RFR: 6415680: (bf) MappedByteBuffer.get() can provoke crash with EXCEPTION_IN_PAGE_ERROR
david.holmes at oracle.com
Tue Nov 14 21:15:36 UTC 2017
On 15/11/2017 4:27 AM, 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
I tend to agree with this suggestion. The unsafe region should be as
narrow as possible.
> 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.
Jamsheed and I has some discussions on this on IM last week. I also
flagged the multiple exceptions as potentially problematic. I'm not sure
how things will behave if we trigger hundreds of faults in succession -
nor how long it will take. Aborting the whole loop, or frame, seems
preferable but I don't know how you would do that.
> Is there really a problem with these copy functions? I'm wondering why
> Mikael did not identify these as a problem in 8154592.
Good question. :) It seems quite obvious to me that if a single
load/store needs protection then bulk load/store would also need
protection. And Jamsheeds tests confirmed that.
>> 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?
>> Best regards, Jamsheed
More information about the hotspot-compiler-dev