BUG/MEDIUM: proxy: protect "show servers ..." against backend deletion

This patch is a direct follow up of the previous one which fixes
commands "show servers conn/state". The current patch ensures that these
commands are safe even with task yielding and backend deletion in
parallel. This is also based on the watcher mechanism.

This must be backported up to 3.4.

diff --git a/src/proxy.c b/src/proxy.c
index 7839989396f3138201089bd915280554a4f150df..61457b49cfc7b63d4327190ba96a2e04796b4f23 100644 (file)
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -93,6 +93,7 @@ struct show_srv_ctx {
                SHOW_SRV_LIST,
        } state;
 
+       struct watcher px_watch;  /* watcher to automatically update px on backend deletion */
        struct watcher srv_watch; /* watcher to automatically update sv on server deletion */
 };
 
@@ -4440,6 +4441,8 @@ static int cli_parse_show_servers(char **args, char *payload, struct appctx *app
        struct proxy *px;
 
        ctx->show_conn = *args[2] == 'c'; // "conn" vs "state"
+
+       watcher_init(&ctx->px_watch,  &ctx->px, offsetof(struct proxy,  watcher_list));
        watcher_init(&ctx->srv_watch, &ctx->sv, offsetof(struct server, watcher_list));
 
        /* check if a backend name has been provided */
@@ -4450,7 +4453,7 @@ static int cli_parse_show_servers(char **args, char *payload, struct appctx *app
                if (!px)
                        return cli_err(appctx, "Can't find backend.\n");
 
-               ctx->px = px;
+               watcher_attach(&ctx->px_watch, px);
                ctx->only_pxid = px->uuid;
        }
        return 0;
@@ -4581,10 +4584,10 @@ static int cli_io_handler_servers_state(struct appctx *appctx)
                ctx->state = SHOW_SRV_LIST;
 
                if (!ctx->px)
-                       ctx->px = proxies_list;
+                       watcher_attach(&ctx->px_watch, proxies_list);
        }
 
-       for (; ctx->px != NULL; ctx->px = curproxy->next) {
+       for (; ctx->px; watcher_next(&ctx->px_watch, ctx->px->next)) {
                curproxy = ctx->px;
                /* servers are only in backends */
                if ((curproxy->cap & PR_CAP_BE) && !(curproxy->cap & PR_CAP_INT)) {
@@ -4592,8 +4595,10 @@ static int cli_io_handler_servers_state(struct appctx *appctx)
                                return 0;
                }
                /* only the selected proxy is dumped */
-               if (ctx->only_pxid)
+               if (ctx->only_pxid) {
+                       watcher_detach(&ctx->px_watch);
                        break;
+               }
        }
 
        return 1;