RFR(s): 8152182: Possible overflow in initialzation of _rescan_task_size and _marking_task_size

[Jon Masamitsu]

Sangheon,

It occurs to me that if you created a function in CMS code 
check_rescan_task_size_alignment()
to do the check

> 506 const size_t rescan_task_size = cms->cmsSpace()->rescan_task_size();
> 507 const size_t alignment = CardTableModRefBS::card_size * BitsPerWord;
> 508
> 509 if ((size_t)round_to((intptr_t)rescan_task_size, alignment) != 
> rescan_task_size) {

then you won't have to expose the particular alignment requirements in the
constraint function.  The code could look more like

if ( check_rescan_task_size_alignment() ) {

513 CommandLineError::print(verbose,
514 "Rescan task size (" SIZE_FORMAT " = CMSRescanMultiple * "
515 "CardTableModRefBS::card_size_in_words * BitsPerWord) must be "
516 "aligned to CardTableModRefBS::card_size * BitsPerWord (" 
SIZE_FORMAT "). "
517 "Round-down value for CMSRescanMultiple is " SIZE_FORMAT "\n",
518 rescan_task_size, alignment, round_down_value);
519 status = Flag::VIOLATES_CONSTRAINT;

}


You might be able to do something similar in the other constraint function.

Also for

472 if (value > addr_ergo_max) {
473 CommandLineError::print(verbose,
474 "%s (" SIZE_FORMAT ") must be "
475 "less than or equal to ergonomic maximum (" SIZE_FORMAT ") "
476 "based on start address corresponds to the old generation of the 
Java heap\n",
477 name, value, addr_ergo_max);
478 return Flag::VIOLATES_CONSTRAINT;
479 }

Printing the addr_ergo_max might be confusing to the  users since it 
will be a very large
number.  Not sure what  to do unless you can print a maximum value of 
the flag based
on the maximum heap size (instead of based on MAX_SIZE).

Ask if that's not clear.

Jon



On 4/5/2016 10:24 AM, sangheon wrote:
> Hi all,
>
> Please review this change for CMSRescanMultiple and 
> CMSConcMarkMultiple flags.
>
> Both flags are set by "CardTableModRefBS::card_size_in_words * 
> BitsPerWord * flag" which potentially would make an overflow with 
> their maximum value without setting range. And these flags also would 
> make an arithmetic overflow when calculating with the size and the 
> start address of reserved area. In addition, CMSRescanMultiple needs 
> an alignment check.
>
> CR: https://bugs.openjdk.java.net/browse/JDK-8152182
> Webrev: http://cr.openjdk.java.net/~sangheki/8152182/webrev.00
> Testing: JPRT, runtime/commandline JTREG for all platforms
>
> Thanks,
> Sangheon