502 & 504 error, again

[Geoge.Q]

I know it should be a well-known issue.
I searched and try to find out what on earth it is, but I failed.

Step:
1) nginx works as reverse proxy and the version is V1.0.5,
   OS: Debian 5.0.3, Kernel Version 2.6.32

2) Enabled http 1.1,   504 error  is popup in client;
the error log indicates:
-------------------------------------------------
2011/12/30 09:40:06 [error] 11013#0: *1 upstream timed out (110: Connection
timed out) while reading response header from upstream, client:
10.208.127.142, server: 1.1.1.1, request: "POST
/QueryStatManage/StatStudentAction.aspx HTTP/1.1", upstream: "
http://1.1.1.1:80/QueryStatManage/StatStudentAction.aspx", host: "1.1.1.1",
referrer: "http://1.1.1.1/QueryStatManage/StatStudentAction.aspx"
-------------------------------------------------


3) increase the vaule
     > proxy_read_timeout 600s
     > proxy_send_timeout 600s

   this time, it is poped up 502, the error logs indicates
------------------------------------
2011/12/30 09:53:54 [error] 11173#0: *1 upstream prematurely closed
connection while reading response header from upstream, client:
10.208.127.142, server: 1.1.1.1, request: "POST
/QueryStatManage/StatStudentAction.aspx HTTP/1.1", upstream: "
http://1.1.1.1:80/QueryStatManage/StatStudentAction.aspx", host: "1.1.1.1",
referrer: "http://1.1.1.1/QueryStatManage/StatStudentAction.aspx"

4) Someone told me that there is a kernel bug in linux, I am not sure, can
someone see the same issue ?


thanks
George
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