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List:       oprofile-list
Subject:    [ oprofile-Bugs-3610048 ] operf can't profile a process that changed its name.
From:       SourceForge.net <noreply () sourceforge ! net>
Date:       2013-04-09 22:28:47
Message-ID: E1UPh22-0000YN-V3 () sfs-ml-4 ! v29 ! ch3 ! sourceforge ! com
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Bugs item #3610048, was opened at 2013-04-04 18:30
Message generated for change (Comment added) made by gh4ck3r
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=116191&aid=3610048&group_id=16191

Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request,
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Ghacker (gh4ck3r)
Assigned to: Maynard Johnson (maynardj)
Summary: operf can't profile a process that changed its name.

Initial Comment:
I make a sample and patch for this.
Please refer to https://github.com/ChangbinPark/Oprofile/issues/1 for more detailed information

----------------------------------------------------------------------

>Comment By: Ghacker (gh4ck3r)
Date: 2013-04-09 15:28

Message:
I totally understand the case that is not considered.
And I'm glad to hear you already have a patch for it.
I hope it works fine with the specjbb and mine.

Please let me know whenever your patch is ready to be tested.
Thanks for your effort.

----------------------------------------------------------------------

Comment By: Maynard Johnson (maynardj)
Date: 2013-04-09 14:06

Message:
Thanks for the testcase to reproduce the problem, and for the patch to fix
it.  The fix, though, isn't quite complete.  If the target program that
does prctl() ends before operf gets around to processing its samples and
other data we get from the kernel, then the readlink will fail, so we need
to be able to handle that.

Coincidentally, I've been working on an operf bug that involves the same
area of code that your patch changes (i.e., obtaining an appropriate
appname for a process).  The bug was reported by a user running specjbb
with Java 7, which has lots of threads created via fork/exec by the main
JVM process.  While coding the fix for this, I employed your readlink
technique as a first attempt for trying to obtain the appname since it's
faster than using the PERF_RECORD_COMM and PERF_RECORD_MMAP data from the
kernel.  But my code also handles the case where readlink fails due to the
process having ended, and it falls back to the technique of comparing the
'comm' data (app shortname) with the filename segment of mmap'ed pathnames.
 I also made a change so that if a program does a prctl() to change the
name to "foo" and then the program ends before operf can do a readlink for
it, we will default to attributing the samples to "foo".  So samples won't
get dropped, no matter what.

The specjbb user who reported the aforementioned problem is testing my
patch now.  If all goes well, I'll be posting it to the list soon.  So,
just to be clear, that patch will fix also the problem you reported here,
so I'll come back and ask you to test it.  Thanks.

----------------------------------------------------------------------

Comment By: https://www.google.com/accounts ()
Date: 2013-04-07 19:33

Message:
Here's my description.

A process that changed it's name via "prctl" system call can't be profiled
with oprofile at all.

Sample code)
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/prctl.h>

int main(int argc, char *argv[])
{
    char name[BUFSIZ]={0,};
    unsigned long i=0;
    if(argc>1) prctl(PR_SET_NAME, (unsigned long)argv[1], 0, 0);
    prctl(PR_GET_NAME, name, 0, 0);
    while(1){
        printf("My name is %s and pid %d. I'm busy....[%ld]\n" , name,
getpid(), ++i);
        sleep(1);
    }
    return 0;
}

If above program is executed with a parameter other than its executable
name, it can't be profiled with Oprofile.

----------------------------------------------------------------------

Comment By: Maynard Johnson (maynardj)
Date: 2013-04-05 08:20

Message:
Thanks for your bug report.  Please add a full description of the problem
here in this bug report, and attach your patch here (following patch
contribution guidelines documented at
http://oprofile.sourceforge.net/contribute/).  Thanks!

----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=116191&aid=3610048&group_id=16191

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