Message-ID: <sjvtcbqkewl6n2sh4eukwhj2grcun5outspl2chm3dmlomxgxh@sycexvmnhsn3>
Date: Tue, 15 Oct 2024 20:32:50 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Anjali Kulkarni <anjali.k.kulkarni@...cle.com>
Cc: "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
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        "mingo@...hat.com" <mingo@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "dietmar.eggemann@....com" <dietmar.eggemann@....com>,
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        "vschneid@...hat.com" <vschneid@...hat.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        Pei Li <peili.io@...cle.com>
Subject: Re: [PATCH net-next v2 3/3] connector/cn_proc: Selftest for threads

* Anjali Kulkarni <anjali.k.kulkarni@...cle.com> [241015 17:28]:
> 
> 
> > On Oct 15, 2024, at 12:27 PM, Liam Howlett <liam.howlett@...cle.com> wrote:
> > 
> > * Anjali Kulkarni <anjali.k.kulkarni@...cle.com> [241015 13:30]:
> >> Test to check if setting PROC_CN_MCAST_NOTIFY in proc connector API, allows
> >> a thread's non-zero exit status to be returned to proc_filter.
> >> 
> >> The threads.c program creates 2 child threads. 1st thread handles signal
> >> SIGSEGV, and 2nd thread needs to indicate some error condition (value 1)
> >> to the kernel, instead of using pthread_exit() with 1.
> >> 
> >> In both cases, child sends notify_netlink_thread_exit(exit_code) to kernel,
> >> to let kernel know it has exited abnormally with exit_code.
> >> 
> >> Compile:
> >>    make thread
> >>    make proc_filter
> >> To see non-zero exit notifications, run:
> >>    ./proc_filter -f
> >> Run threads code in another window:
> >>    ./threads
> >> Note the 2 child thread IDs reported above
> >> Send SIGSEGV signal to the child handling SIGSEGV:
> >>    kill -11 <child1-tid>
> >> Watch the child 1 tid being notified with exit code 11 to proc_filter
> >> Watch child 2 tid being notified with exit code 1 (value defined in code)
> >> to proc_filter
> >> 
> >> Signed-off-by: Anjali Kulkarni <anjali.k.kulkarni@...cle.com>
> >> ---
> >> tools/testing/selftests/connector/Makefile    |  23 +++-
> >> .../testing/selftests/connector/proc_filter.c |   5 +
> >> tools/testing/selftests/connector/thread.c    | 116 ++++++++++++++++++
> >> .../selftests/connector/thread_filter.c       |  96 +++++++++++++++
> >> 4 files changed, 239 insertions(+), 1 deletion(-)
> >> create mode 100644 tools/testing/selftests/connector/thread.c
> >> create mode 100644 tools/testing/selftests/connector/thread_filter.c
> >> 
> >> diff --git a/tools/testing/selftests/connector/Makefile b/tools/testing/selftests/connector/Makefile
> >> index 92188b9bac5c..bf335826bc3b 100644
> >> --- a/tools/testing/selftests/connector/Makefile
> >> +++ b/tools/testing/selftests/connector/Makefile
> >> @@ -1,5 +1,26 @@
> >> # SPDX-License-Identifier: GPL-2.0
> >> -CFLAGS += -Wall $(KHDR_INCLUDES)
> >> +KERNEL="../../../.."
> >> +
> >> +CFLAGS += -Wall $(KHDR_INCLUDES) -I $(KERNEL)/include/uapi -I $(KERNEL)/include
> >> +
> >> +proc_filter: proc_filter.o
> >> + cc proc_filter.o -o proc_filter
> >> +
> >> +proc_filter.o: proc_filter.c
> >> + cc -c proc_filter.c -o proc_filter.o $(CFLAGS)
> >> +
> >> +thread: thread.o thread_filter.o
> >> + cc thread.o thread_filter.o -o thread
> >> +
> >> +thread.o: thread.c $(DEPS)
> >> + cc -c thread.c -o thread.o $(CFLAGS)
> >> +
> >> +thread_filter.o: thread_filter.c
> >> + cc -c thread_filter.c -o thread_filter.o $(CFLAGS)
> >> +
> >> +define EXTRA_CLEAN
> >> + rm *.o thread
> >> +endef
> >> 
> >> TEST_GEN_PROGS = proc_filter
> >> 
> >> diff --git a/tools/testing/selftests/connector/proc_filter.c b/tools/testing/selftests/connector/proc_filter.c
> >> index 4a825b997666..6fb4842894f8 100644
> >> --- a/tools/testing/selftests/connector/proc_filter.c
> >> +++ b/tools/testing/selftests/connector/proc_filter.c
> >> @@ -1,4 +1,9 @@
> >> // SPDX-License-Identifier: GPL-2.0-only
> >> +/*
> >> + * Author: Anjali Kulkarni <anjali.k.kulkarni@...cle.com>
> >> + *
> >> + * Copyright (c) 2024 Oracle and/or its affiliates.
> >> + */
> >> 
> >> #include <sys/types.h>
> >> #include <sys/epoll.h>
> >> diff --git a/tools/testing/selftests/connector/thread.c b/tools/testing/selftests/connector/thread.c
> >> new file mode 100644
> >> index 000000000000..8c9abf6115d6
> >> --- /dev/null
> >> +++ b/tools/testing/selftests/connector/thread.c
> >> @@ -0,0 +1,116 @@
> >> +// SPDX-License-Identifier: GPL-2.0-only
> >> +/*
> >> + * Author: Anjali Kulkarni <anjali.k.kulkarni@...cle.com>
> >> + *
> >> + * Copyright (c) 2024 Oracle and/or its affiliates.
> >> + */
> >> +
> >> +#include <pthread.h>
> >> +#include <stdio.h>
> >> +#include <unistd.h>
> >> +#include <stdlib.h>
> >> +#include <signal.h>
> >> +
> >> +/*
> >> + * This code tests a thread exit notification when thread exits abnormally.
> >> + * Normally, when a thread exits abnormally, the kernel is not aware of the
> >> + * exit code. This is usually only conveyed from child to parent via the
> >> + * pthread_exit() and pthread_join() calls. Sometimes, however, a parent
> >> + * process cannot monitor all child processes via pthread_join(), particularly
> >> + * when there is a huge amount of child processes. In this case, the parent
> >> + * has created the child with PTHREAD_CREATE_DETACHED attribute.
> >> + * To fix this problem, either when child wants to convey non-zero exit via
> >> + * pthread_exit() or in a signal handler, the child can notify the kernel's
> >> + * connector module it's exit status via a netlink call with new type
> >> + * PROC_CN_MCAST_NOTIFY. (Implemented in the thread_filter.c file).
> >> + * This will send the exit code from the child to the kernel, which the kernel
> >> + * can later return to proc_filter program when the child actually exits.
> >> + * To test this usecase:
> >> + * Compile:
> >> + * make thread
> >> + * make proc_filter
> >> + * To see non-zero exit notifications, run:
> >> + * ./proc_filter -f
> >> + * Start the threads code, creating 2 threads, in another window:
> >> + * ./threads
> >> + * Note the 2 child thread IDs reported above
> >> + * Send SIGSEGV signal to the child handling SIGSEGV:
> >> + * kill -11 <child1-tid>
> >> + * Watch the event being notified with exit code 11 to proc_filter
> >> + * Watch child 2 tid being notified with exit code 1 (value defined in code)
> >> + * to proc_filter
> >> + */
> >> +
> >> +extern int notify_netlink_thread_exit(unsigned int exit_code);
> >> +
> >> +static void sigsegvh(int sig)
> >> +{
> >> + unsigned int exit_code = (unsigned int) sig;
> >> + /*
> >> +  * Send any non-zero value to get a notification. Here we are
> >> +  * sending the signal number for SIGSEGV which is 11
> >> +  */
> >> + notify_netlink_thread_exit(exit_code);
> >> +}
> >> +
> >> +void *threadc1(void *ptr)
> >> +{
> >> + signal(SIGSEGV, sigsegvh);
> >> + printf("Child 1 thread id %d, handling SIGSEGV\n", gettid());
> >> + sleep(20);
> >> + pthread_exit(NULL);
> >> +}
> >> +
> >> +void *threadc2(void *ptr)
> >> +{
> >> + int exit_val = 1;
> >> +
> >> + printf("Child 2 thread id %d, wants to exit with value %d\n",
> >> + gettid(), exit_val);
> >> + sleep(2);
> >> + notify_netlink_thread_exit(exit_val);
> >> + pthread_exit(NULL);
> >> +}
> >> +
> >> +int main(int argc, char **argv)
> >> +{
> >> + pthread_t thread1, thread2;
> >> + pthread_attr_t attr1, attr2;
> >> + int ret;
> >> +
> >> + ret = pthread_attr_init(&attr1);
> >> + if (ret != 0) {
> >> + perror("pthread_attr_init failed");
> >> + exit(ret);
> >> + }
> >> + ret = pthread_attr_setdetachstate(&attr1, PTHREAD_CREATE_DETACHED);
> >> + if (ret != 0) {
> >> + perror("pthread_attr_setdetachstate failed");
> >> + exit(ret);
> >> + }
> >> + ret = pthread_create(&thread1, &attr1, *threadc1, NULL);
> >> + if (ret != 0) {
> >> + perror("pthread_create failed");
> >> + exit(ret);
> >> + }
> >> +
> >> + ret = pthread_attr_init(&attr2);
> >> + if (ret != 0) {
> >> + perror("pthread_attr_init failed");
> >> + exit(ret);
> >> + }
> >> + ret = pthread_attr_setdetachstate(&attr2, PTHREAD_CREATE_DETACHED);
> >> + if (ret != 0) {
> >> + perror("pthread_attr_setdetachstate failed");
> >> + exit(ret);
> >> + }
> >> + ret = pthread_create(&thread2, &attr2, *threadc2, NULL);
> >> + if (ret != 0) {
> >> + perror("pthread_create failed");
> >> + exit(ret);
> >> + }
> > 
> > I expected the test to check for the correct value to be returned?
> > Could you use pthread_join() and verify the same value is returned
> > through the new mechanism, or will they not match?
> 
> This is a manual test, you need to check visually that the proc_filter
> Is returning correct values for the 2 cases. I can make this an
> automated test, reading the output of proc_filter directly from a file
> and checking the values are as expected.
> There is also another test program which does an automated test
> of the values returned by proc_filter for scale (100k or so), which I
> will send out later. (The co-author of that patch, who wrote the
> original code for processes, is away - @peili.io@...cle.com)
> pthread_join() cannot return a value to the kernel, so we cannot
> use it to verify the new mechanism. 


Okay, as long as there is an automatic test then it's probably fine.

> 
> > 
> >> +
> >> + /* Wait for children to exit or be killed */
> >> + sleep(30);
> >> + exit(0);
> >> +}
> >> diff --git a/tools/testing/selftests/connector/thread_filter.c b/tools/testing/selftests/connector/thread_filter.c
> >> new file mode 100644
> >> index 000000000000..3da740aa7537
> >> --- /dev/null
> >> +++ b/tools/testing/selftests/connector/thread_filter.c
> >> @@ -0,0 +1,96 @@
> >> +// SPDX-License-Identifier: GPL-2.0-only
> >> +/*
> >> + * Author: Anjali Kulkarni <anjali.k.kulkarni@...cle.com>
> >> + *
> >> + * Copyright (c) 2024 Oracle and/or its affiliates.
> >> + */
> >> +
> >> +#include <sys/types.h>
> >> +#include <sys/epoll.h>
> >> +#include <sys/socket.h>
> >> +#include <linux/netlink.h>
> >> +#include <linux/connector.h>
> >> +#include <linux/cn_proc.h>
> >> +
> >> +#include <stddef.h>
> >> +#include <stdio.h>
> >> +#include <stdlib.h>
> >> +#include <unistd.h>
> >> +#include <strings.h>
> >> +#include <errno.h>
> >> +#include <signal.h>
> >> +#include <string.h>
> >> +
> >> +#define NL_MESSAGE_SIZE (sizeof(struct nlmsghdr) + sizeof(struct cn_msg) + \
> >> + sizeof(struct proc_input))
> >> +
> >> +/*
> >> + * Send PROC_CN_MCAST_NOTIFY type notification to the connector code in kernel.
> >> + * This will send the exit_code specified by user to the connector layer, so
> >> + * it can send a notification for that event to any listening process
> >> + */
> >> +int send_message(int nl_sock, unsigned int exit_code)
> >> +{
> >> + char buff[NL_MESSAGE_SIZE];
> >> + struct nlmsghdr *hdr;
> >> + struct cn_msg *msg;
> >> +
> >> + hdr = (struct nlmsghdr *)buff;
> >> + hdr->nlmsg_len = NL_MESSAGE_SIZE;
> >> + hdr->nlmsg_type = NLMSG_DONE;
> >> + hdr->nlmsg_flags = 0;
> >> + hdr->nlmsg_seq = 0;
> >> + hdr->nlmsg_pid = getpid();
> >> +
> >> + msg = (struct cn_msg *)NLMSG_DATA(hdr);
> >> + msg->id.idx = CN_IDX_PROC;
> >> + msg->id.val = CN_VAL_PROC;
> >> + msg->seq = 0;
> >> + msg->ack = 0;
> >> + msg->flags = 0;
> >> +
> >> + msg->len = sizeof(struct proc_input);
> >> + ((struct proc_input *)msg->data)->mcast_op =
> >> + PROC_CN_MCAST_NOTIFY;
> >> + ((struct proc_input *)msg->data)->uexit_code = exit_code;
> >> +
> >> + if (send(nl_sock, hdr, hdr->nlmsg_len, 0) == -1) {
> >> + perror("send failed");
> >> + return -errno;
> >> + }
> >> + return 0;
> >> +}
> >> +
> >> +int notify_netlink_thread_exit(unsigned int exit_code)
> >> +{
> >> + struct sockaddr_nl sa_nl;
> >> + int err = 0;
> >> + int nl_sock;
> >> +
> >> + nl_sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
> >> +
> >> + if (nl_sock == -1) {
> >> + perror("socket failed");
> >> + return -errno;
> >> + }
> >> +
> >> + bzero(&sa_nl, sizeof(sa_nl));
> >> + sa_nl.nl_family = AF_NETLINK;
> >> + sa_nl.nl_groups = CN_IDX_PROC;
> >> + sa_nl.nl_pid    = gettid();
> >> +
> >> + if (bind(nl_sock, (struct sockaddr *)&sa_nl, sizeof(sa_nl)) == -1) {
> >> + perror("bind failed");
> >> + close(nl_sock);
> >> + return -errno;
> >> + }
> >> +
> >> + err = send_message(nl_sock, exit_code);
> >> +
> >> + close(nl_sock);
> >> +
> >> + if (err < 0)
> >> + return err;
> >> +
> >> + return 0;
> >> +}
> >> -- 
> >> 2.46.0
> 
> 

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