Hi Volker,
Thanks for looking at this.
On 5/08/2016 1:48 AM, Volker Simonis wrote:
Hi David,
thanks for doing this change on all platforms.
The fix looks good. Maybe you can just extend the following comment with
something like:
// Note that the SR_lock plays no role in this suspend/resume protocol.
// It is only used in SR_handler as a thread termination indicator if
NULL.
Darn this code is confusing - too many "SR"'s :( I have added
// Note that the SR_lock plays no role in this suspend/resume protocol,
// but is checked for NULL in SR_handler as a thread termination indicator.
Updated webrev:
http://cr.openjdk.java.net/~dholmes/8159461/webrev.v2/
This also reminded me to follow up on why the Solaris SR_handler is
different and I found it is not actually installed as a direct signal
handler, but is called from the real signal handler if dealing with a
JavaThread or the VMThread. Consequently the Solaris version of the
SR_handler can not encounter this specific bug and so I have reverted
the changes to os_solaris.cpp
Thanks,
David
Regards,
Volker
On Wed, Aug 3, 2016 at 3:13 AM, David Holmes <david.hol...@oracle.com
<mailto:david.hol...@oracle.com>> wrote:
webrev: http://cr.openjdk.java.net/~dholmes/8159461/webrev/
<http://cr.openjdk.java.net/~dholmes/8159461/webrev/>
bug: https://bugs.openjdk.java.net/browse/JDK-8159461
<https://bugs.openjdk.java.net/browse/JDK-8159461>
The suspend/resume signal (SR_signum) is never sent to a thread once
it has started to terminate. On one platform (SuSE 12) we have seen
what appears to be a "stuck" signal, which is only delivered when
the terminating thread restores its original signal mask (as if
pthread_sigmask makes the system realize there is a pending signal -
we already check the signal was not blocked). At this point in the
thread termination we have freed the osthread, so the the SR_handler
would access deallocated memory. In debug builds we first hit an
assertion that the current thread is a JavaThread or the VMThread -
that assertion fails, even though it is a JavaThread, because we
have already executed the ~JavaThread destructor and inside the
~Thread destructor we are a plain Thread not a JavaThread.
The fix was to make a small adjustment to the thread termination
process so that we delete the SR_lock before calling
os::free_thread(). In the SR_handler() we can then use a NULL check
of SR_lock() to indicate the thread has terminated and we return.
While only seen on Linux I took the opportunity to apply the fix on
all platforms and also cleaned up the code where we were using
Thread::current() unsafely in a signal-handling context.
Testing: regular tier 1 (JPRT)
Kitchensink (in progress)
As we can't readily reproduce the problem I tested this by having a
terminating thread raise SR_signum directly from within the ~Thread
destructor.
Thanks,
David
