--- zzzz-none-000/linux-3.10.107/kernel/context_tracking.c 2017-06-27 09:49:32.000000000 +0000 +++ scorpion-7490-727/linux-3.10.107/kernel/context_tracking.c 2021-02-04 17:41:59.000000000 +0000 @@ -19,23 +19,89 @@ #include #include #include +#include -DEFINE_PER_CPU(struct context_tracking, context_tracking) = { -#ifdef CONFIG_CONTEXT_TRACKING_FORCE - .active = true, -#endif -}; +#define CREATE_TRACE_POINTS +#include + +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); + +static bool context_tracking_recursion_enter(void) +{ + int recursion; + + recursion = __this_cpu_inc_return(context_tracking.recursion); + if (recursion == 1) + return true; + + WARN_ONCE((recursion < 1), "Invalid context tracking recursion value %d\n", recursion); + __this_cpu_dec(context_tracking.recursion); + + return false; +} + +static void context_tracking_recursion_exit(void) +{ + __this_cpu_dec(context_tracking.recursion); +} /** - * user_enter - Inform the context tracking that the CPU is going to - * enter userspace mode. + * 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 userspace, 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. + * 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 user_enter(void) +void __context_tracking_enter(enum ctx_state state) +{ + /* Kernel threads aren't supposed to go to userspace */ + WARN_ON_ONCE(!current->mm); + + if (!context_tracking_recursion_enter()) + return; + + 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); + } + context_tracking_recursion_exit(); +} +NOKPROBE_SYMBOL(__context_tracking_enter); +EXPORT_SYMBOL_GPL(__context_tracking_enter); + +void context_tracking_enter(enum ctx_state state) { unsigned long flags; @@ -50,79 +116,56 @@ 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.active) && - __this_cpu_read(context_tracking.state) != IN_USER) { - /* - * 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. - */ - vtime_user_enter(current); - rcu_user_enter(); - __this_cpu_write(context_tracking.state, IN_USER); - } + __context_tracking_enter(state); local_irq_restore(flags); } +NOKPROBE_SYMBOL(context_tracking_enter); +EXPORT_SYMBOL_GPL(context_tracking_enter); -#ifdef CONFIG_PREEMPT -/** - * preempt_schedule_context - preempt_schedule called by tracing - * - * The tracing infrastructure uses preempt_enable_notrace to prevent - * recursion and tracing preempt enabling caused by the tracing - * infrastructure itself. But as tracing can happen in areas coming - * from userspace or just about to enter userspace, a preempt enable - * can occur before user_exit() is called. This will cause the scheduler - * to be called when the system is still in usermode. - * - * To prevent this, the preempt_enable_notrace will use this function - * instead of preempt_schedule() to exit user context if needed before - * calling the scheduler. - */ -void __sched notrace preempt_schedule_context(void) +void context_tracking_user_enter(void) { - struct thread_info *ti = current_thread_info(); - enum ctx_state prev_ctx; - - if (likely(ti->preempt_count || irqs_disabled())) - return; - - /* - * Need to disable preemption in case user_exit() is traced - * and the tracer calls preempt_enable_notrace() causing - * an infinite recursion. - */ - preempt_disable_notrace(); - prev_ctx = exception_enter(); - preempt_enable_no_resched_notrace(); - - preempt_schedule(); - - preempt_disable_notrace(); - exception_exit(prev_ctx); - preempt_enable_notrace(); + user_enter(); } -EXPORT_SYMBOL_GPL(preempt_schedule_context); -#endif /* CONFIG_PREEMPT */ +NOKPROBE_SYMBOL(context_tracking_user_enter); /** - * user_exit - Inform the context tracking that the CPU is - * exiting userspace mode and entering the kernel. + * 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 userspace - * before any use of RCU read side critical section. This potentially include - * any high level kernel code like syscalls, exceptions, signal handling, etc... + * 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 user_exit(void) +void __context_tracking_exit(enum ctx_state state) +{ + if (!context_tracking_recursion_enter()) + return; + + 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); + } + context_tracking_recursion_exit(); +} +NOKPROBE_SYMBOL(__context_tracking_exit); +EXPORT_SYMBOL_GPL(__context_tracking_exit); + +void context_tracking_exit(enum ctx_state state) { unsigned long flags; @@ -130,55 +173,46 @@ return; local_irq_save(flags); - if (__this_cpu_read(context_tracking.state) == IN_USER) { - /* - * 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(); - vtime_user_exit(current); - __this_cpu_write(context_tracking.state, IN_KERNEL); - } + __context_tracking_exit(state); local_irq_restore(flags); } +NOKPROBE_SYMBOL(context_tracking_exit); +EXPORT_SYMBOL_GPL(context_tracking_exit); -void guest_enter(void) +void context_tracking_user_exit(void) { - if (vtime_accounting_enabled()) - vtime_guest_enter(current); - else - __guest_enter(); + user_exit(); } -EXPORT_SYMBOL_GPL(guest_enter); +NOKPROBE_SYMBOL(context_tracking_user_exit); -void guest_exit(void) +void __init context_tracking_cpu_set(int cpu) { - if (vtime_accounting_enabled()) - vtime_guest_exit(current); - else - __guest_exit(); -} -EXPORT_SYMBOL_GPL(guest_exit); + static __initdata bool initialized = false; + if (!per_cpu(context_tracking.active, cpu)) { + per_cpu(context_tracking.active, cpu) = true; + static_key_slow_inc(&context_tracking_enabled); + } -/** - * 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) + if (initialized) + return; + + /* + * Set TIF_NOHZ to init/0 and let it propagate to all tasks through fork + * This assumes that init is the only task at this early boot stage. + */ + set_tsk_thread_flag(&init_task, TIF_NOHZ); + WARN_ON_ONCE(!tasklist_empty()); + + initialized = true; +} + +#ifdef CONFIG_CONTEXT_TRACKING_FORCE +void __init context_tracking_init(void) { - if (__this_cpu_read(context_tracking.active)) { - clear_tsk_thread_flag(prev, TIF_NOHZ); - set_tsk_thread_flag(next, TIF_NOHZ); - } + int cpu; + + for_each_possible_cpu(cpu) + context_tracking_cpu_set(cpu); } +#endif