RFR: 8366659: ObjectMonitor::wait() can deadlock with a suspension request [v13]

[Serguei Spitsyn]

On Wed, 19 Nov 2025 16:04:51 GMT, Anton Artemov <aartemov at openjdk.org> wrote:

>> Hi, please consider the following changes:
>> 
>> If suspension is allowed when a thread is re-entering an object monitor (OM), then a deadlock is possible:
>> 
>> The waiting thread is made to be a successor and is unparked. Upon a suspension request, the thread will suspend itself whilst clearing the successor. The OM will be left unlocked (not grabbed by any thread), while the other threads are parked until a thread grabs the OM and the exits it. The suspended thread is on the entry-list and can be selected as a successor again. None of other threads can be woken up to grab the OM until the suspended thread has been resumed and successfully releases the OM.
>> 
>> This can happen in two places where the successor could be suspended: 
>> 1:
>> https://github.com/openjdk/jdk/blob/6322aaba63b235cb6c73d23a932210af318404ec/src/hotspot/share/runtime/objectMonitor.cpp#L1897
>> 
>> 2:
>> https://github.com/openjdk/jdk/blob/6322aaba63b235cb6c73d23a932210af318404ec/src/hotspot/share/runtime/objectMonitor.cpp#L1149
>> 
>> The issues are addressed by not allowing suspension in case 1, and by handling the suspension request at a later stage, after the thread has grabbed the OM in `reenter_internal()` in case 2. In case of a suspension request, the thread exits the OM and enters it again once resumed. 
>> 
>> The JVMTI `waited` event posting (2nd one) is postponed until the suspended thread is resumed and has entered the OM again.  The `enter` to the OM (in case `ExitOnSuspend` did exit) is done without posting any events.
>> 
>> Tests are added for both scenarios. 
>> 
>> Tested in tiers 1 - 7.
>
> Anton Artemov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8366659: Refactored tests.

Thank you for update!

test/hotspot/jtreg/serviceability/jvmti/SuspendWithObjectMonitorWait/SuspendWithObjectMonitorWait1.java line 141:

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test/hotspot/jtreg/serviceability/jvmti/SuspendWithObjectMonitorWait/SuspendWithObjectMonitorWait2.java line 156:

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test/hotspot/jtreg/serviceability/jvmti/SuspendWithObjectMonitorWait/SuspendWithObjectMonitorWait3.java line 166:

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PR Review: https://git.openjdk.org/jdk/pull/27040#pullrequestreview-3484035013
PR Review Comment: https://git.openjdk.org/jdk/pull/27040#discussion_r2543018144
PR Review Comment: https://git.openjdk.org/jdk/pull/27040#discussion_r2543018979
PR Review Comment: https://git.openjdk.org/jdk/pull/27040#discussion_r2543019514