RFR (s) 8251383: Disable Event::log from linux_mprotect when processing the assertion poison page

[David Holmes]

Thanks for the review Dan!

David

On 12/08/2020 2:22 am, Daniel D. Daugherty wrote:
> On 8/11/20 5:17 AM, David Holmes wrote:
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8251383
>> webrev: http://cr.openjdk.java.net/~dholmes/8251383/webrev/
> 
> src/hotspot/os/linux/os_linux.cpp
>      No comments.
> 
> Thumbs up.
> 
> Dan
> 
>>
>> When the assertion poison page is enabled (Linux only and on by 
>> default) the signal handler will call os::protect_memory to change the 
>> page protection bits. That will call linux_mprotect which will call
>>
>> Events::log(NULL, "Protecting memory [" INTPTR_FORMAT "," 
>> INTPTR_FORMAT "] with protection modes %x", p2i(bottom), 
>> p2i(bottom+size), prot);
>>
>> Event logging in turn can use Mutexes and other VM facilities - all of 
>> which are now being executed in a signal handling context (which is 
>> inherently unsafe). It also means that there cannot be any other 
>> failing assertions on that path as you will re-trigger the poison page 
>> pagefault and abort with no hs_err file. Hence, as happened to me, a 
>> failing assertion in the mutex code triggers this problem.
>>
>> The issue can be worked-around by setting -XX:-ShowRegistersOnAssert 
>> (once you realise what is happening).
>>
>> The simple fix is to skip the logging if the faulting address is the 
>> poison page address.
>>
>> This only affects debug builds of course.
>>
>> Testing:
>>   - runtime/ErrorHandling
>>   - tier 1-3
>>
>> Thanks,
>> David
>