Integrated: 8286030: Avoid JVM crash when containers share the same /tmp dir

[Ioi Lam]

On Thu, 7 Jul 2022 06:01:58 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> Some Kubernetes setups share the /tmp directory across multiple containers. On rare occasions, the JVM may crash when it tries to write to `/tmp/hsperfdata_<user>/<pid>` when a process in a separate container decides to do the same thing (because they happen to have the same namespaced pid).
> 
> This patch avoids the crash by using `flock()` to allow only one of these processes to write to the file. All other competing processes that fail to grab the lock will give up the file and run with PerfMemory disabled. We will try to enable PerfMemory for the failed processes in a follow-up RFE: [JDK-8289883](https://bugs.openjdk.org/browse/JDK-8289883)
> 
> Thanks to Vitaly Davidovich and Nico Williams for coming up with the idea of using `flock()`.
> 
> I kept the use of `kill()` for stale file detection to be compatible with older JVMs.
> 
> I also took the opportunity to clean up the comments and remove dead code. The old code was using "shared memory resources" which sounds unclear and odd. I changed the terminology to say "shared memory file" instead.

This pull request has now been integrated.

Changeset: 84f23149
Author:    Ioi Lam <iklam at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/84f23149e22561173feb0e34bca31a7345b43c89
Stats:     324 lines in 3 files changed: 267 ins; 27 del; 30 mod

8286030: Avoid JVM crash when containers share the same /tmp dir

Reviewed-by: stuefe, sgehwolf

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PR: https://git.openjdk.org/jdk/pull/9406