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[Serge Hallyn <1341364@xxxxxxxxxxxxxxxxxx>]

This appears to be fixed in http://kernel.ubuntu.com/~kernel-
ppa/mainline/v3.16-rc5-utopic/

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https://bugs.launchpad.net/bugs/1341364

Title:
  cgroupfs rmdir race (regression)

Status in “linux” package in Ubuntu:
  Triaged

Bug description:
  In older utopic kernels (abi-3.15.0-6-generic), when I quickly rmdir
  /a/b and then rmdir /a, it succeeds.  With the kernel in utopic, the
  rmdir of cgroup /a fails with EBUSY.  This appears to be a race.

  The following test program quite reliably shows the race:

  #include <stdio.h>                                         
  #include <stdlib.h>                                           
  #include <sys/stat.h>
  #include <sys/types.h>
  #include <sys/mount.h>
  #include <errno.h>
  #include <string.h>
   
  int main()
  {
          int ret;
          int i;
          char path[1024], f[30];

          ret = mount("cgroup", "/mnt", "cgroup", 0, "memory");
          if (ret) {
                  perror("mount");
                  exit(1);
          }
                
          sprintf(path, "/mnt");
          printf("creating\n");
          for (i = 0; i < 10; i++) {
                  sprintf(f, "/dir%d", i);
                  strcat(path, f);
                  ret = mkdir(path, 0755);
                  if (ret && errno != EEXIST) {
                          perror("mkdir");
                          printf("Failed on %d\n", i);
                          umount("/mnt");
                          exit(1);
                  }
          }                                      
          printf("Now removing\n");                      
          for (i = 9;  i >= 0;  i--) {                                        
                  ret = rmdir(path);
                  if (ret) {                               
                          perror("rmdir");                         
                          printf("Failed removing %s\n", path);
                          umount("/mnt");
                          exit(1);
                  }
                  char *p = strrchr(path, '/');
                  *p = '\0';
          }                            
          umount("/mnt");                      
          printf("Done - success\n");
  }                                  

  This is also blocking promotion of the cgmanager package to utopic due
  to jenkins failure:

  
  https://jenkins.qa.ubuntu.com/job/utopic-adt-cgmanager/30/ARCH=amd64,label=adt/console

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