Re: [PATCH v5 net-next 14/15] net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.

[Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>]

On 2024-06-11 10:39:20 [+0200], To Jesper Dangaard Brouer wrote:
> On 2024-06-11 09:55:11 [+0200], Jesper Dangaard Brouer wrote:
> > >   struct bpf_net_context {
> > >   	struct bpf_redirect_info ri;
> > >   	struct list_head cpu_map_flush_list;
> > >   	struct list_head dev_map_flush_list;
> > >   	struct list_head xskmap_map_flush_list;
> > > +	unsigned int flags;
> > 
> > Why have yet another flags variable, when we already have two flags in
> > bpf_redirect_info ?
> 
> Ah you want to fold this into ri member including the status for the
> lists? Could try. It is splitted in order to delay the initialisation of
> the lists, too. We would need to be careful to not overwrite the
> flags if `ri' is initialized after the lists. That would be the case
> with CONFIG_DEBUG_NET=y and not doing redirect (the empty list check
> initializes that).

What about this:

------>8----------

diff --git a/include/linux/filter.h b/include/linux/filter.h
index d2b4260d9d0be..c0349522de8fb 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -733,15 +733,22 @@ struct bpf_nh_params {
 	};
 };
 
+/* flags for bpf_redirect_info kern_flags */
+#define BPF_RI_F_RF_NO_DIRECT	BIT(0)	/* no napi_direct on return_frame */
+#define BPF_RI_F_RI_INIT	BIT(1)
+#define BPF_RI_F_CPU_MAP_INIT	BIT(2)
+#define BPF_RI_F_DEV_MAP_INIT	BIT(3)
+#define BPF_RI_F_XSK_MAP_INIT	BIT(4)
+
 struct bpf_redirect_info {
 	u64 tgt_index;
 	void *tgt_value;
 	struct bpf_map *map;
 	u32 flags;
-	u32 kern_flags;
 	u32 map_id;
 	enum bpf_map_type map_type;
 	struct bpf_nh_params nh;
+	u32 kern_flags;
 };
 
 struct bpf_net_context {
@@ -757,14 +764,7 @@ static inline struct bpf_net_context *bpf_net_ctx_set(struct bpf_net_context *bp
 
 	if (tsk->bpf_net_context != NULL)
 		return NULL;
-	memset(&bpf_net_ctx->ri, 0, sizeof(bpf_net_ctx->ri));
-
-	if (IS_ENABLED(CONFIG_BPF_SYSCALL)) {
-		INIT_LIST_HEAD(&bpf_net_ctx->cpu_map_flush_list);
-		INIT_LIST_HEAD(&bpf_net_ctx->dev_map_flush_list);
-	}
-	if (IS_ENABLED(CONFIG_XDP_SOCKETS))
-		INIT_LIST_HEAD(&bpf_net_ctx->xskmap_map_flush_list);
+	bpf_net_ctx->ri.kern_flags = 0;
 
 	tsk->bpf_net_context = bpf_net_ctx;
 	return bpf_net_ctx;
@@ -785,6 +785,11 @@ static inline struct bpf_redirect_info *bpf_net_ctx_get_ri(void)
 {
 	struct bpf_net_context *bpf_net_ctx = bpf_net_ctx_get();
 
+	if (!(bpf_net_ctx->ri.kern_flags & BPF_RI_F_RI_INIT)) {
+		memset(&bpf_net_ctx->ri, 0, offsetof(struct bpf_net_context, ri.nh));
+		bpf_net_ctx->ri.kern_flags |= BPF_RI_F_RI_INIT;
+	}
+
 	return &bpf_net_ctx->ri;
 }
 
@@ -792,6 +797,11 @@ static inline struct list_head *bpf_net_ctx_get_cpu_map_flush_list(void)
 {
 	struct bpf_net_context *bpf_net_ctx = bpf_net_ctx_get();
 
+	if (!(bpf_net_ctx->ri.kern_flags & BPF_RI_F_CPU_MAP_INIT)) {
+		INIT_LIST_HEAD(&bpf_net_ctx->cpu_map_flush_list);
+		bpf_net_ctx->ri.kern_flags |= BPF_RI_F_CPU_MAP_INIT;
+	}
+
 	return &bpf_net_ctx->cpu_map_flush_list;
 }
 
@@ -799,6 +809,11 @@ static inline struct list_head *bpf_net_ctx_get_dev_flush_list(void)
 {
 	struct bpf_net_context *bpf_net_ctx = bpf_net_ctx_get();
 
+	if (!(bpf_net_ctx->ri.kern_flags & BPF_RI_F_DEV_MAP_INIT)) {
+		INIT_LIST_HEAD(&bpf_net_ctx->dev_map_flush_list);
+		bpf_net_ctx->ri.kern_flags |= BPF_RI_F_DEV_MAP_INIT;
+	}
+
 	return &bpf_net_ctx->dev_map_flush_list;
 }
 
@@ -806,12 +821,14 @@ static inline struct list_head *bpf_net_ctx_get_xskmap_flush_list(void)
 {
 	struct bpf_net_context *bpf_net_ctx = bpf_net_ctx_get();
 
+	if (!(bpf_net_ctx->ri.kern_flags & BPF_RI_F_XSK_MAP_INIT)) {
+		INIT_LIST_HEAD(&bpf_net_ctx->xskmap_map_flush_list);
+		bpf_net_ctx->ri.kern_flags |= BPF_RI_F_XSK_MAP_INIT;
+	}
+
 	return &bpf_net_ctx->xskmap_map_flush_list;
 }
 
-/* flags for bpf_redirect_info kern_flags */
-#define BPF_RI_F_RF_NO_DIRECT	BIT(0)	/* no napi_direct on return_frame */
-
 /* Compute the linear packet data range [data, data_end) which
  * will be accessed by various program types (cls_bpf, act_bpf,
  * lwt, ...). Subsystems allowing direct data access must (!)

------>8----------

Moving kern_flags to the end excludes it from the memset() and can be
re-used for the delayed initialisation.

Sebastian