Re: [Dmtcp-forum] popen/pclose bug

[Gene C. <ge...@cc...>]

Thanks very much for reporting this bug to us, along with a clear way
to reproduce it.  This should be a relatively simple bug for us to fix.
If you can wait a few weeks for the fix, that will be easiest for us
(see next paragraph).  But if you need a fix urgently, please tell us now.
    Kapil, I'll be travelling during this week, and classes start next week.
Is this the type of bug that your code reorganization for the 3.x branch
of DMTCP should fix?  Either way, could you write back to John Fredine
to let him know what to expect?

Thanks,
- Gene

On Mon, Aug 27, 2012 at 03:00:31PM +0000, Fredine, John wrote:
> Hi,
> 
> I have run into what appears to be a bug in the popen()/pclose() implementation in dmtcp 1.2.6.  It can be seen with a simple program like:
> 
>     #include <stdio.h>
>     #include <stdlib.h>
>     int main(int argc, char *argv)
>     {
>         FILE *f;
>         int   c;
> 
>        f = popen("ls -l", "r");
>         while ((c = fgetc(f)) != EOF) putchar(c);
>         pclose(f);
> 
>         f = popen("ls -l", "r");
>        while ((c = fgetc(f)) != EOF) putchar(c);
>         pclose(f);
>      }
> 
> In my case the second popen will fail with a "double free" error.  It looks like dmtcp is trying to track file handles opened by popen() and after spawning the child process, close any file handles in the child which were opened by previous popen calls.  The problem is that the pclose() function does not remove any file handles from the list of open file handles being tracked.  A subsequent call to popen() will cause a problem because it tries to close a file handle which is not open.  In my case a simple fix was to erase the file handle from _dmtcpPopenPidMap() in pclose().
> 
> Thanks,
> John Fredine

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