RFR: 8354523: runtime/Monitor/SyncOnValueBasedClassTest.java triggers SIGSEGV

[Coleen Phillimore]

On Tue, 15 Apr 2025 12:47:47 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> When DiagnoseSyncOnValueBasedClasses is != 0, then we can take the slow-path without having cleared the monitor cache in the BasicLock. This would later lead to a crash or other unexpected behaviour. This can happen with C1 or the interpreter, C2 has the DiagnoseSyncOnValueBasedClasses-block after clearing the cache, and the native-entry in sharedRuntime_x86_64.cpp does not have a DiagnoseSyncOnValueBasedClasses-block at all.
> 
> The proposed fix so far is a bit ugly because it repeats the clearing code in 3 places. The alternative would be to move the DiagnoseSyncOnValueBasedClasses-block into MA::lightweight_lock(), but this would bring DiagnoseSyncOnValueBasedClasses-handling into the native entry in sharedRuntime_x86_64.cpp, which is currently not the case. Also, we don't have enough regs for that, but we can probably use rscratch1 now that 32-bit is gone (as is already done in C1 and interpreter paths anyway).
> 
> I'd first settle on the structure, and then implement the same thing for aarch64.
> ping @xmas92

I wonder if it would be better to zero the cache in InterpreterRuntime::monitorenter and have a C1 entry rather than going directly to monitor_enter_helper.  Then we can zero the BasicLock::monitor_cache in the two places where it shouldn't be set.

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PR Comment: https://git.openjdk.org/jdk/pull/24660#issuecomment-2806841185