RFR: 8027429: Add diagnostic command VM.info to get hs_err print-out

David Holmes david.holmes at oracle.com
Mon Nov 2 01:45:27 UTC 2015 

On 30/10/2015 8:38 PM, Mattis Castegren wrote:
> Hi
>
> I agree that there may be things we could add to VM.info that we couldn't add in an hs_err file due to the fact that we are crashing. However, I really do believe that we should use the same code. The goal of the hs_err file is exactly the same as the goal of VM.info, to print as much information about the system as possible so that when we look at an hs_err file or the output from VM.info, we get as much information about the system as possible. That way we can reduce the need to go back and forth with the customer to ask for more information.
>
> If we enumerate what we need in VM.info, the list would look very much like what we already do in VMError, and therefore I think we should use the same code. If we find something that we would want, that is not currently printed in hs_err files, I think we have two options:
>
> 1) Add it to hs_err files as well. If it is interesting when gathering customer information before a crash, it probably is interesting after a crash
> 2) If it for some reason cannot be captured when crashing, add it to the code with the condition that we don't print it during crash time.
>
> I would therefore suggest the following plan of action
>
> 1) Review and push this fix to see if there are any technical issues with regards to thread safety, etc. I know David has had this in mind when doing the change. After that, we have a command that support can use.
> 2) Think about if there is any information missing, both from hs_err files and from VM.info. Here, we may want to ask support about if there is any additional information they need to ask for when they get this data. If possible, this information should be added to both hs_err files and VM.info, we don't want support to have to ask for VM.info if we already have an hs_err file. Of course, if there is anything Dev would want to see when analyzing crashes in testing, we should add that too.

I have no issue with VMError and VM.Info using the same code (where 
appropriate), but I think it wrong to try and implement VM.Info directly 
using the actual VMError mechanism. It is crude and makes it difficult 
to make independent changes to either facility.

Sorry.

David


> Kind Regards
> /Mattis
>
> -----Original Message-----
> From: David Holmes
> Sent: den 29 oktober 2015 23:20
> To: Mattis Castegren; Coleen Phillimore; hotspot-runtime-dev at openjdk.java.net
> Subject: Re: RFR: 8027429: Add diagnostic command VM.info to get hs_err print-out
>
> On 29/10/2015 11:36 PM, Mattis Castegren wrote:
>> Some background: We have this command in JRockit. The information you gather when you crash to give a good summary of what system you run on is pretty much exactly the information you need to get a good summary on a system that has not crashed. The JRockit command is extremely useful for support, and saves a lot of work going back and forth asking about system information.
>>
>> Also, if we write something new in the hs_err file, like if there has been any out of memory errors, we often would want the same information in the VM.info output. From my experience in Sustaining/Support, I can't think of any information you would want in VM.info that you wouldn't also want in the hs_err file and the other way around, apart from details about the crash (obviously).
>>
>> I don't see a reason to exactly enumerate what information VM.info should provide. From a sustaining/support perspective, we want a one-stop command to gather as much useful information as possible, which is the same idea we have for the hs_err file.
>
> The reason to enumerate what is required is to see where that information already exists and can be collected from. The VMError report has to be very careful about what it does and how it does it because of the fact we may have crashed and the general process state is indeterminate. A Dcmd can simply gather whatever information is required from the available sources in whatever order or format desired.
>
> I have no problem with this command, just how it has been proposed to implement it.
>
> David
>
>> Kind Regards
>> /Mattis
>>
>> -----Original Message-----
>> From: David Holmes
>> Sent: den 29 oktober 2015 13:08
>> To: Coleen Phillimore; hotspot-runtime-dev at openjdk.java.net
>> Subject: Re: RFR: 8027429: Add diagnostic command VM.info to get
>> hs_err print-out
>>
>> On 29/10/2015 10:02 PM, Coleen Phillimore wrote:
>>>
>>>
>>> On 10/29/15 7:58 AM, David Holmes wrote:
>>>> On 29/10/2015 9:26 PM, Coleen Phillimore wrote:
>>>>>
>>>>> So I actually disagree.  I don't think there should be an
>>>>> additional separate mechanism to get the same information that we
>>>>> get with hs_err reporting.  I've wanted to have a feature like this for a long time.
>>>>>
>>>>> I pre-reviewed this change and I thought it looked good in general.
>>>>> I didn't see the thread iteration problem that Fred refers to
>>>>> below, but I think the individual problems can be fixed.
>>>>>
>>>>> The last thing I want is this code to be copied somewhere else.
>>>>
>>>> Factored as needed not copied. VMError is not an "info" reporting
>>>> mechanism.
>>>
>>> If you look at the things that are reported in each "STEP", there's a
>>> small amount of code and the order is important.
>>
>> The order is less important in an "info" request I would think.
>>
>>> I'd like the vm info to use the same order and report what it can do
>>> safely.   Refactoring 5 lines of code into functions doesn't make sense.
>>
>> I need to consider exactly what it is the "info" needs to report in
>> more detail. There are existing facilities (system properties,
>> management
>> APIs) for various bits of runtime information, which VMError can't utilize but a Dcmd can.
>>
>> David
>>
>>> Coleen
>>>
>>>>
>>>> David
>>>>
>>>>> Coleen
>>>>>
>>>>> On 10/28/15 8:48 PM, David Holmes wrote:
>>>>>> I agree with Fred, this kind of info reporting should not be
>>>>>> piggy-backed onto VMError handling for the reasons stated (and the
>>>>>> error handling logic is complicated enough as it is!). For things
>>>>>> like thread lists there are already safe management functions that
>>>>>> can/should be used.
>>>>>>
>>>>>> Thanks,
>>>>>> David H.
>>>>>>
>>>>>> On 29/10/2015 3:29 AM, Frederic Parain wrote:
>>>>>>> Hi David,
>>>>>>>
>>>>>>> I haven't review all the code yet, but I'm concerned with the
>>>>>>> fact that the diagnostic command is calling VMError::report().
>>>>>>> This method has been implemented to be executed in the particular
>>>>>>> context of fatal errors, and its usage while the VM is running
>>>>>>> normally seems dangerous.
>>>>>>>
>>>>>>> For instance, VMError::report() consciously avoids grabbing locks
>>>>>>> because of the risk of deadlock during the error reporting.
>>>>>>> The consequence is that some data structures are browsed in an
>>>>>>> unsafe way. One example: VMError::report() calls
>>>>>>> Threads::print_on_error() which iterates over the thread list
>>>>>>> *without owning the Threads_lock*.
>>>>>>>
>>>>>>> The implementation of the diagnostic command seems also to
>>>>>>> exclude a lot of reporting from the initial VMError::report()
>>>>>>> method. Have you considered implementing a new MT-safe reporting
>>>>>>> method rather than trying to modify the special VMError::report()
>>>>>>> methods? (Note that some code factorization between
>>>>>>> VMError::report() and this new method should be possible).
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Fred
>>>>>>>
>>>>>>> On 28/10/2015 17:18, david buck wrote:
>>>>>>>> Hi!
>>>>>>>>
>>>>>>>> Please review my change for this small enhancement.
>>>>>>>>
>>>>>>>> bug: https://bugs.openjdk.java.net/browse/JDK-8027429
>>>>>>>> webrev: http://cr.openjdk.java.net/~dbuck/8027429_jdk9_01/
>>>>>>>>
>>>>>>>> Cheers,
>>>>>>>> -Buck
>>>>>>>
>>>>>
>>>

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