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POTCP Socket hanging - both sides stuck in sendto()
 

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  1. POTCP Socket hanging - both sides stuck in sendto()
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    <p>We have an linux application (we don't have the source) that seems to be hanging. The socket between the two processes is reported as ESTABLISHED, and there is some data in the kernel socket buffer (although nowhere near the configured 16M via wmem/rmem). Both ends of the socket seem to be stuck on a sendto().</p> <p>Below is some investigation using netstat/lsof and strace:</p> <h2>HOST A (10.152.20.28)</h2> <pre><code>[root@hosta ~]# lsof -n -u df01 | grep 12959 | grep 12u q 12959 df01 12u IPv4 4398449 TCP 10.152.20.28:38521-&gt;10.152.20.29:gsigatekeeper (ESTABLISHED) [root@hosta ~]# netstat -anp | grep 38521 tcp 268754 90712 10.152.20.28:38521 10.152.20.29:2119 ESTABLISHED 12959/q [root@hosta ~]# strace -p 12959 Process 12959 attached - interrupt to quit sendto(12, "sometext\0somecode\0More\0exJKsss"..., 542, 0, NULL, 0 &lt;unfinished ...&gt; Process 12959 detached [root@hosta~]# </code></pre> <h2>HOST B (10.152.20.29)</h2> <pre><code>[root@hostb ~]# netstat -anp | grep 38521 tcp 72858 110472 10.152.20.29:2119 10.152.20.28:38521 ESTABLISHED 25512/q [root@hostb ~]# lsof -n -u df01 | grep 38521 q 25512 df01 14u IPv4 6456715 TCP 10.152.20.29:gsigatekeeper-&gt;10.152.20.28:38521 (ESTABLISHED) [root@hostb ~]# strace -p 25512 Process 25512 attached - interrupt to quit sendto(14, "\0\10\0\0\0Owner\0sym\0Type\0Ctpy\0Time\0Lo"..., 207, 0, NULL, 0 &lt;unfinished ...&gt; Process 25512 detached [root@hostb~]# </code></pre> <p>We have upgraded the NIC driver to the latest and greatest. The systems are running RHEL 5.6 x64 (2.6.18-238.el5), I have checked the eratta for RHEL 5.7 and 5.8 but I can see no mention of bugs with the bnx2 driver or the kernel.</p> <p>Does anyone have any ideas of how to debug this further?</p>
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    1. USThe_Viper
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    1. COYour system is fine, but your application is broken. Trash it. The programmer is most likely doing synchronous I/O in an unsafe way, leading to this deadlock.
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    2. COgenerally the available space is half of the configured wmem/rmem, often less.
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