[10]RFR: 6415680: (bf) MappedByteBuffer.get() can provoke crash with EXCEPTION_IN_PAGE_ERROR

[jamsheed]

Hi Dean,

revised webrev:

http://cr.openjdk.java.net/~jcm/6415680/webrev.01/

i agree to the comment that it is potentially unsafe to assume the 
implementation, and count can be in autoincrement mode. so with this bug 
i would like to deal with only

the single value access error handling.

revised webrev: http://cr.openjdk.java.net/~jcm/6415680/webrev.01/

Best regards,

Jamsheed



On Tuesday 14 November 2017 11:57 PM, dean.long at oracle.com wrote:
> Adding runtime alias...
>
> comments inlined below.
>
>
> On 11/13/17 9:10 PM, jamsheed wrote:
>
>> Hi, request for review, jbs: 
>> https://bugs.openjdk.java.net/browse/JDK-6415680 webrev: 
>> http://cr.openjdk.java.net/~jcm/6415680/webrev.00/ Description: 1) 
>> changes equivalent to JDK-4454115 is done for windows.
>
> It looks like "nm" can be uninitialized if "in_java" is false.
>
>> 2) added guard to multiple value access sites, Unsafe_CopyMemory0, 
>> Unsafe_SetMemory0 and Unsafe_CopySwapMemory0.
>
> Can you narrow the scope of the unsafe access using something like 
> GuardUnsafeAccess, instead of marking the whole function as doing 
> unsafe access?
>
> There are some risks with trying to  abort a copy function.
>
> First, won't we get multiple exceptions until we finally hit the end 
> of the range?  What if the bad range is very large?
>
> Second, what if the loop is using auto-increment instructions? 
> Skipping to the next instruction would mean we loop forever if the 
> increment never happens.
>
> I think if we are going to safely abort copy functions then we need to 
> register them as a kind of CodeBlob that has a special abort entry 
> point or exception handler we can redirect to, or maybe pop the whole 
> frame and return.
>
> Is there really a problem with these copy functions?  I'm wondering 
> why Mikael did not identify these as a problem in 8154592.
>
>> 3) Unsafe_CopySwapMemory0 is JVM_LEAF so removed 
>> thread->thread_state() == _thread_in_vm checks from signal handler
>
> How about adding a check for _thread_in_native instead of removing the 
> check entirely?
>
> dl
>
>> Best regards, Jamsheed
>>
>