Bug 2839

At least simple java programs work fine for me on 2.6 with the 32bit 1.4.2 JDK
from Sun. Does a java hello world also crash for you?

I have no time to debug tomcat sorry, someone who knows more about it 
has to do that. Have you contacted Sun or the tomcat maintainers about it?

This is information that we received from Sun in regards to this problem:

Here is comment from our HotsSpot engineer:

  That's a kernel issue. They should not log SEGSEGV if the signal
  is handled by user application. JVM uses SIGSEGV and several
  other signals (e.g. for implicit null check, safepoint polling, etc.)
  What is the OS version? Redhat used to have this problem in one of
  their beta release, we talked to them and it's fixed in FCS. Someone
  should log a bug with the Linux vendor.

  As to performance, yes, excessive logging could have a performance
  impact, because it is disk I/O. But usually the segfault happens
  infrequently so the impact is negligible and it's mainly a cosmetic
  thing. Depending on the number of threads, if they get hundreds of
  segfaults in a second, that could imply a problem in the Java app
  (e.g. deref null pointer in inner loop) or in JVM.

I have passed your OS information to them. Keep you posted if
I get any more information.

Regards,
-- 
Ingrid Yao
CAP program Developer Support Engineer
Java Web Service
Sun Microsystems

The Sun analysis is outdated. Current kernels log the signal
only when the signal is not handled by sigaction and no debugger is running.
This basically only happens when the program is really crashing,
it's extremly unlikely to be not a crash.

I do believe that the app (the java JVM) _is_ really crashing because my webapps
(running in the tomcat container) do not run correctly at all and I did manage
to get 1.5.0-beta1 to dump a core file.

However, the point is that the JVM's do not crash under 2.4.27-rc5 X86_64. I am
not alledging that the kernel is too blame instead of java, it may be either
one. Perhaps there is a bug in the JVM that it can get away with in 2.4.x. I was
just hoping that someone might have some clues. Either way this is a problem for
myself and others uses who want to develop Java apps. on the x86_64 platform.

Once again, the application is dying with SIGABORT. don't know if that is
significant or not. I am willing to help get to the bottom of this, just looking
for pointers.

OS is Fedora Core 2 X86_64.

Created attachment 3138 [details]
Fix for segfault logging in 2.6.6

Andi, the logging in vanilla 2.6.6 seems to be broken: Only catched segfaults
get logged.  With this patch it works more like intended for me.

Hi,

The ! for SIGSEGV was indeed wrong. Thanks for catching this. I will fix this.

But the unhandled_signal() change itself is imho not correct. What the 
check does is to match when PT_PTRACED is set, but fail when PT_TRACESYSGOOD
(= strace running) is set. As far as I can see the original code for this 
is correct.

Overall there must be still some other problem, because these printks
have no relation to how the program works (except for making it a bit slower)

Ah.  Then my strace probably is too old, it doesn't seem to use 
PTRACE_O_TRACESYSGOOD.

We'll release 1.4.2-fcs in few days.  It has a lot x86_64 specific fixes (and
also works on EMT64 machines).  If the bug reporter still has problems (except
for bogus segfault logs) with that version, he should report it at Blackdown.

32-bit JVMs on the other hand already _should_ work fine.

ok, I retested my own Java code and it does indeed work fine despite the kernel
messages. i noticed the fix for the false messages also made it into the vanilla
kernel, so I'm going to close this one.

sorry for the confusion.

-m