cf-natali commented on a change in pull request #355: Handle EBUSY when
destroying a cgroup.
URL: https://github.com/apache/mesos/pull/355#discussion_r402382128
##########
File path: src/linux/cgroups.cpp
##########
@@ -696,13 +696,24 @@ Try<Nothing> remove(const string& hierarchy, const
string& cgroup)
string path = path::join(hierarchy, cgroup);
// Do NOT recursively remove cgroups.
- Try<Nothing> rmdir = os::rmdir(path, false);
- if (rmdir.isError()) {
- return Error(
+ // TODO The retry was added as a fix for kernel bug
+ // https://lkml.org/lkml/2020/1/15/1349
+ // where calling rmdir on a seemingly empty cgroup can fail
+ // with EBUSY while some tasks are exiting.
+ auto delay = Milliseconds(1);
+ for (auto retry = 10; ;) {
+ Try<Nothing> rmdir = os::rmdir(path, false);
+ if (!rmdir.isError()) {
+ return rmdir;
+ } else if (retry > 0) {
+ os::sleep(delay);
Review comment:
> XfsDiskIsolatorProcess::initialize and IOSwitchboard::_connect are
examples of how process::loop() can be used to implement non-blocking retries.
> The new remove function can be used in both places you have mentioned
above where the blocking cgroups::remove function is called.
Sorry, I don't really see how to do this in a helper function: the problem
is that we need to persist state from one call to the next - e.g. the delay and
current retry count - and we don't have a scope where those variables would be
live.
For example if the function looked like:
```
Future<Nothing> remove(const std::string& hierarchy, const std::string&
cgroup)
{
const auto path = path::join(hierarchy, cgroup);
auto delay = Milliseconds(1);
auto retry = 10;
auto result = Future<Nothing>();
return loop(
[&]() {
return process::after(delay);
},
[&](const Nothing&) -> ControlFlow<Nothing> {
if (::rmdir(path.c_str()) == 0) {
return process::Break();
} else if ((errno == EBUSY) && (retry > 0)) {
delay *= 2;
--retry;
return process::Continue();
} else {
// If the `cgroup` still exists in the hierarchy, treat this as
// an error; otherwise, treat this as a success since the `cgroup`
// has actually been cleaned up.
if (os::exists(path::join(hierarchy, cgroup))) {
result = Failure(
"Failed to remove directory '" + path + "': " +
os::strerror(errno));
}
return process::Break();
}
}
);
return result;
}
```
The `delay`, `retry` and `result` would be reference to local variables, so
invalid.
`XfsDiskIsolatorProcess::initialize` and `IOSwitchboard::_connect` are both
member functions of the processes on bahalf of which they're run, so don't have
this problem.
TBH I'm not really familiar with libprocess, maybe it would be much easier
for you to write the patch?
----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
For queries about this service, please contact Infrastructure at:
[email protected]
With regards,
Apache Git Services
