RFR: 8072147: Preloading libjsig.dylib causes deadlock when signal() is called

Daniel D. Daugherty daniel.daugherty at oracle.com
Mon Jun 29 21:42:09 UTC 2015


On 6/29/15 10:41 AM, david buck wrote:
> Hi Dmitry!
>
> I have fixed the issue and retested both manually and with the 
> "hotspot" test suit. Thank you again for the catch.
>
> http://cr.openjdk.java.net/~dbuck/8072147/webrev.01/

src/os/bsd/vm/jsig.c
     No comments.

Thumbs up.

Dan


>
> Hi Karen!
>
> The "reenter" boolean is thread local, so it should already work 
> exactly as you describe below.
>
> > p.s. let me see if I can find any existing signal handler chaining 
> tests - I suspect you will need to write some
> > additional ones
>
> I took a look, but was not able to find any tests that run actually 
> run on all *nix platforms and install signal handlers. Ultimately we 
> should have some sort of comprehensive functional testing for this. If 
> there already is such testing, I would like to add this particular 
> case. But I suspect that there is nothing comprehensive at the moment. 
> If so, I believe adding new functional testing for all of libjsig is 
> probably outside the scope of this point fix.
>
> Cheers,
> -Buck
>
> On 2015/06/30 1:27, Karen Kinnear wrote:
>> David,
>>
>> Thank you for tackling this bug.
>>
>> I don't understand how the proposed solution handles multiple threads
>>    - e.g. 2 jni threads installing their signal handlers and a jvm 
>> installing its signal handlers
>>
>> The jsig code is written to handle multi-threaded timing:
>>     user installs first, jvm installs after
>>        user install in progress, jvm tries to install
>>     jvm installs first, user installs after
>>        jvm install in progress, user tries to install
>>
>> I think having a global reentry, that only gets set to true on the 
>> first call_os_signal, means
>> that the chaining won't be installed properly.
>>
>> I wonder if what you are looking for is a way to track that a given 
>> thread is currently
>> inside this logic
>>     - not a global state
>>     - not whether a given thread has ever called this (a thread may 
>> call this code multiple times, one for each signal)
>>     - but whether we have a recursive call.
>>
>> So - perhaps there is a way to track a list of threads that are in 
>> the os_signal call and the thread
>> that owns the signal_lock?  So if you are in the sigaction call you 
>> can check if your thread already
>> owns the signal_lock and if it is in the os_signal call - and skip 
>> both the lock and unlock (basically making
>> a reentrant lock). And then when you are done the os_signal call, 
>> remove your thread from the list
>> of threads in the os_signal call before returning from call_os_signal.
>>
>> That way the lock will still work between threads and between a 
>> requests by the same thread.
>>
>> Does that sounds worth exploring?
>>
>> thanks,
>> Karen
>>
>> p.s. let me see if I can find any existing signal handler chaining 
>> tests - I suspect you will need to write some
>> additional ones
>>
>>
>> On Jun 29, 2015, at 10:35 AM, david buck wrote:
>>
>>> Hi Dmitry!
>>>
>>> Ouch. Yes, that is *very* wrong. I will fix and retest.
>>>
>>> Sorry for the trivial error and thank you for the catch!
>>>
>>> Cheers,
>>> -Buck
>>>
>>> On 2015/06/29 23:31, Dmitry Dmitriev wrote:
>>>> Hello David,
>>>>
>>>> In call_os_signal function you add "reentry = false;"(line 93) after
>>>> return statement and it seems as unreachable code.
>>>>
>>>> Thanks,
>>>> Dmitry
>>>>
>>>> On 29.06.2015 17:18, david buck wrote:
>>>>> Hi!
>>>>>
>>>>> Please review my fix below:
>>>>>
>>>>> bug report: https://bugs.openjdk.java.net/browse/jdk-8072147
>>>>>
>>>>> webrev: http://cr.openjdk.java.net/~dbuck/8072147/webrev.00/
>>>>>
>>>>> The fix is intentionally limited only to the platform (OSX/BSD) and
>>>>> scenario (signal() implemented by means of a direct call to
>>>>> sigaction()) where we can reasonably expect to see (and therefor 
>>>>> test)
>>>>> this issue.
>>>>>
>>>>> Fix has been manually tested for effectiveness by myself. "hotspot"
>>>>> test suite run and passed on all platforms.
>>>>>
>>>>> Cheers,
>>>>> -Buck
>>>>
>>



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