RFR: 8359366: RunThese30M.java EXCEPTION_ACCESS_VIOLATION in JvmtiBreakpoints::clearall_in_class_at_safepoint [v2]

[Leonid Mesnik]

> The segv/eav happens in the case if JvmtiBreakpoint::_method's class redefined old between getting the Method* from jmethodid in the 
> JvmtiEnv::SetBreakpoint(Method* method, jlocation location) {..} and 
> and actual setting breakpoint in the VM operation VM_ChangeBreakpoints.
> 
> Here are details:
> The breakpoint is set in 2 steps.
> 1) method jvmti_SetBreakpoint(jvmtiEnv* env, jmethodID method,  jlocation location)  convert jmethodID to Method* and call 
>  JvmtiEnv::SetBreakpoint(Method* method, jlocation location)
> where 
>   JvmtiBreakpoint bp(method, location);
> is created with this Method* 
> Note: it is done while thread is in VM state, so Method can't become is_old while this is done.
>  
> 2) The VMOp is used to add breakpoint into the list 
>  VM_ChangeBreakpoints set_breakpoint(VM_ChangeBreakpoints::SET_BREAKPOINT, &bp);
>   VMThread::execute(&set_breakpoint);
> to call  JvmtiBreakpoints::set_at_safepoint()
> that can modify JvmtiBreakpoints list and set breakpoint in safepoint without synchronization.
> 
> So it might be possible that class redefinition  VM_RedefineClasses  operation that redefine the class with this breakpoint happens between steps 1) and 2)
> VM_RedefineClasses::redefine_single_class()
> clear all class-related breakpoints in the JvmtiBreakpoints, however the "problematic" breakpoint is in VMThread  queue and thus we are still continue to do this operation.
> So in the step 2) the the JvmtiBreakpoint with 'is_old' method is added to the JvmtiBreakpoints and breakpoint is set.
> 
> Then old method mights be purged any time once  they are not on the stack and any access to this breakpoint could lead to usage of Metthod* _method pointing to deallocated metaspace.
> 
> The VM_RedefineClasses clear all breakpoints so it is correct just to don't proceed with current breakpoint also.
> 
> Looks, like very unlikely but reproducing with stress test after some time.
> Verified that the crash is not reproduced anymore with corresponding test after the fix.
> 
> Many thanks to Coleen for detailed explanation of class redefinition.

Leonid Mesnik has updated the pull request incrementally with one additional commit since the last revision:

  changed jmethodid to methodHandle.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/26031/files
  - new: https://git.openjdk.org/jdk/pull/26031/files/a6a9f01c..e1524bbd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26031&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26031&range=00-01

  Stats: 16 lines in 2 files changed: 8 ins; 2 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/26031.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26031/head:pull/26031

PR: https://git.openjdk.org/jdk/pull/26031