tcp_metrics: annotate data-races around tm->tcpm_stamp

tm->tcpm_stamp can be read or written locklessly.

Add needed READ_ONCE()/WRITE_ONCE() to document this.

Also constify tcpm_check_stamp() dst argument.

Fixes: 51c5d0c4b169 ("tcp: Maintain dynamic metrics in local cache.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230802131500.1478140-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index c4daf0aa2d4d9695e128b67df571d91d647a254d..83861658879638149d2746290a285a4f75fc3117 100644 (file)
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -97,7 +97,7 @@ static void tcpm_suck_dst(struct tcp_metrics_block *tm,
        u32 msval;
        u32 val;
 
-       tm->tcpm_stamp = jiffies;
+       WRITE_ONCE(tm->tcpm_stamp, jiffies);
 
        val = 0;
        if (dst_metric_locked(dst, RTAX_RTT))
@@ -131,9 +131,15 @@ static void tcpm_suck_dst(struct tcp_metrics_block *tm,
 
 #define TCP_METRICS_TIMEOUT            (60 * 60 * HZ)
 
-static void tcpm_check_stamp(struct tcp_metrics_block *tm, struct dst_entry *dst)
+static void tcpm_check_stamp(struct tcp_metrics_block *tm,
+                            const struct dst_entry *dst)
 {
-       if (tm && unlikely(time_after(jiffies, tm->tcpm_stamp + TCP_METRICS_TIMEOUT)))
+       unsigned long limit;
+
+       if (!tm)
+               return;
+       limit = READ_ONCE(tm->tcpm_stamp) + TCP_METRICS_TIMEOUT;
+       if (unlikely(time_after(jiffies, limit)))
                tcpm_suck_dst(tm, dst, false);
 }
 
@@ -174,7 +180,8 @@ static struct tcp_metrics_block *tcpm_new(struct dst_entry *dst,
                oldest = deref_locked(tcp_metrics_hash[hash].chain);
                for (tm = deref_locked(oldest->tcpm_next); tm;
                     tm = deref_locked(tm->tcpm_next)) {
-                       if (time_before(tm->tcpm_stamp, oldest->tcpm_stamp))
+                       if (time_before(READ_ONCE(tm->tcpm_stamp),
+                                       READ_ONCE(oldest->tcpm_stamp)))
                                oldest = tm;
                }
                tm = oldest;
@@ -434,7 +441,7 @@ void tcp_update_metrics(struct sock *sk)
                                               tp->reordering);
                }
        }
-       tm->tcpm_stamp = jiffies;
+       WRITE_ONCE(tm->tcpm_stamp, jiffies);
 out_unlock:
        rcu_read_unlock();
 }
@@ -647,7 +654,7 @@ static int tcp_metrics_fill_info(struct sk_buff *msg,
        }
 
        if (nla_put_msecs(msg, TCP_METRICS_ATTR_AGE,
-                         jiffies - tm->tcpm_stamp,
+                         jiffies - READ_ONCE(tm->tcpm_stamp),
                          TCP_METRICS_ATTR_PAD) < 0)
                goto nla_put_failure;