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[octeon]segment without execution priviledge,causing system down.

To: Linux MIPS Mailing List <linux-mips@linux-mips.org>
Subject: [octeon]segment without execution priviledge,causing system down.
From: "wilbur.chan" <wilbur512@gmail.com>
Date: Wed, 28 Apr 2010 09:29:27 +0800
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I'm using a modified kernel version derived from 2.6.21.7,and the cpu
is octeon cn5860. Strangely I found that , when executing

some instruction in  un-executable segment, the system will hang on,
together with console  down, and could not response to ping

command.

cn5860 has 16 CPUs,  in our system , each non-zero cpu is running a
real-time user-mode process with 99 priority(network

business) , causing non-zero cpus to 100% cpu-usage.

while cpu 0 ,is in charge of coordinating the whole system ,almost to
5~6% cpu-usage.



That is , the following code ,will cause a problem , which hang the
cpu 0, and then hang the whole system:

#include <stdio.h>
#include <stdlib.h>

char stack[8*1024] = {0}; // in un-executable segment
void (*func)(void);
int main()
{
        func = (void (*)(void))stack;  //convert to function  pointer
        func();    //cpu will hang
    return 0;
}

In my opinion, the code above should generate a page_fault exception ,
and caused SIGSEGV error, however in my

system , it hang on directly.


Any one knows why this happened? Thanks




regards,

wilbur

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