netdev - [PATCH net-next 04/18] ipv6: sr: Use nested-BH locking for hmac

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Message-ID: <20250309144653.825351-5-bigeasy@linutronix.de>
Date: Sun,  9 Mar 2025 15:46:39 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: netdev@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	David Ahern <dsahern@...nel.org>
Subject: [PATCH net-next 04/18] ipv6: sr: Use nested-BH locking for hmac_storage.

hmac_storage 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.

Cc: David Ahern <dsahern@...nel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 net/ipv6/seg6_hmac.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/seg6_hmac.c b/net/ipv6/seg6_hmac.c
index bbf5b84a70fca..f78ecb6ad8383 100644
--- a/net/ipv6/seg6_hmac.c
+++ b/net/ipv6/seg6_hmac.c
@@ -40,7 +40,14 @@
 #include <net/seg6_hmac.h>
 #include <linux/random.h>
 
-static DEFINE_PER_CPU(char [SEG6_HMAC_RING_SIZE], hmac_ring);
+struct hmac_storage {
+	local_lock_t bh_lock;
+	char hmac_ring[SEG6_HMAC_RING_SIZE];
+};
+
+static DEFINE_PER_CPU(struct hmac_storage, hmac_storage) = {
+	.bh_lock = INIT_LOCAL_LOCK(bh_lock),
+};
 
 static int seg6_hmac_cmpfn(struct rhashtable_compare_arg *arg, const void *obj)
 {
@@ -187,7 +194,8 @@ int seg6_hmac_compute(struct seg6_hmac_info *hinfo, struct ipv6_sr_hdr *hdr,
 	 */
 
 	local_bh_disable();
-	ring = this_cpu_ptr(hmac_ring);
+	local_lock_nested_bh(&hmac_storage.bh_lock);
+	ring = this_cpu_ptr(hmac_storage.hmac_ring);
 	off = ring;
 
 	/* source address */
@@ -212,6 +220,7 @@ int seg6_hmac_compute(struct seg6_hmac_info *hinfo, struct ipv6_sr_hdr *hdr,
 
 	dgsize = __do_hmac(hinfo, ring, plen, tmp_out,
 			   SEG6_HMAC_MAX_DIGESTSIZE);
+	local_unlock_nested_bh(&hmac_storage.bh_lock);
 	local_bh_enable();
 
 	if (dgsize < 0)
-- 
2.47.2