Bug #87293 TTASFutex Lock release barrier (aarch64)

• Submitted: 3 Aug 2017 5:49
• Modified: 10 Oct 2017 16:51
• Reporter: Debayan Ghosh (OCA)
• Status: Verified
• Category: MySQL Server: InnoDB storage engine
• Severity: S2 (Serious)
• Version: 5.7, 8.0
• OS: Linux
• CPU Architecture: ARM
• Tags: aarch64, barriers, Contribution

[3 Aug 2017 5:49] Debayan Ghosh

Description:
The TTASFutexMutex implementation for lock release uses a os_rmb() which may not
guarantee the changes to locked data structures are made observable before the unlock becomes observable.

This causes a mysql server hang on aarch64 platforms when tested with sysbench oltp workloads at higher threads (>64T)

How to repeat:

Compile mysql-server with DMUTEXTYPE=futex

Run sysbench 1.1.0 oltp_update_index/oltp_write_only test with 64 threads and more.

Suggested fix:
Suggest to use a ATOMIC_RELEASE in place of ATOMIC_ACQUIRE i.e use os_wmb instead of os_rmb in the code.

This also fixes the runtime issue.

[4 Aug 2017 2:25] Debayan Ghosh

Changed category to InnoDB Storage Engine.

[24 Aug 2017 1:51] Debayan Ghosh

memory barrier change

(*) I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Contribution: 0001-Fix-barrier-for-FutexMutex-lock-exit-implementation.patch (application/octet-stream, text), 796 bytes.

[29 Aug 2017 5:08] MySQL Verification Team

Hello Debayan,

Thank you for the report and contribution.

Thanks,
Umesh

[10 Oct 2017 16:51] Debayan Ghosh

This crash issue is reproduced with mysql-8.0.3 tag as well on Aarch64 platform.
The suggested barrier change fixes it.