/** * context_tracking_exit - Inform the context tracking that the CPU is * exiting user or guest mode and entering the kernel. * * This function must be called after we entered the kernel from user or * guest space before any use of RCU read side critical section. This * potentially include any high level kernel code like syscalls, exceptions, * signal handling, etc... * * This call supports re-entrancy. This way it can be called from any exception * handler without needing to know if we came from userspace or not. */ void context_tracking_exit(enum ctx_state state) { unsigned long flags; if (!context_tracking_is_enabled()) return; if (in_interrupt()) return; local_irq_save(flags); if (__this_cpu_read(context_tracking.state) == state) { if (__this_cpu_read(context_tracking.active)) { /* * We are going to run code that may use RCU. Inform * RCU core about that (ie: we may need the tick again). */ rcu_user_exit(); if (state == CONTEXT_USER) { vtime_user_exit(current); trace_user_exit(0); } } __this_cpu_write(context_tracking.state, CONTEXT_KERNEL); } local_irq_restore(flags); }
/** * context_tracking_enter - Inform the context tracking that the CPU is going * enter user or guest space mode. * * This function must be called right before we switch from the kernel * to user or guest space, when it's guaranteed the remaining kernel * instructions to execute won't use any RCU read side critical section * because this function sets RCU in extended quiescent state. */ void context_tracking_enter(enum ctx_state state) { unsigned long flags; /* * Repeat the user_enter() check here because some archs may be calling * this from asm and if no CPU needs context tracking, they shouldn't * go further. Repeat the check here until they support the inline static * key check. */ if (!context_tracking_is_enabled()) return; /* * Some contexts may involve an exception occuring in an irq, * leading to that nesting: * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit() * This would mess up the dyntick_nesting count though. And rcu_irq_*() * helpers are enough to protect RCU uses inside the exception. So * just return immediately if we detect we are in an IRQ. */ if (in_interrupt()) return; /* Kernel threads aren't supposed to go to userspace */ WARN_ON_ONCE(!current->mm); local_irq_save(flags); if ( __this_cpu_read(context_tracking.state) != state) { if (__this_cpu_read(context_tracking.active)) { /* * At this stage, only low level arch entry code remains and * then we'll run in userspace. We can assume there won't be * any RCU read-side critical section until the next call to * user_exit() or rcu_irq_enter(). Let's remove RCU's dependency * on the tick. */ if (state == CONTEXT_USER) { trace_user_enter(0); vtime_user_enter(current); } rcu_user_enter(); } /* * Even if context tracking is disabled on this CPU, because it's outside * the full dynticks mask for example, we still have to keep track of the * context transitions and states to prevent inconsistency on those of * other CPUs. * If a task triggers an exception in userspace, sleep on the exception * handler and then migrate to another CPU, that new CPU must know where * the exception returns by the time we call exception_exit(). * This information can only be provided by the previous CPU when it called * exception_enter(). * OTOH we can spare the calls to vtime and RCU when context_tracking.active * is false because we know that CPU is not tickless. */ __this_cpu_write(context_tracking.state, state); } local_irq_restore(flags); }
/* * We need the IPIs to be sent from sane process context. * The posix cpu timers are always set with irqs disabled. */ static void posix_cpu_timer_kick_nohz(void) { if (context_tracking_is_enabled()) schedule_work(&nohz_kick_work); }