RFR[13, xs]: 8227275: Within native OOM error handling, assertions may hang the process

[Thomas Stüfe]

Great, thanks!

.. Thomas

On Wed, Jul 10, 2019 at 3:02 PM <coleen.phillimore at oracle.com> wrote:

>
>
> On 7/10/19 1:38 AM, Thomas Stüfe wrote:
>
>
> Hi Coleen,
>
> thanks for looking at it! Remarks below.
>
> On Tue, Jul 9, 2019 at 11:12 PM <coleen.phillimore at oracle.com> wrote:
>
>>
>>
>> http://cr.openjdk.java.net/~stuefe/webrevs/8227275-native-oom-hanging-assertions/webrev.00/webrev/src/hotspot/share/utilities/debug.cpp.udiff.html
>>
>> I don't understand why you don't just leave the poison page PROT_NONE
>> and call this from handle_assert_poison_fault?
>>
>> +void disarm_assert_poison() {
>> + g_assert_poison = &g_dummy;
>> +}
>> +
>>
>> Then you don't have to check that it succeeded.   At this point, it
>> doesn't matter.
>>
>>
> Because unfortunately that does not work. At the point it is too late.
>
> handle_assert_poison_fault() is called from the signal handler to handle a
> poison touch SIGSEGV. When it is handled, it will return to the caller -
> jumps back to the instruction triggering the SEGV. There, poison page
> address is already loaded into a register and cannot be changed.
>
>
> Oh, I see.  Thank you for the explanation.  Looks good to me then.
>
> Coleen
>
>
> The only other choice we have, beside removing the write protection from
> the poison page, is not to return to the caller. That is what happens when
> I return false from handle_assert_poison_fault(). In that case the signal
> handler proceeds as if this were a real SEGV.
>
> Cheers, Thomas
>
>
> Coleen
>>
>> On 7/9/19 5:23 AM, Thomas Stüfe wrote:
>> > Dear all,
>> >
>> > may I please have reviews for the following issue:
>> >
>> > JBS: https://bugs.openjdk.java.net/browse/JDK-8227275
>> > cr:
>> >
>> http://cr.openjdk.java.net/~stuefe/webrevs/8227275-native-oom-hanging-assertions/webrev.00/webrev/
>> >
>> > Summary: on OOM, we may fail to disarm assertion poison page; this may
>> lead
>> > to endless loops during error handling if assertions happen in native
>> OOM
>> > scenarios.
>> >
>> > For more details, pls see the JBS issue.
>> >
>> > Thanks, Thomas
>>
>>
>