On Thu, Nov 18, 2021 at 11:58:22PM +0100, mwilck@xxxxxxxx wrote:
> From: Martin Wilck <mwilck@xxxxxxxx>
>
> The previous patches added the state machine and the timeout handling,
> but there was no wakeup mechanism for the uxlsnr for cases where
> client connections were waiting for the vecs lock.
>
> This patch uses the previously introduced wakeup mechanism of
> struct mutex_lock for this purpose. Processes which unlock the
> "global" vecs lock send an event in an eventfd which the uxlsnr
> loop is polling for.
>
> As we are now woken up for servicing client handlers that don't
> wait for input but for the lock, we need to set up the pollfds
> differently, and iterate over all clients when handling events,
> not only over the ones that are receiving. The hangup handling
> is changed, too. We have to look at every client, even if one has
> hung up. Note that I don't take client_lock for the loop in
> uxsock_listen(), it's not necessary and will be removed elsewhere
> in a follow-up patch.
>
> With this in place, the lock need not be taken in execute_handler()
> any more. The uxlsnr only ever calls trylock() on the vecs lock,
> avoiding any waiting for other threads to finish.
>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> ---
> multipathd/uxlsnr.c | 200 ++++++++++++++++++++++++++++----------------
> 1 file changed, 129 insertions(+), 71 deletions(-)
>
> diff --git a/multipathd/uxlsnr.c b/multipathd/uxlsnr.c
> index 87134d5..bf9780d 100644
> --- a/multipathd/uxlsnr.c
> +++ b/multipathd/uxlsnr.c
> @@ -24,6 +24,7 @@
> #include <signal.h>
> #include <stdbool.h>
> #include <sys/inotify.h>
> +#include <sys/eventfd.h>
> #include "checkers.h"
> #include "memory.h"
> #include "debug.h"
> @@ -70,6 +71,7 @@ struct client {
> enum {
> POLLFD_UX = 0,
> POLLFD_NOTIFY,
> + POLLFD_IDLE,
> POLLFDS_BASE,
> };
>
> @@ -90,6 +92,7 @@ static LIST_HEAD(clients);
> static pthread_mutex_t client_lock = PTHREAD_MUTEX_INITIALIZER;
> static struct pollfd *polls;
> static int notify_fd = -1;
> +static int idle_fd = -1;
> static char *watch_config_dir;
>
> static bool _socket_client_is_root(int fd)
> @@ -187,6 +190,17 @@ void uxsock_cleanup(void *arg)
> free_polls();
> }
>
> +void wakeup_cleanup(void *arg)
> +{
> + struct mutex_lock *lck = arg;
> + int fd = idle_fd;
> +
> + idle_fd = -1;
> + set_wakeup_fn(lck, NULL);
> + if (fd != -1)
> + close(fd);
> +}
> +
> struct watch_descriptors {
> int conf_wd;
> int dir_wd;
> @@ -293,6 +307,18 @@ static void handle_inotify(int fd, struct watch_descriptors *wds)
>
> static const struct timespec ts_zero = { .tv_sec = 0, };
>
> +/* call with clients lock held */
> +static bool __need_vecs_lock(void)
> +{
> + struct client *c;
> +
> + list_for_each_entry(c, &clients, node) {
> + if (c->state == CLT_WAIT_LOCK)
> + return true;
> + }
> + return false;
> +}
> +
> static int parse_cmd(struct client *c)
> {
> int r;
> @@ -310,40 +336,31 @@ static int parse_cmd(struct client *c)
> return r;
> }
>
> -static int execute_handler(struct client *c, struct vectors *vecs, int timeout)
> +static int execute_handler(struct client *c, struct vectors *vecs)
> {
> - int r;
> - struct timespec tmo;
>
> - if (!c->handler)
> + if (!c->handler || !c->handler->fn)
> return -EINVAL;
>
> - if (clock_gettime(CLOCK_REALTIME, &tmo) == 0) {
> - tmo.tv_sec += timeout;
> - } else {
> - tmo.tv_sec = 0;
> - }
> + return c->handler->fn(c->cmdvec, &c->reply, vecs);
> +}
>
> - if (c->handler->locked) {
> - int locked = 0;
> +static void wakeup_listener(void)
> +{
> + uint64_t one = 1;
>
> - pthread_cleanup_push(cleanup_lock, &vecs->lock);
> - if (tmo.tv_sec) {
> - r = timedlock(&vecs->lock, &tmo);
> - } else {
> - lock(&vecs->lock);
> - r = 0;
> - }
> - if (r == 0) {
> - locked = 1;
> - pthread_testcancel();
> - r = c->handler->fn(c->cmdvec, &c->reply, vecs);
> - }
> - pthread_cleanup_pop(locked);
> - } else
> - r = c->handler->fn(c->cmdvec, &c->reply, vecs);
> + if (idle_fd != -1 &&
> + write(idle_fd, &one, sizeof(one)) != sizeof(one))
> + condlog(1, "%s: failed", __func__);
> +}
>
> - return r;
> +static void drain_idle_fd(int fd)
> +{
> + uint64_t val;
> + int rc;
> +
> + rc = read(fd, &val, sizeof(val));
> + condlog(4, "%s: %d, %"PRIu64, __func__, rc, val);
> }
>
> void default_reply(struct client *c, int r)
> @@ -397,16 +414,19 @@ enum {
> STM_BREAK,
> };
>
> -static int client_state_machine(struct client *c, struct vectors *vecs)
> +static int client_state_machine(struct client *c, struct vectors *vecs,
> + short revents)
> {
> ssize_t n;
> const char *buf;
>
> - condlog(4, "%s: cli[%d] state=%d cmd=\"%s\" repl \"%s\"", __func__,
> - c->fd, c->state, c->cmd, get_strbuf_str(&c->reply));
> + condlog(4, "%s: cli[%d] poll=%x state=%d cmd=\"%s\" repl \"%s\"", __func__,
> + c->fd, revents, c->state, c->cmd, get_strbuf_str(&c->reply));
>
> switch (c->state) {
> case CLT_RECV:
> + if (!(revents & POLLIN))
> + return STM_BREAK;
> if (c->cmd_len == 0) {
> /*
> * We got POLLIN; assume that at least the length can
> @@ -462,17 +482,30 @@ static int client_state_machine(struct client *c, struct vectors *vecs)
> }
> if (c->error)
> set_client_state(c, CLT_SEND);
> + else if (c->handler->locked)
> + set_client_state(c, CLT_WAIT_LOCK);
> else
> set_client_state(c, CLT_WORK);
> return STM_CONT;
>
> case CLT_WAIT_LOCK:
It's not a big deal, but I would prefer a name like CLT_LOCKED_WORK
instead of CLT_WAIT_LOCK, to make it obvious that these are alternate
possibilites.
> - /* tbd */
> - set_client_state(c, CLT_WORK);
> - return STM_CONT;
> + if (trylock(&vecs->lock) == 0) {
> + /* don't use cleanup_lock(), lest we wakeup ourselves */
> + pthread_cleanup_push_cast(__unlock, &vecs->lock);
> + c->error = execute_handler(c, vecs);
> + pthread_cleanup_pop(1);
> + condlog(4, "%s: cli[%d] grabbed lock", __func__, c->fd);
> + free_keys(c->cmdvec);
> + c->cmdvec = NULL;
> + set_client_state(c, CLT_SEND);
> + return STM_CONT;
> + } else {
> + condlog(4, "%s: cli[%d] waiting for lock", __func__, c->fd);
> + return STM_BREAK;
> + }
>
> case CLT_WORK:
> - c->error = execute_handler(c, vecs, uxsock_timeout / 1000);
> + c->error = execute_handler(c, vecs);
> free_keys(c->cmdvec);
> c->cmdvec = NULL;
> set_client_state(c, CLT_SEND);
> @@ -499,9 +532,14 @@ static int client_state_machine(struct client *c, struct vectors *vecs)
> }
> }
>
> -static void handle_client(struct client *c, struct vectors *vecs)
> +static void handle_client(struct client *c, struct vectors *vecs, short revents)
> {
> - while (client_state_machine(c, vecs) == STM_CONT);
> + if (revents & (POLLHUP|POLLERR)) {
> + c->error = -ECONNRESET;
> + return;
> + }
> +
> + while (client_state_machine(c, vecs, revents) == STM_CONT);
> }
>
> /*
> @@ -514,6 +552,8 @@ void *uxsock_listen(long ux_sock, void *trigger_data)
> /* conf->sequence_nr will be 1 when uxsock_listen is first called */
> unsigned int sequence_nr = 0;
> struct watch_descriptors wds = { .conf_wd = -1, .dir_wd = -1 };
> + bool need_lock = false;
> + struct vectors *vecs = trigger_data;
>
> condlog(3, "uxsock: startup listener");
> polls = MALLOC(max_pfds * sizeof(*polls));
> @@ -524,6 +564,14 @@ void *uxsock_listen(long ux_sock, void *trigger_data)
> notify_fd = inotify_init1(IN_NONBLOCK);
> if (notify_fd == -1) /* it's fine if notifications fail */
> condlog(3, "failed to start up configuration notifications");
> +
> + pthread_cleanup_push(wakeup_cleanup, &vecs->lock);
> + idle_fd = eventfd(0, EFD_NONBLOCK|EFD_CLOEXEC);
> + if (idle_fd == -1)
> + condlog(1, "failed to create idle fd");
If the idle_fd doesn't get correctly set, that seems like a fatal error
to me.
> + else
> + set_wakeup_fn(&vecs->lock, wakeup_listener);
> +
> sigfillset(&mask);
> sigdelset(&mask, SIGINT);
> sigdelset(&mask, SIGTERM);
> @@ -575,16 +623,30 @@ void *uxsock_listen(long ux_sock, void *trigger_data)
> else
> polls[POLLFD_NOTIFY].events = POLLIN;
>
> + need_lock = __need_vecs_lock();
> + polls[POLLFD_IDLE].fd = idle_fd;
> + if (need_lock)
> + polls[POLLFD_IDLE].events = POLLIN;
> + else
> + polls[POLLFD_IDLE].events = 0;
> +
> /* setup the clients */
> - i = POLLFDS_BASE;
> - list_for_each_entry(c, &clients, node) {
> - polls[i].fd = c->fd;
> - polls[i].events = POLLIN;
> - i++;
> - if (i >= max_pfds)
> - break;
> - }
> - n_pfds = i;
> + i = POLLFDS_BASE;
> + list_for_each_entry(c, &clients, node) {
Nitpick: This would look clearer to me if, instead of a switch
statement, it was just
if (c->state != CLT_RECV)
continue;
polls[i].events = POLLIN;
polls[i].fd = c->fd;
...
-Ben
> + switch(c->state) {
> + case CLT_RECV:
> + polls[i].events = POLLIN;
> + break;
> + default:
> + /* don't poll for this client */
> + continue;
> + }
> + polls[i].fd = c->fd;
> + i++;
> + if (i >= max_pfds)
> + break;
> + }
> + n_pfds = i;
> pthread_cleanup_pop(1);
>
> /* most of our life is spent in this call */
> @@ -607,33 +669,28 @@ void *uxsock_listen(long ux_sock, void *trigger_data)
> handle_signals(true);
> continue;
> }
> + if (polls[POLLFD_IDLE].fd != -1 &&
> + polls[POLLFD_IDLE].revents & POLLIN)
> + drain_idle_fd(idle_fd);
>
> - /* see if a client wants to speak to us */
> - for (i = POLLFDS_BASE; i < n_pfds; i++) {
> - if (polls[i].revents & (POLLIN|POLLHUP|POLLERR)) {
> - c = NULL;
> - pthread_mutex_lock(&client_lock);
> - list_for_each_entry(tmp, &clients, node) {
> - if (tmp->fd == polls[i].fd) {
> - c = tmp;
> - break;
> - }
> - }
> - pthread_mutex_unlock(&client_lock);
> - if (!c) {
> - condlog(4, "cli%d: new fd %d",
> - i, polls[i].fd);
> - continue;
> - }
> - if (polls[i].revents & (POLLHUP|POLLERR)) {
> - condlog(4, "cli[%d]: Disconnected",
> - c->fd);
> - dead_client(c);
> - continue;
> - }
> - handle_client(c, trigger_data);
> - if (c->error == -ECONNRESET)
> - dead_client(c);
> + /* see if a client needs handling */
> + list_for_each_entry_safe(c, tmp, &clients, node) {
> + short revents = 0;
> +
> + for (i = POLLFDS_BASE; i < n_pfds; i++) {
> + if (polls[i].fd == c->fd) {
> + revents = polls[i].revents;
> + break;
> + }
> + }
> +
> + handle_client(c, trigger_data, revents);
> +
> + if (c->error == -ECONNRESET) {
> + condlog(4, "cli[%d]: disconnected", c->fd);
> + dead_client(c);
> + if (i < n_pfds)
> + polls[i].fd = -1;
> }
> }
> /* see if we got a non-fatal signal */
> @@ -649,5 +706,6 @@ void *uxsock_listen(long ux_sock, void *trigger_data)
> handle_inotify(notify_fd, &wds);
> }
>
> + pthread_cleanup_pop(1);
> return NULL;
> }
> --
> 2.33.1
--
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