On Tue, 12 Jul 2022 22:39:36 GMT, Ioi Lam <ik...@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. > > Ioi Lam has updated the pull request incrementally with two additional > commits since the last revision: > > - add errno to log > - added debug log and tweaked comment
LGTM. My manual tests of this work as expected as well. $ podman run --rm -ti --userns=keep-id -u $(id -u) -v $(pwd)/shared-tmp:/tmp:z -v /disk/openjdk/upstream-sources/git/jdk-jdk/build/linux-x86_64-server-release/images/jdk:/opt/jdk:z -v $(pwd)/test:/opt/test:z fedora:36 /opt/jdk/bin/java -Xlog:perf+memops=debug -cp /opt/test HelloWait [0.001s][debug][perf,memops] PerfDataMemorySize = 32768, os::vm_allocation_granularity = 4096, adjusted size = 32768 [0.001s][info ][perf,memops] Trying to open /tmp/hsperfdata_sgehwolf/1 [0.001s][info ][perf,memops] Successfully opened [0.001s][debug][perf,memops] PerfMemory created: address = 0x00007fac290dd000, size = 32768 Hello! $ podman run --rm -ti --userns=keep-id -u $(id -u) -v $(pwd)/shared-tmp:/tmp:z -v /disk/openjdk/upstream-sources/git/jdk-jdk/build/linux-x86_64-server-release/images/jdk:/opt/jdk:z -v $(pwd)/test:/opt/test:z fedora:36 /opt/jdk/bin/java -Xlog:perf+memops=debug -cp /opt/test HelloWait [0.001s][debug][perf,memops] PerfDataMemorySize = 32768, os::vm_allocation_granularity = 4096, adjusted size = 32768 [0.001s][debug][perf,memops] flock for stale file check failed for /tmp/hsperfdata_sgehwolf/1 [0.001s][info ][perf,memops] Trying to open /tmp/hsperfdata_sgehwolf/1 [0.001s][warning][perf,memops] Cannot use file /tmp/hsperfdata_sgehwolf/1 because it is locked by another process (errno = 11) [0.001s][debug ][perf,memops] PerfMemory created: address = 0x00007fc60bc79000, size = 32768 Hello! ------------- Marked as reviewed by sgehwolf (Reviewer). PR: https://git.openjdk.org/jdk/pull/9406
