Re: [RFC] kernel random segmentation fault?

[Hillf Danton]

> 
> Hi all:
> 
> I meet a kernel problem about the random segmentation fault(x86_64). In my testcase, the size of local variables exceeds 20MB.
> when run the testcase, it will cause segmentation fault(because the default stack size limit is 8192KB).
> when I increase the stack size limit to 1024000KB(ulimit -s 1024000), the testcase will pass.
> 
> But when I run the testcase 100 times, it will cause random segmentation fault.
> 
> Maybe the commit fee7e49d45149fba60156f5b59014f764d3e3728  "mm: propagate error from stack expansion even for guard page"
> cause this problems, when I revert it, the testcase will not cause random segmentation fault problem.
> 
> Can anyone give some ideas about this problem?
> 
> Best Regards
> Wang Long
> 
> ############ Test Environment #############
> 
> # uname -a
> Linux ivybridge 4.1.0-rc2+ #3 SMP PREEMPT Wed May 6 10:46:57 CST 2015 x86_64 x86_64 x86_64 GNU/Linux
> 
> 
> ############  The Testcase ################
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/resource.h>
> 
> #define KB *1024
> #define MB *(1024*1024)
> #define GB *(1024*1024*1024)
> 
> int main(int argc, char** argv)
> {
>     int ret;
>     struct rlimit rlim;
> 
>     rlim.rlim_cur=20 MB;
>     rlim.rlim_max=20 MB;

Can you please get rlimit before setting it?
And try again without reverting fee7e49d45?

>     ret = setrlimit(RLIMIT_AS, &rlim);
>     if ( 0 > ret)
>     {
>         perror("setrlimit failed");
>         exit(1);
>     }
> 
>     printf("setrlimit success\n");
> 
>     char tmp[20 MB];
>     int i = 0;
> 
>     for (i = 0; i < 20 MB; i++)
>     {
>         tmp[i]=1;
>     }
> 
>     printf("test success\n");
>     exit(1);
> }
> 

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