tcp: remove volatile qualifier on tw_substate

Using a volatile qualifier for a specific struct field is unusual.

Use instead READ_ONCE()/WRITE_ONCE() where necessary.

tcp_timewait_state_process() can change tw_substate while other
threads are reading this field.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Link: https://patch.msgid.link/20240827015250.3509197-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h
index f88b682..beb533a 100644 (file)
--- a/include/net/inet_timewait_sock.h
+++ b/include/net/inet_timewait_sock.h
@@ -58,7 +58,7 @@ struct inet_timewait_sock {
 #define tw_dr                  __tw_common.skc_tw_dr
 
        __u32                   tw_mark;
-       volatile unsigned char  tw_substate;
+       unsigned char           tw_substate;
        unsigned char           tw_rcv_wscale;
 
        /* Socket demultiplex comparisons on incoming packets. */

diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 9712cdb..6763930 100644 (file)
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -442,7 +442,7 @@ static int inet_twsk_diag_fill(struct sock *sk,
        inet_diag_msg_common_fill(r, sk);
        r->idiag_retrans      = 0;
 
-       r->idiag_state        = tw->tw_substate;
+       r->idiag_state        = READ_ONCE(tw->tw_substate);
        r->idiag_timer        = 3;
        tmo = tw->tw_timer.expires - jiffies;
        r->idiag_expires      = jiffies_delta_to_msecs(tmo);
@@ -1209,7 +1209,7 @@ next_chunk:
                        if (num < s_num)
                                goto next_normal;
                        state = (sk->sk_state == TCP_TIME_WAIT) ?
-                               inet_twsk(sk)->tw_substate : sk->sk_state;
+                               READ_ONCE(inet_twsk(sk)->tw_substate) : sk->sk_state;
                        if (!(idiag_states & (1 << state)))
                                goto next_normal;
                        if (r->sdiag_family != AF_UNSPEC &&

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 5087e12..7c29158 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -120,7 +120,7 @@ int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
        struct tcp_sock *tp = tcp_sk(sk);
        int ts_recent_stamp;
 
-       if (tw->tw_substate == TCP_FIN_WAIT2)
+       if (READ_ONCE(tw->tw_substate) == TCP_FIN_WAIT2)
                reuse = 0;
 
        if (reuse == 2) {
@@ -2948,7 +2948,7 @@ static void get_timewait4_sock(const struct inet_timewait_sock *tw,
 
        seq_printf(f, "%4d: %08X:%04X %08X:%04X"
                " %02X %08X:%08X %02X:%08lX %08X %5d %8d %d %d %pK",
-               i, src, srcp, dest, destp, tw->tw_substate, 0, 0,
+               i, src, srcp, dest, destp, READ_ONCE(tw->tw_substate), 0, 0,
                3, jiffies_delta_to_clock_t(delta), 0, 0, 0, 0,
                refcount_read(&tw->tw_refcnt), tw);
 }

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index a19a9db..b6d547d 100644 (file)
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -117,7 +117,7 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
                }
        }
 
-       if (tw->tw_substate == TCP_FIN_WAIT2) {
+       if (READ_ONCE(tw->tw_substate) == TCP_FIN_WAIT2) {
                /* Just repeat all the checks of tcp_rcv_state_process() */
 
                /* Out of window, send ACK */
@@ -150,7 +150,7 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
                        return TCP_TW_RST;
 
                /* FIN arrived, enter true time-wait state. */
-               tw->tw_substate   = TCP_TIME_WAIT;
+               WRITE_ONCE(tw->tw_substate, TCP_TIME_WAIT);
                twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq);
 
                if (tmp_opt.saw_tstamp) {

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 200fea9..fb2e64c 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -2258,7 +2258,7 @@ static void get_timewait6_sock(struct seq_file *seq,
                   src->s6_addr32[2], src->s6_addr32[3], srcp,
                   dest->s6_addr32[0], dest->s6_addr32[1],
                   dest->s6_addr32[2], dest->s6_addr32[3], destp,
-                  tw->tw_substate, 0, 0,
+                  READ_ONCE(tw->tw_substate), 0, 0,
                   3, jiffies_delta_to_clock_t(delta), 0, 0, 0, 0,
                   refcount_read(&tw->tw_refcnt), tw);
 }