RFR: 8215355: Object monitor deadlock with no threads holding the monitor (using jemalloc 5.1)

[Thomas Stüfe]

This is evil :)

There might be more cases like this, e.g.

frame_x86.cpp  frame::is_interpreted_frame_valid():

if (locals > thread->stack_base() || locals < (address) fp()) return false;

Also, I would have thought the little alloca() dance we do at the start
of thread_native_entry() would push the first real frame down the stack.

The fix looks good.

Cheers, Thomas



On Mon, Nov 18, 2019 at 3:31 AM David Holmes <david.holmes at oracle.com>
wrote:

> Bug: https://bugs.openjdk.java.net/browse/JDK-8215355
> webrev: http://cr.openjdk.java.net/~dholmes/8215355/webrev/
>
> This was a very difficult bug to track down and I want to publicly
> acknowledge and thank the jemalloc folk (users and developers) for
> continuing to investigate this issue from their side. Without their
> persistence this issue would have languished.
>
> The thread stack_base() is the first address above the thread's stack.
> However, the "in stack" checks performed by Thread::on_local_stack and
> Thread::is_in_stack allowed the checked address to be equal to the
> stack_base() - which is not correct. Here's how this manifests as the bug:
>
> - Let a JavaThread instance, T2, be allocated at the end of thread T1's
> stack i.e. at T1->stack_base()
>    [This seems to be why this only reproduced with jemalloc.]
> - Let T2 lock an inflated monitor
> - Let T1 try to lock the same monitor
>    - T1 would consider the _owner field value (T2) as being in its stack
> and so consider the monitor stack-locked by T1
>    - And so both T1 and T2 would have ownership of the monitor allowing
> the monitor state (and application state) to be corrupted. This results
> in a range of hangs and crashes depending on the exact interleaving.
>
> Interestingly Thread::is_in_usable_stack does not have this bug.
>
> The bug can be tracked way back to JDK-6699669 as explained in the bug
> report. That issue also showed that the same bug existed in the SA
> implementations of these "on stack" checks.
>
> Testing:
>    - The reproducer from the bug report, using jemalloc, ran over 5000
> times without failing in any way.
>    - tiers 1-3 on all Oracle platforms
>    - serviceability/sa tests
>
> Thanks,
> David
> -----
>