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Oleg Nesterov authored
thread_group_cputime() looks as if it is rcu-safe, but in fact this was wrong until ea6d290c which pins task->signal to task_struct. It checks ->sighand != NULL under rcu, but this can't help if ->signal can go away. Fortunately the caller either holds ->siglock, or it is fastpath_timer_check() which uses current and checks exit_state == 0. - Since ea6d290c commit tsk->signal is stable, we can read it first and avoid the initialization from INIT_CPUTIME. - Even if tsk->signal is always valid, we still have to check it is safe to use next_thread() under rcu_read_lock(). Currently the code checks ->sighand != NULL, change it to use pid_alive() which is commonly used to ensure the task wasn't unhashed before we take rcu_read_lock(). Add the comment to explain this check. - Change the main loop to use the while_each_thread() helper. Signed-off-by:
Oleg Nesterov <oleg@redhat.com> Signed-off-by:
Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20100610230956.GA25921@redhat.com> Signed-off-by:
Ingo Molnar <mingo@elte.hu>
Oleg Nesterov authoredthread_group_cputime() looks as if it is rcu-safe, but in fact this was wrong until ea6d290c which pins task->signal to task_struct. It checks ->sighand != NULL under rcu, but this can't help if ->signal can go away. Fortunately the caller either holds ->siglock, or it is fastpath_timer_check() which uses current and checks exit_state == 0. - Since ea6d290c commit tsk->signal is stable, we can read it first and avoid the initialization from INIT_CPUTIME. - Even if tsk->signal is always valid, we still have to check it is safe to use next_thread() under rcu_read_lock(). Currently the code checks ->sighand != NULL, change it to use pid_alive() which is commonly used to ensure the task wasn't unhashed before we take rcu_read_lock(). Add the comment to explain this check. - Change the main loop to use the while_each_thread() helper. Signed-off-by:
