netfilter: conntrack: Use sequence counter with associated spinlock

A sequence counter write side critical section must be protected by some
form of locking to serialize writers. A plain seqcount_t does not
contain the information of which lock must be held when entering a write
side critical section.

Use the new seqcount_spinlock_t data type, which allows to associate a
spinlock with the sequence counter. This enables lockdep to verify that
the spinlock used for writer serialization is held when the write side
critical section is entered.

If lockdep is disabled this lock association is compiled out and has
neither storage size nor runtime overhead.

Signed-off-by: Ahmed S. Darwish <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: a-darwish

include/net/netfilter/nf_conntrack.h

@@ -286,7 +286,7 @@ int nf_conntrack_hash_resize(unsigned int hashsize);
 
 extern struct hlist_nulls_head *nf_conntrack_hash;
 extern unsigned int nf_conntrack_htable_size;
-extern seqcount_t nf_conntrack_generation;
+extern seqcount_spinlock_t nf_conntrack_generation;
 extern unsigned int nf_conntrack_max;
 
 /* must be called with rcu read lock held */

net/netfilter/nf_conntrack_core.c

@@ -180,7 +180,7 @@ EXPORT_SYMBOL_GPL(nf_conntrack_htable_size);
 
 unsigned int nf_conntrack_max __read_mostly;
 EXPORT_SYMBOL_GPL(nf_conntrack_max);
-seqcount_t nf_conntrack_generation __read_mostly;
+seqcount_spinlock_t nf_conntrack_generation __read_mostly;
 static unsigned int nf_conntrack_hash_rnd __read_mostly;
 
 static u32 hash_conntrack_raw(const struct nf_conntrack_tuple *tuple,
@@ -2600,7 +2600,8 @@ int nf_conntrack_init_start(void)
 	/* struct nf_ct_ext uses u8 to store offsets/size */
 	BUILD_BUG_ON(total_extension_size() > 255u);
 
-	seqcount_init(&nf_conntrack_generation);
+	seqcount_spinlock_init(&nf_conntrack_generation,
+			       &nf_conntrack_locks_all_lock);
 
 	for (i = 0; i < CONNTRACK_LOCKS; i++)
 		spin_lock_init(&nf_conntrack_locks[i]);