8220175: serviceability/dcmd/framework/VMVersionTest.java fails with a timeout

[Daniil Titov]

Thank you, Chris and Serguei, for reviewing this change.

I did more testing with a test program on Linux that repeats get_namespace_pid() method and reads from the real file ( the copy of /proc/<pid>/status).
I paused the program after the first several lines ( but not "NSpid:" line)  where processed and deleted all lines in the status file before " NSpid: ..." line in order 
to this line became the first in the edited file. After that the program continues in the while loop but it seems as the original file content was 
already buffered and the program just continues over the original unedited lines and successfully found the match.  

Best regards,
Daniil

On 6/19/19, 9:13 PM, "Chris Plummer" <chris.plummer at oracle.com> wrote:

    Hi Daniil,
    
    I think your fix is good, although I wonder about the robustness of this 
    function given that the status file can change while it is reading it. I 
    wonder if it can return a false negative because it never saw the 
    matching line. This could happen if a line gets deleted, causing the 
    matching line to suddenly be earlier in the file, possibly before the 
    current location being read. Anyway, that's not really related to the 
    current issue or fix, but if you think it might be an issue maybe a bug 
    should be filed for it.
    
    thanks,
    
    Chris
    
    On 6/19/19 9:02 PM, Daniil Titov wrote:
    > Please review the change that fixes an intermittent failure of serviceability/dcmd/framework/* tests on Linux platform.
    >
    > The problem here is that get_namespace_pid() method, that is called by mmap_attach_shared () that in turn is called by PerfMemory::attach(),
    > tries to read the namespace pid information from /proc/<pid>/status file. However, it doesn't check that the error indicator associated with
    > stream is set that results in the endless  loop (lines 664-677) if the process terminates after /proc/<pid>/status was opened (line 659)
    > and checked for null (line 661).
    >
    >    658	  snprintf(fname, sizeof(fname), "/proc/%d/status", vmid);
    >     659	  FILE *fp = fopen(fname, "r");
    >     660	
    >     661	  if (fp) {
    >     662	    int pid, nspid;
    >     663	    int ret;
    >     664	    while (!feof(fp)) {
    >     665	      ret = fscanf(fp, "NSpid: %d %d", &pid, &nspid);
    >     666	      if (ret == 1) {
    >     667	        break;
    >     668	      }
    >     669	      if (ret == 2) {
    >     670	        retpid = nspid;
    >     671	        break;
    >     672	      }
    >     673	      for (;;) {
    >     674	        int ch = fgetc(fp);
    >     675	        if (ch == EOF || ch == (int)'\n') break;
    >     676	      }
    >     677	    }
    >     678	    fclose(fp);
    >     679	  }
    >
    > The fix adds the check for the error indicator to ensure that the "while" loop terminates properly if the file no longer exists.
    >
    > Issues [3] and [4] have the same cause and will be closed as duplicates of this issue.
    >
    > Testing: Mach5 hotspot_serviceability tests succeeded, tier1,tier2, and tier3 tests are in progress.
    >
    > [1] Webrev: http://cr.openjdk.java.net/~dtitov/8220175/webrev.01/
    > [2] Bug: https://bugs.openjdk.java.net/browse/JDK-8220175
    > [3] https://bugs.openjdk.java.net/browse/JDK-8223600
    > [4] https://bugs.openjdk.java.net/browse/JDK-8217351
    >
    > Thanks!
    > -Daniil
    >
    >