Bug ID: JDK-8179954 AArch64: C1 and C2 volatile accesses are not sequentially consistent

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JDK 10	JDK 8	JDK 9	Other
10Fixed	8u371Fixed	9 b170Fixed	openjdk8u292Fixed

In C2 we use LDAR/STLR to handle volatile accesses, but  in C1 and the interpreter we use separate DMB instructions and relaxed loads. When used together, these do not form a sequentially-consistent memory ordering. For example, if stores use STLR and loads use LDR;DMB a simple Dekker idiom will fail.

This is extremely hard to test because the loads and stores have to be in separately-compiled methods, but it is incorrect, and likely to fail in very weakly-ordered implementations.

Thanks for your attention. Looks like I should send a mail to aarch64-port mailing list requesting for approval.
31-07-2019
There is no AArch64 port in jdk8u at present.
30-07-2019
Fix Request 8u
26-07-2019
URL: http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/38a240fd58a2 User: lana Date: 2017-05-17 18:48:03 +0000
17-05-2017
Seems like this was pushed to JDK 9 without approval. [~aph], please add the request according to [1]. [1] http://openjdk.java.net/projects/jdk9/fix-request-process
16-05-2017
URL: http://hg.openjdk.java.net/jdk9/dev/hotspot/rev/38a240fd58a2 User: aph Date: 2017-05-16 17:31:49 +0000
16-05-2017
Please, add fix request comment and label according to RDP 2 process if you target JDK 9.
16-05-2017
The code is Thread 1 \| Thread 2 x = 1 \| y = 1 r1 = y \| r1 = x The commits to x and y should be ordered, so it's forbidden for both threads to read 0. The problem is that if we use STLR for the store and LDR;DMB for the load we get STLR #1 -> [x] \| STLR #1 -> [y] LDR [y] -> r1 \| LDR [x] -> r1 DMB \| DMB This can happen if the STLR is emitted by C2 and the LDR;DMB by C1. Obviously the trailing DMB can have no effect, so the result is not sequentially consistent. We want to keep using LDAR and STLR in C2, so the right answer is to fix C1 and the interpreter so that we see STLR #1 -> [x] \| STLR #1 -> [y] DMB \| DMB LDR [y] -> r1 \| LDR [x] -> r1 DMB LD \| DMB LD
11-05-2017

Relates :	JDK-8257192 - Integrate AArch64 JIT port into 8u
Relates :	JDK-8241137 - AArch64: Volatile accesses are not sequentially consistent with VM option "-XX:+UseBarriersForVolatile"