diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/signal.c | 33 |
1 files changed, 28 insertions, 5 deletions
diff --git a/kernel/signal.c b/kernel/signal.c index 09019017d669..f2a5578326ad 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2329,15 +2329,38 @@ static int ptrace_stop(int exit_code, int why, unsigned long message, do_notify_parent_cldstop(current, false, why); /* - * Don't want to allow preemption here, because - * sys_ptrace() needs this task to be inactive. + * The previous do_notify_parent_cldstop() invocation woke ptracer. + * One a PREEMPTION kernel this can result in preemption requirement + * which will be fulfilled after read_unlock() and the ptracer will be + * put on the CPU. + * The ptracer is in wait_task_inactive(, __TASK_TRACED) waiting for + * this task wait in schedule(). If this task gets preempted then it + * remains enqueued on the runqueue. The ptracer will observe this and + * then sleep for a delay of one HZ tick. In the meantime this task + * gets scheduled, enters schedule() and will wait for the ptracer. * - * XXX: implement read_unlock_no_resched(). + * This preemption point is not bad from a correctness point of + * view but extends the runtime by one HZ tick time due to the + * ptracer's sleep. The preempt-disable section ensures that there + * will be no preemption between unlock and schedule() and so + * improving the performance since the ptracer will observe that + * the tracee is scheduled out once it gets on the CPU. + * + * On PREEMPT_RT locking tasklist_lock does not disable preemption. + * Therefore the task can be preempted after do_notify_parent_cldstop() + * before unlocking tasklist_lock so there is no benefit in doing this. + * + * In fact disabling preemption is harmful on PREEMPT_RT because + * the spinlock_t in cgroup_enter_frozen() must not be acquired + * with preemption disabled due to the 'sleeping' spinlock + * substitution of RT. */ - preempt_disable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_disable(); read_unlock(&tasklist_lock); cgroup_enter_frozen(); - preempt_enable_no_resched(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_enable_no_resched(); schedule(); cgroup_leave_frozen(true); |