN_ON_ONCE(1);
+		if (unlikely(__ptr_test_bit(0, &ptr))) {
+			__ptr_clear_bit(0, &ptr);
+			kfree_skb(ptr);
+			continue;
+		}
+		xdp_return_frame(ptr);
+	}
 }
 
 static void put_cpu_map_entry(struct bpf_cpu_map_entry *rcpu)
@@ -153,7 +161,6 @@ static void put_cpu_map_entry(struct bpf_cpu_map_entry *rcpu)
 static void cpu_map_kthread_stop(struct work_struct *work)
 {
 	struct bpf_cpu_map_entry *rcpu;
-	int err;
 
 	rcpu = container_of(work, struct bpf_cpu_map_entry, kthread_stop_wq);
 
@@ -163,14 +170,7 @@ static void cpu_map_kthread_stop(struct work_struct *work)
 	rcu_barrier();
 
 	/* kthread_stop will wake_up_process and wait for it to complete */
-	err = kthread_stop(rcpu->kthread);
-	if (err) {
-		/* kthread_stop may be called before cpu_map_kthread_run
-		 * is executed, so we need to release the memory related
-		 * to rcpu.
-		 */
-		put_cpu_map_entry(rcpu);
-	}
+	kthread_stop(rcpu->kthread);
 }
 
 static void cpu_map_bpf_prog_run_skb(struct bpf_cpu_map_entry *rcpu,
@@ -298,11 +298,11 @@ static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
 	return nframes;
 }
 
-
 static int cpu_map_kthread_run(void *data)
 {
 	struct bpf_cpu_map_entry *rcpu = data;
 
+	complete(&rcpu->kthread_running);
 	set_current_state(TASK_INTERRUPTIBLE);
 
 	/* When kthread gives stop order, then rcpu have been disconnected
@@ -467,6 +467,7 @@ __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value,
 		goto free_ptr_ring;
 
 	/* Setup kthread */
+	init_completion(&rcpu->kthread_running);
 	rcpu->kthread = kthread_create_on_node(cpu_map_kthread_run, rcpu, numa,
 					       "cpumap/%d/map:%d", cpu,
 					       map->id);
@@ -480,6 +481,12 @@ __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value,
 	kthread_bind(rcpu->kthread, cpu);
 	wake_up_process(rcpu->kthread);
 
+	/* Make sure kthread has been running, so kthread_stop() will not
+	 * stop the kthread prematurely and all pending frames or skbs
+	 * will be handled by the kthread before kthread_stop() returns.
+	 */
+	wait_for_completion(&rcpu->kthread_running);
+
 	return rcpu;
 
 free_prog: