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Subject [GitHub] [mesos] cf-natali commented on a change in pull request #355: Handle EBUSY when destroying a cgroup.
Date Tue, 07 Apr 2020 18:21:03 GMT
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_r405018860
 
 

 ##########
 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:
   Hm, I'm still confused: in your version, you capture `retry` and `delay` in the lambdas
by value, so their modifications are lost:
   
   ```
     return loop(
         // NOTE: copy `delay` by value in the first lambda function.
         [=]() mutable {
           auto timeout = process::after(delay);
           delay *= 2;
           return timeout;
         },
         // NOTE: copy `retry` by value in the second lambda function.
         [=](const Nothing&) mutable -> Future<ControlFlow<Nothing>> {
   [...]
           } else if ((errno == EBUSY) && (retry > 0)) {
             --retry;
             return process::Continue();
   ```
   
   I think that with this, `delay` and `retry` will *not* be updated from one iteration to
the next: so basically we will keep retrying the `rmdir` every ms forever.

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