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

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

[wilbur.chan]

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

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

[David Daney]

On 04/27/2010 06:29 PM, wilbur.chan wrote:
> 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.
>    
[...]
> Any one knows why this happened? Thanks
>    

I think I know.

There is a bug in your kernel.  Since execute inhibit support was not 
added to the upstream kernel until very recently, we must assume you got 
your kernel from some vendor.  You could either ask the vendor for a 
fix, or back port it yourself from:

http://www.linux-mips.org/git?p=linux.git;a=commitdiff;h=6dd9344cfc41bcc60a01cdc828cb278be7a10e01

David Daney