net: dst_cache: Use nested-BH locking for dst_cache::cache

dst_cache::cache 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@linutronix.de>
Link: https://patch.msgid.link/20250512092736.229935-3-bigeasy@linutronix.de
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/core/dst_cache.c b/net/core/dst_cache.c
index 70c634b9e7b02300188582a1634d5977838db132..93a04d18e50541dc43d8ddd062d10d7c41907057 100644 (file)
--- a/net/core/dst_cache.c
+++ b/net/core/dst_cache.c
@@ -17,6 +17,7 @@
 struct dst_cache_pcpu {
        unsigned long refresh_ts;
        struct dst_entry *dst;
+       local_lock_t bh_lock;
        u32 cookie;
        union {
                struct in_addr in_saddr;
@@ -65,10 +66,15 @@ fail:
 
 struct dst_entry *dst_cache_get(struct dst_cache *dst_cache)
 {
+       struct dst_entry *dst;
+
        if (!dst_cache->cache)
                return NULL;
 
-       return dst_cache_per_cpu_get(dst_cache, this_cpu_ptr(dst_cache->cache));
+       local_lock_nested_bh(&dst_cache->cache->bh_lock);
+       dst = dst_cache_per_cpu_get(dst_cache, this_cpu_ptr(dst_cache->cache));
+       local_unlock_nested_bh(&dst_cache->cache->bh_lock);
+       return dst;
 }
 EXPORT_SYMBOL_GPL(dst_cache_get);
 
@@ -80,12 +86,16 @@ struct rtable *dst_cache_get_ip4(struct dst_cache *dst_cache, __be32 *saddr)
        if (!dst_cache->cache)
                return NULL;
 
+       local_lock_nested_bh(&dst_cache->cache->bh_lock);
        idst = this_cpu_ptr(dst_cache->cache);
        dst = dst_cache_per_cpu_get(dst_cache, idst);
-       if (!dst)
+       if (!dst) {
+               local_unlock_nested_bh(&dst_cache->cache->bh_lock);
                return NULL;
+       }
 
        *saddr = idst->in_saddr.s_addr;
+       local_unlock_nested_bh(&dst_cache->cache->bh_lock);
        return dst_rtable(dst);
 }
 EXPORT_SYMBOL_GPL(dst_cache_get_ip4);
@@ -98,9 +108,11 @@ void dst_cache_set_ip4(struct dst_cache *dst_cache, struct dst_entry *dst,
        if (!dst_cache->cache)
                return;
 
+       local_lock_nested_bh(&dst_cache->cache->bh_lock);
        idst = this_cpu_ptr(dst_cache->cache);
        dst_cache_per_cpu_dst_set(idst, dst, 0);
        idst->in_saddr.s_addr = saddr;
+       local_unlock_nested_bh(&dst_cache->cache->bh_lock);
 }
 EXPORT_SYMBOL_GPL(dst_cache_set_ip4);
 
@@ -113,10 +125,13 @@ void dst_cache_set_ip6(struct dst_cache *dst_cache, struct dst_entry *dst,
        if (!dst_cache->cache)
                return;
 
+       local_lock_nested_bh(&dst_cache->cache->bh_lock);
+
        idst = this_cpu_ptr(dst_cache->cache);
        dst_cache_per_cpu_dst_set(idst, dst,
                                  rt6_get_cookie(dst_rt6_info(dst)));
        idst->in6_saddr = *saddr;
+       local_unlock_nested_bh(&dst_cache->cache->bh_lock);
 }
 EXPORT_SYMBOL_GPL(dst_cache_set_ip6);
 
@@ -129,12 +144,17 @@ struct dst_entry *dst_cache_get_ip6(struct dst_cache *dst_cache,
        if (!dst_cache->cache)
                return NULL;
 
+       local_lock_nested_bh(&dst_cache->cache->bh_lock);
+
        idst = this_cpu_ptr(dst_cache->cache);
        dst = dst_cache_per_cpu_get(dst_cache, idst);
-       if (!dst)
+       if (!dst) {
+               local_unlock_nested_bh(&dst_cache->cache->bh_lock);
                return NULL;
+       }
 
        *saddr = idst->in6_saddr;
+       local_unlock_nested_bh(&dst_cache->cache->bh_lock);
        return dst;
 }
 EXPORT_SYMBOL_GPL(dst_cache_get_ip6);
@@ -142,10 +162,14 @@ EXPORT_SYMBOL_GPL(dst_cache_get_ip6);
 
 int dst_cache_init(struct dst_cache *dst_cache, gfp_t gfp)
 {
+       unsigned int i;
+
        dst_cache->cache = alloc_percpu_gfp(struct dst_cache_pcpu,
                                            gfp | __GFP_ZERO);
        if (!dst_cache->cache)
                return -ENOMEM;
+       for_each_possible_cpu(i)
+               local_lock_init(&per_cpu_ptr(dst_cache->cache, i)->bh_lock);
 
        dst_cache_reset(dst_cache);
        return 0;