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Re: [PATCH 2/2] Prevent vhost-user-blk-test hang
From: |
address@hidden |
Subject: |
Re: [PATCH 2/2] Prevent vhost-user-blk-test hang |
Date: |
Fri, 27 Aug 2021 13:55:41 -0500 |
User-agent: |
NeoMutt/20210205-739-420e15 |
On Fri, Aug 27, 2021 at 04:50:47PM +0000, Raphael Norwitz wrote:
> In the vhost-user-blk-test, as of now there is nothing stoping
stopping
> vhost-user-blk in QEMU writing to the socket right after forking off the
> storage daemon before it has a chance to come up properly, leaving the
> test hanging forever. This intermittently hanging test has caused QEMU
> automation failures reported multiple times on the mailing list [1].
>
> This change makes the storage-daemon notify the vhost-user-blk-test
> that it is fully initialized and ready to handle client connections via
> a pipefd before allowing the test to proceed. This ensures that the
> storage-daemon backend won't miss vhost-user messages and thereby
> resolves the hang.
As I said on patch 1, I think the proper fix here is to utilize the
--pidfile option.
>
> [1]
> https://lore.kernel.org/qemu-devel/CAFEAcA8kYpz9LiPNxnWJAPSjc=nv532bEdyfynaBeMeohqBp3A@mail.gmail.com/
>
> Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> ---
> tests/qtest/vhost-user-blk-test.c | 33 ++++++++++++++++++++++++++++---
> 1 file changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/tests/qtest/vhost-user-blk-test.c
> b/tests/qtest/vhost-user-blk-test.c
> index 6f108a1b62..b62af449df 100644
> --- a/tests/qtest/vhost-user-blk-test.c
> +++ b/tests/qtest/vhost-user-blk-test.c
> @@ -21,6 +21,8 @@
> #include "libqos/vhost-user-blk.h"
> #include "libqos/libqos-pc.h"
>
> +const char *daemon_msg = "Block exports setup\n";
> +
> #define TEST_IMAGE_SIZE (64 * 1024 * 1024)
> #define QVIRTIO_BLK_TIMEOUT_US (30 * 1000 * 1000)
> #define PCI_SLOT_HP 0x06
> @@ -885,7 +887,8 @@ static void start_vhost_user_blk(GString *cmd_line, int
> vus_instances,
> int num_queues)
> {
> const char *vhost_user_blk_bin = qtest_qemu_storage_daemon_binary();
> - int i;
> + int i, err, pipe_fds[2];
> + char buf[32] = {0};
> gchar *img_path;
> GString *storage_daemon_command = g_string_new(NULL);
> QemuStorageDaemonState *qsd;
> @@ -898,6 +901,12 @@ static void start_vhost_user_blk(GString *cmd_line, int
> vus_instances,
> " -object memory-backend-memfd,id=mem,size=256M,share=on "
> " -M memory-backend=mem -m 256M ");
>
> + err = pipe(pipe_fds);
> + if (err != 0) {
> + fprintf(stderr, "start_vhost_user_blk: pipe() failed %m\n");
> + abort();
> + }
Instead of setting up a pipe()...
> +
> for (i = 0; i < vus_instances; i++) {
> int fd;
> char *sock_path = create_listen_socket(&fd);
> @@ -914,22 +923,40 @@ static void start_vhost_user_blk(GString *cmd_line, int
> vus_instances,
> i + 1, sock_path);
> }
>
> + g_string_append_printf(storage_daemon_command, "--printset");
...change this to request the --pidfile option...
> +
> g_test_message("starting vhost-user backend: %s",
> storage_daemon_command->str);
> +
> pid_t pid = fork();
> if (pid == 0) {
> + close(pipe_fds[0]);
> +
> /*
> * Close standard file descriptors so tap-driver.pl pipe detects when
> * our parent terminates.
> */
> close(0);
> - close(1);
> open("/dev/null", O_RDONLY);
> - open("/dev/null", O_WRONLY);
> + close(1);
> + dup2(pipe_fds[1], 1);
>
> execlp("/bin/sh", "sh", "-c", storage_daemon_command->str, NULL);
> exit(1);
> }
> +
> + close(pipe_fds[1]);
> +
> + err = read(pipe_fds[0], buf, 20);
> + if (err < 0) {
> + fprintf(stderr, "Failed to read from storage-daemon pipe %m\n");
> + abort();
> + } else if (strcmp(buf, daemon_msg) != 0) {
> + fprintf(stderr, "qemu-storage-daemon did not write expected messaage
> "
> + "to the pipe. Total bytes read: %d. Got: %s\n", err, buf);
> + abort();
> + }
...and instead of trying to read() from a pipe, you instead wait until
the pid file exists.
> +
> g_string_free(storage_daemon_command, true);
>
> qsd = g_new(QemuStorageDaemonState, 1);
> --
> 2.20.1
>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org