selftests: fix OOM in msg_zerocopy selftest

In selftests/net/msg_zerocopy.c, it has a while loop keeps calling sendmsg
on a socket with MSG_ZEROCOPY flag, and it will recv the notifications
until the socket is not writable. Typically, it will start the receiving
process after around 30+ sendmsgs. However, as the introduction of commit
dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale"), the sender is
always writable and does not get any chance to run recv notifications.
The selftest always exits with OUT_OF_MEMORY because the memory used by
opt_skb exceeds the net.core.optmem_max. Meanwhile, it could be set to a
different value to trigger OOM on older kernels too.

Thus, we introduce "cfg_notification_limit" to force sender to receive
notifications after some number of sendmsgs.

Fixes: 07b65c5b31ce ("test: add msg_zerocopy test")
Signed-off-by: Zijian Zhang <zijianzhang@bytedance.com>
Signed-off-by: Xiaochun Lu <xiaochun.lu@bytedance.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20240701225349.3395580-2-zijianzhang@bytedance.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/tools/testing/selftests/net/msg_zerocopy.c b/tools/testing/selftests/net/msg_zerocopy.c
index bdc03a2097e85a91550ef9be7f283beb1dab0ec4..926556febc83ce38ef0b3c3bb296ad22e04db142 100644 (file)
--- a/tools/testing/selftests/net/msg_zerocopy.c
+++ b/tools/testing/selftests/net/msg_zerocopy.c
@@ -85,6 +85,7 @@ static bool cfg_rx;
 static int  cfg_runtime_ms     = 4200;
 static int  cfg_verbose;
 static int  cfg_waittime_ms    = 500;
+static int  cfg_notification_limit = 32;
 static bool cfg_zerocopy;
 
 static socklen_t cfg_alen;
@@ -95,6 +96,7 @@ static char payload[IP_MAXPACKET];
 static long packets, bytes, completions, expected_completions;
 static int  zerocopied = -1;
 static uint32_t next_completion;
+static uint32_t sends_since_notify;
 
 static unsigned long gettimeofday_ms(void)
 {
@@ -208,6 +210,7 @@ static bool do_sendmsg(int fd, struct msghdr *msg, bool do_zerocopy, int domain)
                error(1, errno, "send");
        if (cfg_verbose && ret != len)
                fprintf(stderr, "send: ret=%u != %u\n", ret, len);
+       sends_since_notify++;
 
        if (len) {
                packets++;
@@ -460,6 +463,7 @@ static bool do_recv_completion(int fd, int domain)
 static void do_recv_completions(int fd, int domain)
 {
        while (do_recv_completion(fd, domain)) {}
+       sends_since_notify = 0;
 }
 
 /* Wait for all remaining completions on the errqueue */
@@ -549,6 +553,9 @@ static void do_tx(int domain, int type, int protocol)
                else
                        do_sendmsg(fd, &msg, cfg_zerocopy, domain);
 
+               if (cfg_zerocopy && sends_since_notify >= cfg_notification_limit)
+                       do_recv_completions(fd, domain);
+
                while (!do_poll(fd, POLLOUT)) {
                        if (cfg_zerocopy)
                                do_recv_completions(fd, domain);
@@ -708,7 +715,7 @@ static void parse_opts(int argc, char **argv)
 
        cfg_payload_len = max_payload_len;
 
-       while ((c = getopt(argc, argv, "46c:C:D:i:mp:rs:S:t:vz")) != -1) {
+       while ((c = getopt(argc, argv, "46c:C:D:i:l:mp:rs:S:t:vz")) != -1) {
                switch (c) {
                case '4':
                        if (cfg_family != PF_UNSPEC)
@@ -736,6 +743,9 @@ static void parse_opts(int argc, char **argv)
                        if (cfg_ifindex == 0)
                                error(1, errno, "invalid iface: %s", optarg);
                        break;
+               case 'l':
+                       cfg_notification_limit = strtoul(optarg, NULL, 0);
+                       break;
                case 'm':
                        cfg_cork_mixed = true;
                        break;