netdev - [PATCH net-next 6/6] netfilter: nft_set_pipapo: Use nested-BH locking for nft_pipapo

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Message-ID: <20250820144738.24250-7-fw@strlen.de>
Date: Wed, 20 Aug 2025 16:47:38 +0200
From: Florian Westphal <fw@...len.de>
To: <netdev@...r.kernel.org>
Cc: Paolo Abeni <pabeni@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	<netfilter-devel@...r.kernel.org>,
	pablo@...filter.org,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH net-next 6/6] netfilter: nft_set_pipapo: Use nested-BH locking for nft_pipapo_scratch

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

nft_pipapo_scratch 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.

Add a local_lock_t to the data structure and use local_lock_nested_bh() for
locking. This change adds only lockdep coverage and does not alter the
functional behaviour for !PREEMPT_RT.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/netfilter/nft_set_pipapo.c      | 5 +++++
 net/netfilter/nft_set_pipapo.h      | 2 ++
 net/netfilter/nft_set_pipapo_avx2.c | 4 ++++
 3 files changed, 11 insertions(+)

diff --git a/net/netfilter/nft_set_pipapo.c b/net/netfilter/nft_set_pipapo.c
index 96b7539f5506..b385cfcf886f 100644
--- a/net/netfilter/nft_set_pipapo.c
+++ b/net/netfilter/nft_set_pipapo.c
@@ -429,6 +429,7 @@ static struct nft_pipapo_elem *pipapo_get_slow(const struct nft_pipapo_match *m,
 	scratch = *raw_cpu_ptr(m->scratch);
 	if (unlikely(!scratch))
 		goto out;
+	__local_lock_nested_bh(&scratch->bh_lock);
 
 	map_index = scratch->map_index;
 
@@ -465,6 +466,7 @@ static struct nft_pipapo_elem *pipapo_get_slow(const struct nft_pipapo_match *m,
 				  last);
 		if (b < 0) {
 			scratch->map_index = map_index;
+			__local_unlock_nested_bh(&scratch->bh_lock);
 			local_bh_enable();
 
 			return NULL;
@@ -484,6 +486,7 @@ static struct nft_pipapo_elem *pipapo_get_slow(const struct nft_pipapo_match *m,
 			 * *next* bitmap (not initial) for the next packet.
 			 */
 			scratch->map_index = map_index;
+			__local_unlock_nested_bh(&scratch->bh_lock);
 			local_bh_enable();
 			return e;
 		}
@@ -498,6 +501,7 @@ static struct nft_pipapo_elem *pipapo_get_slow(const struct nft_pipapo_match *m,
 		data += NFT_PIPAPO_GROUPS_PADDING(f);
 	}
 
+	__local_unlock_nested_bh(&scratch->bh_lock);
 out:
 	local_bh_enable();
 	return NULL;
@@ -1215,6 +1219,7 @@ static int pipapo_realloc_scratch(struct nft_pipapo_match *clone,
 		}
 
 		pipapo_free_scratch(clone, i);
+		local_lock_init(&scratch->bh_lock);
 		*per_cpu_ptr(clone->scratch, i) = scratch;
 	}
 
diff --git a/net/netfilter/nft_set_pipapo.h b/net/netfilter/nft_set_pipapo.h
index e10cdbaa65d8..eaab422aa56a 100644
--- a/net/netfilter/nft_set_pipapo.h
+++ b/net/netfilter/nft_set_pipapo.h
@@ -124,10 +124,12 @@ struct nft_pipapo_field {
 
 /**
  * struct nft_pipapo_scratch - percpu data used for lookup and matching
+ * @bh_lock:    PREEMPT_RT local spinlock
  * @map_index:	Current working bitmap index, toggled between field matches
  * @__map:	store partial matching results during lookup
  */
 struct nft_pipapo_scratch {
+	local_lock_t bh_lock;
 	u8 map_index;
 	unsigned long __map[];
 };
diff --git a/net/netfilter/nft_set_pipapo_avx2.c b/net/netfilter/nft_set_pipapo_avx2.c
index f0d8c796d731..29326f3fcaf3 100644
--- a/net/netfilter/nft_set_pipapo_avx2.c
+++ b/net/netfilter/nft_set_pipapo_avx2.c
@@ -1163,6 +1163,7 @@ struct nft_pipapo_elem *pipapo_get_avx2(const struct nft_pipapo_match *m,
 	if (unlikely(!scratch))
 		return NULL;
 
+	__local_lock_nested_bh(&scratch->bh_lock);
 	map_index = scratch->map_index;
 	map = NFT_PIPAPO_LT_ALIGN(&scratch->__map[0]);
 	res  = map + (map_index ? m->bsize_max : 0);
@@ -1228,6 +1229,7 @@ struct nft_pipapo_elem *pipapo_get_avx2(const struct nft_pipapo_match *m,
 		if (ret < 0) {
 			scratch->map_index = map_index;
 			kernel_fpu_end();
+			__local_unlock_nested_bh(&scratch->bh_lock);
 			return NULL;
 		}
 
@@ -1241,6 +1243,7 @@ struct nft_pipapo_elem *pipapo_get_avx2(const struct nft_pipapo_match *m,
 
 			scratch->map_index = map_index;
 			kernel_fpu_end();
+			__local_unlock_nested_bh(&scratch->bh_lock);
 			return e;
 		}
 
@@ -1250,6 +1253,7 @@ struct nft_pipapo_elem *pipapo_get_avx2(const struct nft_pipapo_match *m,
 	}
 
 	kernel_fpu_end();
+	__local_unlock_nested_bh(&scratch->bh_lock);
 	return NULL;
 }
 
-- 
2.49.1