URL: https://github.com/SSSD/sssd/pull/785
Author: thalman
 Title: #785: Providers: Delay online check on startup
Action: opened

PR body:
"""
Typical usecase is system startup or network restart. In such
cases SSSD receives several messages from the system about
network change and immediately starts connecting.
With multiple addresses on interface or multiple interfaces
SSSD receives even more messages.

This patch introduces 1s delay for online check after first
message. It also limits number of checks to 3.
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/785/head:pr785
git checkout pr785
From d470df214b48dcba147a41bffc60fc4e379ae3bc Mon Sep 17 00:00:00 2001
From: Tomas Halman <thal...@redhat.com>
Date: Wed, 20 Mar 2019 15:44:02 +0100
Subject: [PATCH] Providers: Delay online check on startup

Typical usecase is system startup or network restart. In such
cases SSSD receives several messages from the system about
network change and immediately starts connecting.
With multiple addresses on interface or multiple interfaces
SSSD receives even more messages.

This patch introduces 1s delay for online check after first
message. It also limits number of checks to 3.
---
 src/providers/data_provider_be.c | 72 ++++++++++++++++++++++----------
 1 file changed, 49 insertions(+), 23 deletions(-)

diff --git a/src/providers/data_provider_be.c b/src/providers/data_provider_be.c
index 942952b24e..6d9969a5d8 100644
--- a/src/providers/data_provider_be.c
+++ b/src/providers/data_provider_be.c
@@ -74,7 +74,7 @@ bool be_is_offline(struct be_ctx *ctx)
     return ctx->offstat.offline;
 }
 
-static void check_if_online(struct be_ctx *be_ctx);
+static void check_if_online(struct be_ctx *be_ctx, int delay);
 
 static errno_t
 try_to_go_online(TALLOC_CTX *mem_ctx,
@@ -85,7 +85,7 @@ try_to_go_online(TALLOC_CTX *mem_ctx,
 {
     struct be_ctx *ctx = (struct be_ctx*) be_ctx_void;
 
-    check_if_online(ctx);
+    check_if_online(ctx, 0);
     return EOK;
 }
 
@@ -250,10 +250,36 @@ static errno_t be_check_online_request(struct be_ctx *be_ctx)
     return EOK;
 }
 
+static void check_if_online_delayed(struct tevent_context *ev, struct tevent_timer *tim,
+                                    struct timeval current_time, void *private_data)
+{
+    errno_t ret;
+    struct be_ctx *be_ctx = talloc_get_type(private_data, struct be_ctx);
+
+    be_run_unconditional_online_cb(be_ctx);
+
+    if (!be_is_offline(be_ctx)) {
+        DEBUG(SSSDBG_TRACE_INTERNAL,
+              "Backend is already online, nothing to do.\n");
+        return;
+    }
+
+    DEBUG(SSSDBG_TRACE_INTERNAL, "Trying to go back online!\n");
+
+    ret = be_check_online_request(be_ctx);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "Unable to create check online req.\n");
+    } else {
+        DEBUG(SSSDBG_OP_FAILURE, "Check online req created.\n");
+    }
+}
+
 static void be_check_online_done(struct tevent_req *req)
 {
     struct be_ctx *be_ctx;
     struct dp_reply_std *reply;
+    struct tevent_timer *time_event;
+    struct timeval schedule;
     errno_t ret;
 
     be_ctx = tevent_req_callback_data(req, struct be_ctx);
@@ -288,9 +314,11 @@ static void be_check_online_done(struct tevent_req *req)
     be_ctx->check_online_ref_count--;
 
     if (reply->dp_error != DP_ERR_OK && be_ctx->check_online_ref_count > 0) {
-        ret = be_check_online_request(be_ctx);
-        if (ret != EOK) {
-            DEBUG(SSSDBG_CRIT_FAILURE, "Unable to create check online req.\n");
+        schedule = tevent_timeval_current_ofs(0, 0);
+        time_event = tevent_add_timer(be_ctx->ev, be_ctx, schedule, check_if_online_delayed, be_ctx);
+
+        if (time_event == NULL) {
+            DEBUG(SSSDBG_OP_FAILURE, "Failed to schedule online check\n");
             goto done;
         }
         return;
@@ -306,28 +334,23 @@ static void be_check_online_done(struct tevent_req *req)
     }
 }
 
-static void check_if_online(struct be_ctx *be_ctx)
+static void check_if_online(struct be_ctx *be_ctx, int delay)
 {
-    errno_t ret;
-
-    be_run_unconditional_online_cb(be_ctx);
-
-    if (!be_is_offline(be_ctx)) {
-        DEBUG(SSSDBG_TRACE_INTERNAL,
-              "Backend is already online, nothing to do.\n");
-        return;
-    }
+    struct tevent_timer *time_event;
+    struct timeval schedule;
 
     /* Make sure nobody tries to go online while we are checking */
     be_ctx->offstat.went_offline = time(NULL);
 
-    DEBUG(SSSDBG_TRACE_INTERNAL, "Trying to go back online!\n");
-
     be_ctx->check_online_ref_count++;
 
     if (be_ctx->check_online_ref_count != 1) {
         DEBUG(SSSDBG_TRACE_INTERNAL,
               "There is an online check already running.\n");
+        /* Do not have more than 3 retries in the queue */
+        if (be_ctx->check_online_ref_count > 3) {
+            be_ctx->check_online_ref_count--;
+        }
         return;
     }
 
@@ -337,12 +360,15 @@ static void check_if_online(struct be_ctx *be_ctx)
         goto failed;
     }
 
-    ret = be_check_online_request(be_ctx);
-    if (ret != EOK) {
-        DEBUG(SSSDBG_CRIT_FAILURE, "Unable to create check online req.\n");
+    schedule = tevent_timeval_current_ofs(delay, 0);
+    time_event = tevent_add_timer(be_ctx->ev, be_ctx, schedule, check_if_online_delayed, be_ctx);
+
+    if (time_event == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "Scheduling check_if_online_delayed failed.\n");
         goto failed;
     }
 
+    DEBUG(SSSDBG_OP_FAILURE, "Schedule check_if_online_delayed in %ds.\n", delay);
     return;
 
 failed:
@@ -376,7 +402,7 @@ static void signal_be_reset_offline(struct tevent_context *ev,
                                     void *private_data)
 {
     struct be_ctx *ctx = talloc_get_type(private_data, struct be_ctx);
-    check_if_online(ctx);
+    check_if_online(ctx, 0);
 }
 
 static errno_t
@@ -708,7 +734,7 @@ data_provider_res_init(TALLOC_CTX *mem_ctx,
                        struct be_ctx *be_ctx)
 {
     resolv_reread_configuration(be_ctx->be_res->resolv);
-    check_if_online(be_ctx);
+    check_if_online(be_ctx, 0);
 
     return monitor_common_res_init(mem_ctx, sbus_req, NULL);
 }
@@ -728,7 +754,7 @@ data_provider_reset_offline(TALLOC_CTX *mem_ctx,
                             struct sbus_request *sbus_req,
                             struct be_ctx *be_ctx)
 {
-    check_if_online(be_ctx);
+    check_if_online(be_ctx, 1);
 
     return EOK;
 }
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