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.
-------------
Commit messages:
- fix
Changes: https://git.openjdk.org/jdk/pull/26031/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26031&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8359366
Stats: 10 lines in 2 files changed: 8 ins; 0 del; 2 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
