jdk11 SIGSEGV in G1CMTask::make_reference_grey

[Stefan Karlsson]

Small correction:

On 2022-05-11 14:49, Vitaly Davidovich wrote:
> Hi Stefan,
>
> On Wed, May 11, 2022 at 8:24 AM Stefan Karlsson 
> <stefan.karlsson at oracle.com> wrote:
>
>     Hi Vitaly,
>
>     A comment about the SI_KERNEL observation:
>
>     On 2022-05-10 15:34, Vitaly Davidovich wrote:
>     ...
>>     RAX=0x0101010101010164 is an unknown value
>     ....
>>     RAX contents in the register output of the report looks like an interesting
>>     pattern, but doesn't appear to be a valid address of anything yet the
>>     instruction is using it as the base of a load.  Also, si_addr in the
>>     siginfo claims the faulting address is actually NULL.  Not quite sure what
>>     to make of that yet.
>
>     We encountered the same SI_KERNEL / si_addr == 0x0 crashes while
>     working on ZGC. What I learned was that if you try to dereference
>     a pointer with high-order bits set (making the address larger than
>     TASK_SIZE), then you'll get these crashes where si_addr doesn't
>     tell you what the failing address was.
>
> Ah, thanks for sharing that!
>
>
>
>     Side note: For us, it resulted in weird behaviors when the signal
>     handler treated these SIGSEGVs as implicit NULL pointer
>     exceptions, and we later crashed for secondary reasons.
>
> Ouch, that must’ve been “fun” to debug :).
>
>     This does
>

This was supposed to say *does not*

StefanK

>     seem to apply to your situation, but I changed the signal handler
>     code and left a comment about this. See
>     PosixSignals::pd_hotspot_signal_handler in:
>
>     https://github.com/openjdk/zgc/blob/zgc_generational/src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp
>     <https://urldefense.com/v3/__https://github.com/openjdk/zgc/blob/zgc_generational/src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp__;!!ACWV5N9M2RV99hQ!IO69tIcDKsezK8233EzE1B_52s9S3KqtKUuZKQvSogl5q5i7yGZHjkcky6X2ysyXKec1J7EKKdoDNsh-MK8$>
>
>         if (sig == SIGSEGV && info->si_addr == 0 && info->si_code ==
>     SI_KERNEL) {
>     #ifndef AMD64
>     ...
>     #else
>           // An irrecoverable SI_KERNEL SIGSEGV has occurred.
>           // It's likely caused by dereferencing an address larger
>     than TASK_SIZE.
>           return false;
>     #endif
>         }
>
> <thumbs up>
>
>
>
>     StefanK
>
>>     Thanks!
>
> -- 
> Sent from my phone