On Fri, Oct 16, 2020 at 12:44:33PM +0200, mwilck@xxxxxxxx wrote:
> From: Martin Wilck <mwilck@xxxxxxxx>
>
> The uxlsnr wouldn't always release the client lock when cancelled,
> causing a deadlock in uxsock_cleanup(). While this hasn't been
> caused by commit 3d611a2, the deadlock seems to have become much
> more likely after that patch. Solving this means that we have to
> treat reallocation failure of the pollfd array differently.
> We will now just ignore any clients above the last valid pfd index.
> That's a minor problem, as we're in an OOM situation anyway.
>
> Moreover, client_lock is not a "struct lock", but a plain
> pthread_mutex_t.
>
> Fixes: 3d611a2 ("multipathd: cancel threads early during shutdown")
Oops. Forgot to send this one.
Reviewed-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> ---
> multipathd/uxlsnr.c | 24 ++++++++++++++----------
> 1 file changed, 14 insertions(+), 10 deletions(-)
>
> diff --git a/multipathd/uxlsnr.c b/multipathd/uxlsnr.c
> index 1c5ce9d..ce2b680 100644
> --- a/multipathd/uxlsnr.c
> +++ b/multipathd/uxlsnr.c
> @@ -35,6 +35,7 @@
> #include "config.h"
> #include "mpath_cmd.h"
> #include "time-util.h"
> +#include "util.h"
>
> #include "main.h"
> #include "cli.h"
> @@ -116,7 +117,7 @@ static void _dead_client(struct client *c)
>
> static void dead_client(struct client *c)
> {
> - pthread_cleanup_push(cleanup_lock, &client_lock);
> + pthread_cleanup_push(cleanup_mutex, &client_lock);
> pthread_mutex_lock(&client_lock);
> _dead_client(c);
> pthread_cleanup_pop(1);
> @@ -302,10 +303,11 @@ void * uxsock_listen(uxsock_trigger_fn uxsock_trigger, long ux_sock,
> sigdelset(&mask, SIGUSR1);
> while (1) {
> struct client *c, *tmp;
> - int i, poll_count, num_clients;
> + int i, n_pfds, poll_count, num_clients;
>
> /* setup for a poll */
> pthread_mutex_lock(&client_lock);
> + pthread_cleanup_push(cleanup_mutex, &client_lock);
> num_clients = 0;
> list_for_each_entry(c, &clients, node) {
> num_clients++;
> @@ -322,14 +324,13 @@ void * uxsock_listen(uxsock_trigger_fn uxsock_trigger, long ux_sock,
> sizeof(struct pollfd));
> }
> if (!new) {
> - pthread_mutex_unlock(&client_lock);
> condlog(0, "%s: failed to realloc %d poll fds",
> "uxsock", 2 + num_clients);
> - sched_yield();
> - continue;
> + num_clients = old_clients;
> + } else {
> + old_clients = num_clients;
> + polls = new;
> }
> - old_clients = num_clients;
> - polls = new;
> }
> polls[0].fd = ux_sock;
> polls[0].events = POLLIN;
> @@ -347,11 +348,14 @@ void * uxsock_listen(uxsock_trigger_fn uxsock_trigger, long ux_sock,
> polls[i].fd = c->fd;
> polls[i].events = POLLIN;
> i++;
> + if (i >= 2 + num_clients)
> + break;
> }
> - pthread_mutex_unlock(&client_lock);
> + n_pfds = i;
> + pthread_cleanup_pop(1);
>
> /* most of our life is spent in this call */
> - poll_count = ppoll(polls, i, &sleep_time, &mask);
> + poll_count = ppoll(polls, n_pfds, &sleep_time, &mask);
>
> handle_signals(false);
> if (poll_count == -1) {
> @@ -384,7 +388,7 @@ void * uxsock_listen(uxsock_trigger_fn uxsock_trigger, long ux_sock,
> }
>
> /* see if a client wants to speak to us */
> - for (i = 2; i < num_clients + 2; i++) {
> + for (i = 2; i < n_pfds; i++) {
> if (polls[i].revents & POLLIN) {
> struct timespec start_time;
>
> --
> 2.28.0
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