<h3>Description</h3>
<p>on busy servers, there's a sporadic crash in slow timer.<br>
we don't have any debugging data anymore nor a way to reliably reproduce it.<br>
just posting here in case someone sees the same and can find a way to reliably reproduce it and maybe test the patch below.</p>

<h3>Troubleshooting</h3>
<h4>Reproduction</h4>

<h3>Possible Solutions</h3>

<p>with the patch below we don't see any crashes<br>
either <code>tl</code> or <code>tl->f</code> is null when it crashes. this is probably some race condition</p>
<pre><code>diff --git a/src/core/timer.c b/src/core/timer.c
index 0e0dc8812..3c59db3da 100644
--- a/src/core/timer.c
+++ b/src/core/timer.c
@@ -1128,7 +1128,7 @@ void slow_timer_main()
 #endif
                                SET_RUNNING_SLOW(tl);
                                UNLOCK_SLOW_TIMER_LIST();
-                                       ret=tl->f(*ticks, tl, tl->data);
+                                       ret= (tl->f ? tl->f(*ticks, tl, tl->data) : 0);
                                        /* reset the configuration group handles */
                                        cfg_reset_all();
                                        if (ret==0){
</code></pre>
<h3>Additional Information</h3>
<ul>
<li><strong>Kamailio Version</strong> - output of <code>kamailio -v</code></li>
</ul>
<pre><code>5.1 / 5.2
</code></pre>
<ul>
<li><strong>Operating System</strong>:</li>
</ul>

<pre><code>CentOS7
</code></pre>

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