Hi Serguei,
On 11/08/2020 3:21 am, [email protected] wrote:
Hi Richard and David,
The implementation looks good to me.
But I do not understand what the test is doing with all this counters
and recursions.
For instance, these fragments:
86 recursions = 0;
87 try {
88 recursiveMethod(1<<20);
89 } catch (StackOverflowError e) {
90 msg("Caught StackOverflowError as expected");
91 }
92 int target_depth = recursions-100; // spaces are missed around
the '-' sigh
It is not obvious that the 'recursion' is updated in the recursiveMethod.
I would suggestto make it more explicit:
recursiveMethod(M);
int target_depth = M - 100;
Then the variable 'recursions' can be removed or become local.
The recursiveMethod takes in the maximum recursions to try and updates
the recursions variable to record how many recursions were possible - so:
target_depth = <actual recursions> - 100;
Possibly recursiveMethod could return the actual recursions instead of
using the global variables?
David
-----
This method will be:
47 private static final int M = 1 << 20;
...
121 public long recursiveMethod(int depth) {
123 if (depth == 0) {
124 notifyAgentToGetLocalAndWaitShortly(M - 100,
waitTimeInNativeAfterNotify);
126 } else {
127 recursiveMethod(--depth);
128 }
129 }
At least, he test is missing the comments explaining all these.
Thanks,
Serguei
On 8/9/20 22:35, David Holmes wrote:
Hi Richard,
On 31/07/2020 5:28 pm, Reingruber, Richard wrote:
Hi,
I rebase the fix after JDK-8250042.
New webrev: http://cr.openjdk.java.net/~rrich/webrevs/8249293/webrev.2/
The general fix for this seems good. A minor nit:
588 if (!is_assignable(signature, ob_k, Thread::current())) {
You know that the current thread is the VMThread so can use
VMThread::vm_thread().
Similarly for this existing code:
694 Thread* current_thread = Thread::current();
---
Looking at the test code ... I'm less clear on exactly what is
happening and the use of spin-waits raises some red-flags for me in
terms of test reliability on different platforms. The "while
(--waitCycles > 0)" loop in particular offers no certainty that the
agent thread is executing anything in particular. And the use of the
spin_count as a guide to future waiting time seems somewhat arbitrary.
In all seriousness I got a headache trying to work out how the test
was expecting to operate. Some parts could be simplified using raw
monitors, I think. But there's no sure way to know the agent thread is
in the midst of the stackwalk when the target thread wants to leave
the native code. So I understand what you are trying to achieve here,
I'm just not sure how reliably it will actually achieve it.
test/hotspot/jtreg/serviceability/jvmti/GetLocalVariable/libGetLocalWithoutSuspendTest.cpp
32 static volatile jlong spinn_count = 0;
Using a 64-bit counter seems like it will be a problem on 32-bit systems.
Should be spin_count not spinn_count.
36 // Agent thread waits for value != 0, then performas the JVMTI
call to get local variable.
typo: performas
Thanks,
David
-----
Thanks, Richard.
-----Original Message-----
From: serviceability-dev <[email protected]>
On Behalf Of Reingruber, Richard
Sent: Montag, 27. Juli 2020 09:45
To: [email protected]; [email protected]
Subject: [CAUTION] RE: RFR(S) 8249293: Unsafe stackwalk in
VM_GetOrSetLocal::doit_prologue()
Hi Serguei,
> I tested it on Linux and Windows but not yet on MacOS.
The test succeeded now on all platforms.
Thanks, Richard.
-----Original Message-----
From: Reingruber, Richard
Sent: Freitag, 24. Juli 2020 15:04
To: [email protected]; [email protected]
Subject: RE: RFR(S) 8249293: Unsafe stackwalk in
VM_GetOrSetLocal::doit_prologue()
Hi Serguei,
The fix itself looks good to me.
thanks for looking at the fix.
I still need another look at new test.
Could you, please, convert the agent of new test to C++?
It will make it a little bit simpler.
Sure, here is the new webrev.1 with a C++ version of the test agent:
http://cr.openjdk.java.net/~rrich/webrevs/8249293/webrev.1/
I tested it on Linux and Windows but not yet on MacOS.
Thanks,
Richard.
-----Original Message-----
From: [email protected] <[email protected]>
Sent: Freitag, 24. Juli 2020 00:00
To: Reingruber, Richard <[email protected]>;
[email protected]
Subject: Re: RFR(S) 8249293: Unsafe stackwalk in
VM_GetOrSetLocal::doit_prologue()
Hi Richard,
Thank you for filing the CR and taking care about it!
The fix itself looks good to me.
I still need another look at new test.
Could you, please, convert the agent of new test to C++?
It will make it a little bit simpler.
Thanks,
Serguei
On 7/20/20 01:15, Reingruber, Richard wrote:
Hi,
please help review this fix for VM_GetOrSetLocal. It moves the
unsafe stackwalk from the vm
operation prologue before the safepoint into the doit() method
executed at the safepoint.
Webrev:
http://cr.openjdk.java.net/~rrich/webrevs/8249293/webrev.0/index.html
Bug: https://bugs.openjdk.java.net/browse/JDK-8249293
According to the JVMTI spec on local variable access it is not
required to suspend the target thread
T [1]. The operation will simply fail with
JVMTI_ERROR_NO_MORE_FRAMES if T is executing
bytecodes. It will succeed though if T is blocked because of
synchronization or executing some native
code.
The issue is that in the latter case the stack walk in
VM_GetOrSetLocal::doit_prologue() to prepare
the access to the local variable is unsafe, because it is done
before the safepoint and it races
with T returning to execute bytecodes making its stack not walkable.
The included test shows that
this can crash the VM if T wins the race.
Manual testing:
- new test
test/hotspot/jtreg/serviceability/jvmti/GetLocalVariable/GetLocalWithoutSuspendTest.java
- test/hotspot/jtreg/vmTestbase/nsk/jvmti
- test/hotspot/jtreg/serviceability/jvmti
Nightly regression tests @SAP: JCK and JTREG, also in Xcomp mode,
SPECjvm2008, SPECjbb2015,
Renaissance Suite, SAP specific tests with fastdebug and release
builds on all platforms
Thanks, Richard.
[1]
https://docs.oracle.com/en/java/javase/14/docs/specs/jvmti.html#local
