xdp: Use nested-BH locking for system_page_pool

system_page_pool is a per-CPU variable and relies on disabled BH for its
locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT
this data structure requires explicit locking.

Make a struct with a page_pool member (original system_page_pool) and a
local_lock_t and use local_lock_nested_bh() for locking. This change
adds only lockdep coverage and does not alter the functional behaviour
for !PREEMPT_RT.

Cc: Andrew Lunn <andrew+netdev@lunn.ch>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jesper Dangaard Brouer <hawk@kernel.org>
Cc: John Fastabend <john.fastabend@gmail.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20250512092736.229935-6-bigeasy@linutronix.de
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 9e3a2d8452d6806a0bc0ef022a026c844c904def..73a97cf1bbce3bc4f3fbcd0459dc70e39518a79f 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3503,7 +3503,12 @@ struct softnet_data {
 };
 
 DECLARE_PER_CPU_ALIGNED(struct softnet_data, softnet_data);
-DECLARE_PER_CPU(struct page_pool *, system_page_pool);
+
+struct page_pool_bh {
+       struct page_pool *pool;
+       local_lock_t bh_lock;
+};
+DECLARE_PER_CPU(struct page_pool_bh, system_page_pool);
 
 #ifndef CONFIG_PREEMPT_RT
 static inline int dev_recursion_level(void)

diff --git a/net/core/dev.c b/net/core/dev.c
index 33d5e95209cb41496f5c82423d01890fc9fe78df..eea26162a58556025afea940a34a4fd0c563acbe 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -462,7 +462,9 @@ EXPORT_PER_CPU_SYMBOL(softnet_data);
  * PP consumers must pay attention to run APIs in the appropriate context
  * (e.g. NAPI context).
  */
-DEFINE_PER_CPU(struct page_pool *, system_page_pool);
+DEFINE_PER_CPU(struct page_pool_bh, system_page_pool) = {
+       .bh_lock = INIT_LOCAL_LOCK(bh_lock),
+};
 
 #ifdef CONFIG_LOCKDEP
 /*
@@ -5322,7 +5324,10 @@ netif_skb_check_for_xdp(struct sk_buff **pskb, const struct bpf_prog *prog)
        struct sk_buff *skb = *pskb;
        int err, hroom, troom;
 
-       if (!skb_cow_data_for_xdp(this_cpu_read(system_page_pool), pskb, prog))
+       local_lock_nested_bh(&system_page_pool.bh_lock);
+       err = skb_cow_data_for_xdp(this_cpu_read(system_page_pool.pool), pskb, prog);
+       local_unlock_nested_bh(&system_page_pool.bh_lock);
+       if (!err)
                return 0;
 
        /* In case we have to go down the path and also linearize,
@@ -12712,7 +12717,7 @@ static int net_page_pool_create(int cpuid)
                return err;
        }
 
-       per_cpu(system_page_pool, cpuid) = pp_ptr;
+       per_cpu(system_page_pool.pool, cpuid) = pp_ptr;
 #endif
        return 0;
 }
@@ -12842,13 +12847,13 @@ out:
                for_each_possible_cpu(i) {
                        struct page_pool *pp_ptr;
 
-                       pp_ptr = per_cpu(system_page_pool, i);
+                       pp_ptr = per_cpu(system_page_pool.pool, i);
                        if (!pp_ptr)
                                continue;
 
                        xdp_unreg_page_pool(pp_ptr);
                        page_pool_destroy(pp_ptr);
-                       per_cpu(system_page_pool, i) = NULL;
+                       per_cpu(system_page_pool.pool, i) = NULL;
                }
        }
 

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 4e91c779067112fd6dc6856f9401c644a9ca697d..e6f22ba61c1ea9479ef6ecb36c16f74a88785c8f 100644 (file)
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -739,25 +739,27 @@ static noinline bool xdp_copy_frags_from_zc(struct sk_buff *skb,
  */
 struct sk_buff *xdp_build_skb_from_zc(struct xdp_buff *xdp)
 {
-       struct page_pool *pp = this_cpu_read(system_page_pool);
        const struct xdp_rxq_info *rxq = xdp->rxq;
        u32 len = xdp->data_end - xdp->data_meta;
        u32 truesize = xdp->frame_sz;
-       struct sk_buff *skb;
+       struct sk_buff *skb = NULL;
+       struct page_pool *pp;
        int metalen;
        void *data;
 
        if (!IS_ENABLED(CONFIG_PAGE_POOL))
                return NULL;
 
+       local_lock_nested_bh(&system_page_pool.bh_lock);
+       pp = this_cpu_read(system_page_pool.pool);
        data = page_pool_dev_alloc_va(pp, &truesize);
        if (unlikely(!data))
-               return NULL;
+               goto out;
 
        skb = napi_build_skb(data, truesize);
        if (unlikely(!skb)) {
                page_pool_free_va(pp, data, true);
-               return NULL;
+               goto out;
        }
 
        skb_mark_for_recycle(skb);
@@ -776,13 +778,16 @@ struct sk_buff *xdp_build_skb_from_zc(struct xdp_buff *xdp)
        if (unlikely(xdp_buff_has_frags(xdp)) &&
            unlikely(!xdp_copy_frags_from_zc(skb, xdp, pp))) {
                napi_consume_skb(skb, true);
-               return NULL;
+               skb = NULL;
+               goto out;
        }
 
        xsk_buff_free(xdp);
 
        skb->protocol = eth_type_trans(skb, rxq->dev);
 
+out:
+       local_unlock_nested_bh(&system_page_pool.bh_lock);
        return skb;
 }
 EXPORT_SYMBOL_GPL(xdp_build_skb_from_zc);