| /* |
| * Context tracking: Probe on high level context boundaries such as kernel |
| * and userspace. This includes syscalls and exceptions entry/exit. |
| * |
| * This is used by RCU to remove its dependency on the timer tick while a CPU |
| * runs in userspace. |
| * |
| * Started by Frederic Weisbecker: |
| * |
| * Copyright (C) 2012 Red Hat, Inc., Frederic Weisbecker <fweisbec@redhat.com> |
| * |
| * Many thanks to Gilad Ben-Yossef, Paul McKenney, Ingo Molnar, Andrew Morton, |
| * Steven Rostedt, Peter Zijlstra for suggestions and improvements. |
| * |
| */ |
| |
| #include <linux/context_tracking.h> |
| #include <linux/rcupdate.h> |
| #include <linux/sched.h> |
| #include <linux/hardirq.h> |
| #include <linux/export.h> |
| #include <linux/kprobes.h> |
| |
| #define CREATE_TRACE_POINTS |
| #include <trace/events/context_tracking.h> |
| |
| struct static_key context_tracking_enabled = STATIC_KEY_INIT_FALSE; |
| EXPORT_SYMBOL_GPL(context_tracking_enabled); |
| |
| DEFINE_PER_CPU(struct context_tracking, context_tracking); |
| EXPORT_SYMBOL_GPL(context_tracking); |
| |
| void context_tracking_cpu_set(int cpu) |
| { |
| if (!per_cpu(context_tracking.active, cpu)) { |
| per_cpu(context_tracking.active, cpu) = true; |
| static_key_slow_inc(&context_tracking_enabled); |
| } |
| } |
| |
| /** |
| * 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); |
| } |
| NOKPROBE_SYMBOL(context_tracking_enter); |
| EXPORT_SYMBOL_GPL(context_tracking_enter); |
| |
| void context_tracking_user_enter(void) |
| { |
| context_tracking_enter(CONTEXT_USER); |
| } |
| NOKPROBE_SYMBOL(context_tracking_user_enter); |
| |
| /** |
| * 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); |
| } |
| NOKPROBE_SYMBOL(context_tracking_exit); |
| EXPORT_SYMBOL_GPL(context_tracking_exit); |
| |
| void context_tracking_user_exit(void) |
| { |
| context_tracking_exit(CONTEXT_USER); |
| } |
| NOKPROBE_SYMBOL(context_tracking_user_exit); |
| |
| /** |
| * __context_tracking_task_switch - context switch the syscall callbacks |
| * @prev: the task that is being switched out |
| * @next: the task that is being switched in |
| * |
| * The context tracking uses the syscall slow path to implement its user-kernel |
| * boundaries probes on syscalls. This way it doesn't impact the syscall fast |
| * path on CPUs that don't do context tracking. |
| * |
| * But we need to clear the flag on the previous task because it may later |
| * migrate to some CPU that doesn't do the context tracking. As such the TIF |
| * flag may not be desired there. |
| */ |
| void __context_tracking_task_switch(struct task_struct *prev, |
| struct task_struct *next) |
| { |
| clear_tsk_thread_flag(prev, TIF_NOHZ); |
| set_tsk_thread_flag(next, TIF_NOHZ); |
| } |
| |
| #ifdef CONFIG_CONTEXT_TRACKING_FORCE |
| void __init context_tracking_init(void) |
| { |
| int cpu; |
| |
| for_each_possible_cpu(cpu) |
| context_tracking_cpu_set(cpu); |
| } |
| #endif |