tcp: fix lockdep splat in tcp_snd_una_update()

tcp_snd_una_update() and tcp_rcv_nxt_update() call
u64_stats_update_begin() either from process context or BH handler.

This triggers a lockdep splat on 32bit & SMP builds.

We could add u64_stats_update_begin_bh() variant but this would
slow down 32bit builds with useless local_disable_bh() and
local_enable_bh() pairs, since we own the socket lock at this point.

I add sock_owned_by_me() helper to have proper lockdep support
even on 64bit builds, and new u64_stats_update_begin_raw()
and u64_stats_update_end_raw methods.

Fixes: c10d931 ("tcp: do not assume TCP code is non preemptible")
Reported-by: Fabio Estevam <festevam@gmail.com>
Diagnosed-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/u64_stats_sync.h

@@ -89,6 +89,20 @@ static inline void u64_stats_update_end(struct u64_stats_sync *syncp)
 #endif
 }
 
+static inline void u64_stats_update_begin_raw(struct u64_stats_sync *syncp)
+{
+#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+	raw_write_seqcount_begin(&syncp->seq);
+#endif
+}
+
+static inline void u64_stats_update_end_raw(struct u64_stats_sync *syncp)
+{
+#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+	raw_write_seqcount_end(&syncp->seq);
+#endif
+}
+
 static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
 {
 #if BITS_PER_LONG==32 && defined(CONFIG_SMP)

include/net/sock.h

@@ -1421,11 +1421,16 @@ static inline void unlock_sock_fast(struct sock *sk, bool slow)
  * accesses from user process context.
  */
 
-static inline bool sock_owned_by_user(const struct sock *sk)
+static inline void sock_owned_by_me(const struct sock *sk)
 {
 #ifdef CONFIG_LOCKDEP
 	WARN_ON_ONCE(!lockdep_sock_is_held(sk) && debug_locks);
 #endif
+}
+
+static inline bool sock_owned_by_user(const struct sock *sk)
+{
+	sock_owned_by_me(sk);
 	return sk->sk_lock.owned;
 }
 

net/ipv4/tcp_input.c

@@ -3355,9 +3355,10 @@ static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
 {
 	u32 delta = ack - tp->snd_una;
 
-	u64_stats_update_begin(&tp->syncp);
+	sock_owned_by_me((struct sock *)tp);
+	u64_stats_update_begin_raw(&tp->syncp);
 	tp->bytes_acked += delta;
-	u64_stats_update_end(&tp->syncp);
+	u64_stats_update_end_raw(&tp->syncp);
 	tp->snd_una = ack;
 }
 
@@ -3366,9 +3367,10 @@ static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
 {
 	u32 delta = seq - tp->rcv_nxt;
 
-	u64_stats_update_begin(&tp->syncp);
+	sock_owned_by_me((struct sock *)tp);
+	u64_stats_update_begin_raw(&tp->syncp);
 	tp->bytes_received += delta;
-	u64_stats_update_end(&tp->syncp);
+	u64_stats_update_end_raw(&tp->syncp);
 	tp->rcv_nxt = seq;
 }