1 files changed, 26 insertions, 20 deletions

diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c
index 4376016f7fa5..7092a61c4dc8 100644
--- a/net/ipv4/tcp_dctcp.c
+++ b/net/ipv4/tcp_dctcp.c
@@ -204,20 +204,26 @@ static void dctcp_update_alpha(struct sock *sk, u32 flags)
 
 	/* Expired RTT */
 	if (!before(tp->snd_una, ca->next_seq)) {
-		/* For avoiding denominator == 1. */
-		if (ca->acked_bytes_total == 0)
-			ca->acked_bytes_total = 1;
+		u64 bytes_ecn = ca->acked_bytes_ecn;
+		u32 alpha = ca->dctcp_alpha;
 
 		/* alpha = (1 - g) * alpha + g * F */
-		ca->dctcp_alpha = ca->dctcp_alpha -
-				  (ca->dctcp_alpha >> dctcp_shift_g) +
-				  (ca->acked_bytes_ecn << (10U - dctcp_shift_g)) /
-				  ca->acked_bytes_total;
 
-		if (ca->dctcp_alpha > DCTCP_MAX_ALPHA)
-			/* Clamp dctcp_alpha to max. */
-			ca->dctcp_alpha = DCTCP_MAX_ALPHA;
+		alpha -= alpha >> dctcp_shift_g;
+		if (bytes_ecn) {
+			/* If dctcp_shift_g == 1, a 32bit value would overflow
+			 * after 8 Mbytes.
+			 */
+			bytes_ecn <<= (10 - dctcp_shift_g);
+			do_div(bytes_ecn, max(1U, ca->acked_bytes_total));
 
+			alpha = min(alpha + (u32)bytes_ecn, DCTCP_MAX_ALPHA);
+		}
+		/* dctcp_alpha can be read from dctcp_get_info() without
+		 * synchro, so we ask compiler to not use dctcp_alpha
+		 * as a temporary variable in prior operations.
+		 */
+		WRITE_ONCE(ca->dctcp_alpha, alpha);
 		dctcp_reset(tp, ca);
 	}
 }
@@ -277,7 +283,8 @@ static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev)
 	}
 }
 
-static int dctcp_get_info(struct sock *sk, u32 ext, struct sk_buff *skb)
+static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr,
+			     union tcp_cc_info *info)
 {
 	const struct dctcp *ca = inet_csk_ca(sk);
 
@@ -286,18 +293,17 @@ static int dctcp_get_info(struct sock *sk, u32 ext, struct sk_buff *skb)
 	 */
 	if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) ||
 	    ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
-		struct tcp_dctcp_info info;
-
-		memset(&info, 0, sizeof(info));
+		memset(info, 0, sizeof(struct tcp_dctcp_info));
 		if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) {
-			info.dctcp_enabled = 1;
-			info.dctcp_ce_state = (u16) ca->ce_state;
-			info.dctcp_alpha = ca->dctcp_alpha;
-			info.dctcp_ab_ecn = ca->acked_bytes_ecn;
-			info.dctcp_ab_tot = ca->acked_bytes_total;
+			info->dctcp.dctcp_enabled = 1;
+			info->dctcp.dctcp_ce_state = (u16) ca->ce_state;
+			info->dctcp.dctcp_alpha = ca->dctcp_alpha;
+			info->dctcp.dctcp_ab_ecn = ca->acked_bytes_ecn;
+			info->dctcp.dctcp_ab_tot = ca->acked_bytes_total;
 		}
 
-		return nla_put(skb, INET_DIAG_DCTCPINFO, sizeof(info), &info);
+		*attr = INET_DIAG_DCTCPINFO;
+		return sizeof(*info);
 	}
 	return 0;
 }