RFR(s): 8065895: Synchronous signals during error reporting may terminate or hang VM process

David Holmes david.holmes at oracle.com
Thu Feb 5 02:12:32 UTC 2015

Thomas, Gerard,

I pushed the changes but didn't realize that hg import wouldn't hg add 
the new test file and so it got left behind. But I then realized that 
the test should be named/located differently as we don't structure the 
tests on bug number any more. So I will file a new bug and rename and 
relocate the test, and then push that:



On 4/02/2015 8:18 PM, David Holmes wrote:
> On 4/02/2015 8:15 PM, Thomas Stüfe wrote:
>> Great, thank you!
>> @David: Do you still need something from me to sponsor the change?
> No I think I have everything I need. Will push it in the morning.
> You'll be listed as Contributor as you don't have Author status for jdk9
> project.
> Thanks,
> David
>> Kind Regards, Thaoms
>> On Tue, Feb 3, 2015 at 10:15 PM, Gerard Ziemski
>> <gerard.ziemski at oracle.com <mailto:gerard.ziemski at oracle.com>> wrote:
>>     Looks good! Thank you for a great fix!
>>     cheers
>>     On 2/3/2015 10:40 AM, Thomas Stüfe wrote:
>>>     Hi Gerard,
>>>     thank you for your feedback! See here my new change:
>>>     http://cr.openjdk.java.net/~stuefe/webrevs/8065895/webrev.07/webrev/
>>> <http://cr.openjdk.java.net/%7Estuefe/webrevs/8065895/webrev.07/webrev/>
>>>     On Mon, Feb 2, 2015 at 4:19 PM, Gerard Ziemski
>>>     <gerard.ziemski at oracle.com <mailto:gerard.ziemski at oracle.com>>
>>> wrote:
>>>         hi Thomas,
>>>         On 2/1/2015 9:56 AM, Thomas Stüfe wrote:
>>>>         On Fri, Jan 30, 2015 at 11:23 PM, Gerard Ziemski
>>>>         <gerard.ziemski at oracle.com
>>>>         <mailto:gerard.ziemski at oracle.com>> wrote:
>>>>             hi Thomas,
>>>>             #1 The following comment in vmError_bsd.cpp,
>>>>             vmError_linux.cpp and vmError_solaris.cpp is now outdated
>>>>             and should be updated from:
>>>>             // handle all synchronous program error signals which may
>>>>             happen during error
>>>>             // reporting. They must be unblocked, caught, handled.
>>>>             //
>>>>             // Note that in hotspot signal handlers are installed
>>>>             with a fully filled
>>>>             // signal mask, i.e. upon delivery all signals - also
>>>>             synchronous error signals
>>>>             // - are blocked. For synchronous error signals this is
>>>>             deadly - program will
>>>>             // hang or be terminated immediately if secondary errors
>>>>             happen during error
>>>>             // reporting.
>>>>             to the comment from vmError_aix.cpp:
>>>>             // Handle all synchronous signals which may happen during
>>>>             signal handling,
>>>>             // not just SIGSEGV and SIGBUS.
>>>>         I am not sure I understand: the problem is that signal
>>>>         handlers are installed in the hotspot with sa_mask completely
>>>>         set, so all signals are blocked. See e.g. os_linux.cpp, line
>>>>         4304++ (os::Linux::set_signal_handler()). So the comment
>>>>         appears to be correct.
>>>         We continue to block the signals initially, but the comment,
>>>         or at least its last sentence, does not apply anymore because
>>>         of the crux of your fix - ie. the program will not hang
>>>         because we immediately unblock the synchronous traps in the
>>>         crash handler. So maybe we should make that clear in that
>>> comment?
>>>     Okay, I see that now. I modified the comments as you suggested
>>>     earlier.
>>>>         POSIX itself mentioned only the four, see documentation on
>>>>         sigprocmask:
>>>>         "If any of the SIGFPE, SIGILL, SIGSEGV, or SIGBUS signals are
>>>>         generated while they are blocked, the result is undefined,
>>>>         unless the signal was generated by the /kill/()
>>>> <http://pubs.opengroup.org/onlinepubs/009695399/functions/kill.html>
>>>> function,
>>>>         the /sigqueue/()
>>>> <http://pubs.opengroup.org/onlinepubs/009695399/functions/sigqueue.html>
>>>> function,
>>>>         or the /raise/()
>>>> <http://pubs.opengroup.org/onlinepubs/009695399/functions/raise.html> function."
>>>>         I added SIGTRAP on AIX because it is synchronously delivered
>>>>         too, but do not know any other signals. I am happy to add any
>>>>         other signals you know of.
>>>         Nope, I do not know any more synchronous signals - just wanted
>>>         to make sure we take a second look and collectively agree that
>>>         this list is exhaustive.
>>>>         I would like to test it at least twice, to see that signal
>>>>         handling continues to work after secondary handler ran once.
>>>>         It needs to correctly unset the signal mask for the
>>>>         synchronous signals.
>>>>         Executing it four times may be a bit excessive; if you
>>>>         prefer, I can remove it for the out_done case.
>>>>         Note that there is one benefit of repeatedly crashing in the
>>>>         error handler, it is to stress the stack usage during error
>>>>         reporting. But I admit that this test could be done much
>>>> better.
>>>         It's a bit confusing at first when someone debugs this code
>>>         and sees four of those secondary signals coming through, so
>>>         maybe just a small comment here would suffice?
>>>     I changed the coding to only fire for the log case. That should be
>>>     less confusing.
>>>>         vmerrors.sh is very minimal. The bug symptom was incomplete
>>>>         or empty hs-err files, and you would not catch this with the
>>>>         vmerrors.sh test, would you not? You also can reproduce this
>>>>         bug only by using both -XX:ErrorHandlerTest and
>>>>         -XX:TestCrashInErrorHandler together, so it does not quite
>>>>         fit into what vmerrors.sh does.
>>>>         At SAP we have a nice test suite which crashes the VM in a
>>>>         number of ways and then checks whether the hs-err files are
>>>>         complete (enough). I was planning to add a Jtreg test which
>>>>         does something similar, but did not add it to this change
>>>>         because I did not want to make the change larger than
>>>> necessary.
>>>         I would think that the added complexity of the test case,
>>>         would in fact make it easier to review the test with the fix
>>>         at the same time. Also, since the test in this case is
>>>         feasible, isn't it recommended to have the fix committed along
>>>         with its test?
>>>     I added a small jtreg test. Note that the test cannot really
>>>     demonstrate the bug without my fix, because it needs the new
>>>     -XX:TestCrashInErrorHandler options which is part of the fix. But
>>>     it will show regressions.
>>>         cheers
>>>     Best Regards, Thomas

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