[LU-12640] per cpu env race

• Type: Bug
• Resolution: Cannot Reproduce
• Priority: Minor
• Severity: 3
• Assignee: Wang Shilong (Inactive)
• Reporter: Wang Shilong (Inactive)

Description

The checking and assgin below could be racy:

    if (lu_env_percpu[i].lep_task == current) {
            env = lu_env_percpu[i].lep_env;
    
    CPU0
      thread0 lu_env_percpu[i].lep_task == current
         thread1 switch into CPU0 changes lu_env_percpu[0]
           thread0 switch back CPU0,return lu_env_percpu[0].lep_env;
    

The problem is access and change per_cpu variable here
shall be atomic, since it is per cpu variable, we should
take care it not been preempted.