bpf: Fix usage of trace RCU in local storage.

bpf_{sk,task,inode}_storage_free() do not need to use
call_rcu_tasks_trace as no BPF program should be accessing the owner
as it's being destroyed. The only other reader at this point is
bpf_local_storage_map_free() which uses normal RCU.

The only path that needs trace RCU are:

* bpf_local_storage_{delete,update} helpers
* map_{delete,update}_elem() syscalls

Fixes: 0fe4b381 ("bpf: Allow bpf_local_storage to be used by sleepable programs")
Signed-off-by: KP Singh <kpsingh@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220418155158.2865678-1-kpsingh@kernel.org

include/linux/bpf_local_storage.h

@@ -143,9 +143,9 @@ void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
 
 bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
 				     struct bpf_local_storage_elem *selem,
-				     bool uncharge_omem);
+				     bool uncharge_omem, bool use_trace_rcu);
 
-void bpf_selem_unlink(struct bpf_local_storage_elem *selem);
+void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool use_trace_rcu);
 
 void bpf_selem_link_map(struct bpf_local_storage_map *smap,
 			struct bpf_local_storage_elem *selem);

kernel/bpf/bpf_inode_storage.c

@@ -90,7 +90,7 @@ void bpf_inode_storage_free(struct inode *inode)
 		 */
 		bpf_selem_unlink_map(selem);
 		free_inode_storage = bpf_selem_unlink_storage_nolock(
-			local_storage, selem, false);
+			local_storage, selem, false, false);
 	}
 	raw_spin_unlock_bh(&local_storage->lock);
 	rcu_read_unlock();
@@ -149,7 +149,7 @@ static int inode_storage_delete(struct inode *inode, struct bpf_map *map)
 	if (!sdata)
 		return -ENOENT;
 
-	bpf_selem_unlink(SELEM(sdata));
+	bpf_selem_unlink(SELEM(sdata), true);
 
 	return 0;
 }

kernel/bpf/bpf_local_storage.c

@@ -106,7 +106,7 @@ static void bpf_selem_free_rcu(struct rcu_head *rcu)
  */
 bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
 				     struct bpf_local_storage_elem *selem,
-				     bool uncharge_mem)
+				     bool uncharge_mem, bool use_trace_rcu)
 {
 	struct bpf_local_storage_map *smap;
 	bool free_local_storage;
@@ -150,11 +150,16 @@ bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
 	    SDATA(selem))
 		RCU_INIT_POINTER(local_storage->cache[smap->cache_idx], NULL);
 
-	call_rcu_tasks_trace(&selem->rcu, bpf_selem_free_rcu);
+	if (use_trace_rcu)
+		call_rcu_tasks_trace(&selem->rcu, bpf_selem_free_rcu);
+	else
+		kfree_rcu(selem, rcu);
+
 	return free_local_storage;
 }
 
-static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem)
+static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem,
+				       bool use_trace_rcu)
 {
 	struct bpf_local_storage *local_storage;
 	bool free_local_storage = false;
@@ -169,12 +174,16 @@ static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem)
 	raw_spin_lock_irqsave(&local_storage->lock, flags);
 	if (likely(selem_linked_to_storage(selem)))
 		free_local_storage = bpf_selem_unlink_storage_nolock(
-			local_storage, selem, true);
+			local_storage, selem, true, use_trace_rcu);
 	raw_spin_unlock_irqrestore(&local_storage->lock, flags);
 
-	if (free_local_storage)
-		call_rcu_tasks_trace(&local_storage->rcu,
+	if (free_local_storage) {
+		if (use_trace_rcu)
+			call_rcu_tasks_trace(&local_storage->rcu,
 				     bpf_local_storage_free_rcu);
+		else
+			kfree_rcu(local_storage, rcu);
+	}
 }
 
 void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
@@ -214,14 +223,14 @@ void bpf_selem_link_map(struct bpf_local_storage_map *smap,
 	raw_spin_unlock_irqrestore(&b->lock, flags);
 }
 
-void bpf_selem_unlink(struct bpf_local_storage_elem *selem)
+void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool use_trace_rcu)
 {
 	/* Always unlink from map before unlinking from local_storage
 	 * because selem will be freed after successfully unlinked from
 	 * the local_storage.
 	 */
 	bpf_selem_unlink_map(selem);
-	__bpf_selem_unlink_storage(selem);
+	__bpf_selem_unlink_storage(selem, use_trace_rcu);
 }
 
 struct bpf_local_storage_data *
@@ -466,7 +475,7 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 	if (old_sdata) {
 		bpf_selem_unlink_map(SELEM(old_sdata));
 		bpf_selem_unlink_storage_nolock(local_storage, SELEM(old_sdata),
-						false);
+						false, true);
 	}
 
 unlock:
@@ -548,7 +557,7 @@ void bpf_local_storage_map_free(struct bpf_local_storage_map *smap,
 				migrate_disable();
 				__this_cpu_inc(*busy_counter);
 			}
-			bpf_selem_unlink(selem);
+			bpf_selem_unlink(selem, false);
 			if (busy_counter) {
 				__this_cpu_dec(*busy_counter);
 				migrate_enable();

kernel/bpf/bpf_task_storage.c

@@ -102,7 +102,7 @@ void bpf_task_storage_free(struct task_struct *task)
 		 */
 		bpf_selem_unlink_map(selem);
 		free_task_storage = bpf_selem_unlink_storage_nolock(
-			local_storage, selem, false);
+			local_storage, selem, false, false);
 	}
 	raw_spin_unlock_irqrestore(&local_storage->lock, flags);
 	bpf_task_storage_unlock();
@@ -192,7 +192,7 @@ static int task_storage_delete(struct task_struct *task, struct bpf_map *map)
 	if (!sdata)
 		return -ENOENT;
 
-	bpf_selem_unlink(SELEM(sdata));
+	bpf_selem_unlink(SELEM(sdata), true);
 
 	return 0;
 }

net/core/bpf_sk_storage.c

@@ -40,7 +40,7 @@ static int bpf_sk_storage_del(struct sock *sk, struct bpf_map *map)
 	if (!sdata)
 		return -ENOENT;
 
-	bpf_selem_unlink(SELEM(sdata));
+	bpf_selem_unlink(SELEM(sdata), true);
 
 	return 0;
 }
@@ -75,8 +75,8 @@ void bpf_sk_storage_free(struct sock *sk)
 		 * sk_storage.
 		 */
 		bpf_selem_unlink_map(selem);
-		free_sk_storage = bpf_selem_unlink_storage_nolock(sk_storage,
-								  selem, true);
+		free_sk_storage = bpf_selem_unlink_storage_nolock(
+			sk_storage, selem, true, false);
 	}
 	raw_spin_unlock_bh(&sk_storage->lock);
 	rcu_read_unlock();