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Date: Mon, 1 Jul 2024 14:51:24 -0700
From: Zijian Zhang <zijianzhang@...edance.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, netdev@...r.kernel.org
Cc: edumazet@...gle.com, cong.wang@...edance.com, xiaochun.lu@...edance.com
Subject: Re: [PATCH] selftests: fix OOM problem in msg_zerocopy selftest
On 7/1/24 2:22 PM, Willem de Bruijn wrote:
> zijianzhang@ wrote:
>> From: Zijian Zhang <zijianzhang@...edance.com>
>
>
> Remember to append to PATCH net or net-next in the subject line.
>
> Since the title has fix in it, I suppose this should go to net.
>
> As this is a test adjustment, I don't think it should go to stable.
> Still, fixes need a Fixes: tag. The below referenced commit is not the
> cause. Likely that sysctl could be set to a different value to trigger
> this on older kernels too.
>
> This has likely been present since the start of the test, so
>
> Fixes: 07b65c5b31ce ("test: add msg_zerocopy test")
>
My ignorance, thanks for pointing this out!
>> 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, because of the 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 core.sysctl_optmem_max.
>
> Regardless of how large you set this sysctl, right? It is suggested to
> increase it to at least 128KB.
>
Just retested, even though I set net.core.optmem_max to 128k+, the
problem still exists.
>> We introduce "cfg_notification_limit" to force sender to receive
>> notifications after some number of sendmsgs. And, notifications may not
>> come in order, because of the reason we present above.
>
> Which reason?
>
If I open the Lock debugging config, the notifications will be reordered.
>> We have order
>> checking code managed by cfg_verbose.
>>
>> Signed-off-by: Zijian Zhang <zijianzhang@...edance.com>
>> Signed-off-by: Xiaochun Lu <xiaochun.lu@...edance.com>
>> ---
>> tools/testing/selftests/net/msg_zerocopy.c | 14 ++++++++++++--
>> 1 file changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/testing/selftests/net/msg_zerocopy.c b/tools/testing/selftests/net/msg_zerocopy.c
>> index bdc03a2097e8..7ea5fb28c93d 100644
>> --- 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++;
>> @@ -435,7 +438,7 @@ static bool do_recv_completion(int fd, int domain)
>> /* Detect notification gaps. These should not happen often, if at all.
>> * Gaps can occur due to drops, reordering and retransmissions.
>> */
>> - if (lo != next_completion)
>> + if (cfg_verbose && lo != next_completion)
>> fprintf(stderr, "gap: %u..%u does not append to %u\n",
>> lo, hi, next_completion);
>> next_completion = hi + 1;
>> @@ -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;
>> --
>> 2.20.1
>>
>
>
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