On Sat, 10 Oct 2026 10:16:21 GMT, Justus Garbe <[email protected]> wrote:
>> A rare bug with the jdk has recently been filed again: >> https://github.com/adoptium/adoptium-support/issues/1538, which reports the >> already seen behavior in JDK-8352077: `unhandled instruction`. The original >> issue was closed with no reproduction. I have managed to write a >> reproduction with the new data. >> >> It seems that it is caused by a missing null check in the >> `BreakpointInfo::set` path, which calls into: >> `incr_number_of_breakpoints` which calls `build_method_counters`. Which has >> multiple ways to return `nullptr` if either the oom flag is already set or >> the allocation fails, which is done via allocate_no_exception since it runs >> on a VMThread, therefore it cant actually call a GC or raise the metadata >> limit. Therefore incr_number_of_breakpoints, never increases the number >> (since method counters is nullptr). Compilation is then paused, because the >> method cannot increase it's invocation counter, then after a purge caused by >> a gc pass, the mark is unset. After that it can correctly create it's >> counter, but since it never captured the breakpoints, the breakpoint is 0. >> >> The method then can be picked up by a compiler thread since >> `number_of_breakpoints` is now 0 and a counter is real it falsely passes >> `Method::is_not_compilable`. Then it copies the bytecode containing the >> `breakpoint` instruction, and doesn't invoke the clean function since the >> breakpoint count reports '0'. This causes a crash in the `ciBytecodeStream` >> since `ciBytecodeStream::next_wide_or_table` assumes the only special >> bytecodes can be `wide` or a type of switch, and bytecode is a special >> length instruction. >> >> This also explains why this happens so rarely. For this to happen the >> following need to happen in succession: >> - The debugger must try to set breakpoints >> - The method must never have been run >> - Metadata space needs to be at the limit and not resized when its setting >> the breakpoints and set the oom flag >> - Class unloading must purge the flag afterwards >> - The method must get compiled hot while the breakpoint is still installed >> >> 3 of the 5 conditions already happen when debugging with jdwp normally, from >> platforms like intellij, the others are race / resource conditions that seem >> happen very rarely. >> >> For the fix i propose to check the method counter allocation before actually >> requesting a breakpoint set. Here done by checking if method counters are >> not null before sending the vm request. I also had to expand the user facing >> method to make sure the OOM error c... > > Justus Garbe has updated the pull request incrementally with one additional > commit since the last revision: > > Exclude test from tier1 Thank you for updates. Looks good. We will keep an eye on new test. Will problem list it if it start failing. ------------- Marked as reviewed by sspitsyn (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/33191#pullrequestreview-5554447468
