Merge branch 'bpf-lockdep-fixes'

Alexei Starovoitov says:

====================
v1->v2:
- reworded 2nd patch. It's a real dead lock. Not a false positive
- dropped the lockdep fix for up_read_non_owner in bpf_get_stackid

In addition to preempt_disable patch for socket filters
https://patchwork.ozlabs.org/patch/1032437/
First patch fixes lockdep false positive in percpu_freelist
Second patch fixes potential deadlock in bpf_prog_register
Third patch fixes another potential deadlock in stackmap access
from tracing bpf prog and from syscall.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/hashtab.c

@@ -686,7 +686,7 @@ static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
 	}
 
 	if (htab_is_prealloc(htab)) {
-		pcpu_freelist_push(&htab->freelist, &l->fnode);
+		__pcpu_freelist_push(&htab->freelist, &l->fnode);
 	} else {
 		atomic_dec(&htab->count);
 		l->htab = htab;
@@ -748,7 +748,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 		} else {
 			struct pcpu_freelist_node *l;
 
-			l = pcpu_freelist_pop(&htab->freelist);
+			l = __pcpu_freelist_pop(&htab->freelist);
 			if (!l)
 				return ERR_PTR(-E2BIG);
 			l_new = container_of(l, struct htab_elem, fnode);

kernel/bpf/percpu_freelist.c

@@ -28,8 +28,8 @@ void pcpu_freelist_destroy(struct pcpu_freelist *s)
 	free_percpu(s->freelist);
 }
 
-static inline void __pcpu_freelist_push(struct pcpu_freelist_head *head,
-					struct pcpu_freelist_node *node)
+static inline void ___pcpu_freelist_push(struct pcpu_freelist_head *head,
+					 struct pcpu_freelist_node *node)
 {
 	raw_spin_lock(&head->lock);
 	node->next = head->first;
@@ -37,12 +37,22 @@ static inline void __pcpu_freelist_push(struct pcpu_freelist_head *head,
 	raw_spin_unlock(&head->lock);
 }
 
-void pcpu_freelist_push(struct pcpu_freelist *s,
+void __pcpu_freelist_push(struct pcpu_freelist *s,
 			struct pcpu_freelist_node *node)
 {
 	struct pcpu_freelist_head *head = this_cpu_ptr(s->freelist);
 
-	__pcpu_freelist_push(head, node);
+	___pcpu_freelist_push(head, node);
+}
+
+void pcpu_freelist_push(struct pcpu_freelist *s,
+			struct pcpu_freelist_node *node)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	__pcpu_freelist_push(s, node);
+	local_irq_restore(flags);
 }
 
 void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
@@ -63,7 +73,7 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
 	for_each_possible_cpu(cpu) {
 again:
 		head = per_cpu_ptr(s->freelist, cpu);
-		__pcpu_freelist_push(head, buf);
+		___pcpu_freelist_push(head, buf);
 		i++;
 		buf += elem_size;
 		if (i == nr_elems)
@@ -74,14 +84,12 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
 	local_irq_restore(flags);
 }
 
-struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *s)
+struct pcpu_freelist_node *__pcpu_freelist_pop(struct pcpu_freelist *s)
 {
 	struct pcpu_freelist_head *head;
 	struct pcpu_freelist_node *node;
-	unsigned long flags;
 	int orig_cpu, cpu;
 
-	local_irq_save(flags);
 	orig_cpu = cpu = raw_smp_processor_id();
 	while (1) {
 		head = per_cpu_ptr(s->freelist, cpu);
@@ -89,16 +97,25 @@ struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *s)
 		node = head->first;
 		if (node) {
 			head->first = node->next;
-			raw_spin_unlock_irqrestore(&head->lock, flags);
+			raw_spin_unlock(&head->lock);
 			return node;
 		}
 		raw_spin_unlock(&head->lock);
 		cpu = cpumask_next(cpu, cpu_possible_mask);
 		if (cpu >= nr_cpu_ids)
 			cpu = 0;
-		if (cpu == orig_cpu) {
-			local_irq_restore(flags);
+		if (cpu == orig_cpu)
 			return NULL;
-		}
 	}
 }
+
+struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *s)
+{
+	struct pcpu_freelist_node *ret;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	ret = __pcpu_freelist_pop(s);
+	local_irq_restore(flags);
+	return ret;
+}

kernel/bpf/percpu_freelist.h

@@ -22,8 +22,12 @@ struct pcpu_freelist_node {
 	struct pcpu_freelist_node *next;
 };
 
+/* pcpu_freelist_* do spin_lock_irqsave. */
 void pcpu_freelist_push(struct pcpu_freelist *, struct pcpu_freelist_node *);
 struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *);
+/* __pcpu_freelist_* do spin_lock only. caller must disable irqs. */
+void __pcpu_freelist_push(struct pcpu_freelist *, struct pcpu_freelist_node *);
+struct pcpu_freelist_node *__pcpu_freelist_pop(struct pcpu_freelist *);
 void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
 			    u32 nr_elems);
 int pcpu_freelist_init(struct pcpu_freelist *);

kernel/bpf/syscall.c

@@ -713,8 +713,13 @@ static int map_lookup_elem(union bpf_attr *attr)
 
 	if (bpf_map_is_dev_bound(map)) {
 		err = bpf_map_offload_lookup_elem(map, key, value);
-	} else if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
-		   map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) {
+		goto done;
+	}
+
+	preempt_disable();
+	this_cpu_inc(bpf_prog_active);
+	if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
+	    map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) {
 		err = bpf_percpu_hash_copy(map, key, value);
 	} else if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY) {
 		err = bpf_percpu_array_copy(map, key, value);
@@ -744,7 +749,10 @@ static int map_lookup_elem(union bpf_attr *attr)
 		}
 		rcu_read_unlock();
 	}
+	this_cpu_dec(bpf_prog_active);
+	preempt_enable();
 
+done:
 	if (err)
 		goto free_value;
 

kernel/trace/bpf_trace.c

@@ -1204,22 +1204,12 @@ static int __bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *
 
 int bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *prog)
 {
-	int err;
-
-	mutex_lock(&bpf_event_mutex);
-	err = __bpf_probe_register(btp, prog);
-	mutex_unlock(&bpf_event_mutex);
-	return err;
+	return __bpf_probe_register(btp, prog);
 }
 
 int bpf_probe_unregister(struct bpf_raw_event_map *btp, struct bpf_prog *prog)
 {
-	int err;
-
-	mutex_lock(&bpf_event_mutex);
-	err = tracepoint_probe_unregister(btp->tp, (void *)btp->bpf_func, prog);
-	mutex_unlock(&bpf_event_mutex);
-	return err;
+	return tracepoint_probe_unregister(btp->tp, (void *)btp->bpf_func, prog);
 }
 
 int bpf_get_perf_event_info(const struct perf_event *event, u32 *prog_id,