1 #include <linux/context_tracking.h> 2 #include <linux/rcupdate.h> 3 #include <linux/sched.h> 4 #include <linux/percpu.h> 5 #include <linux/hardirq.h> 6 7 struct context_tracking { 8 /* 9 * When active is false, hooks are not set to 10 * minimize overhead: TIF flags are cleared 11 * and calls to user_enter/exit are ignored. This 12 * may be further optimized using static keys. 13 */ 14 bool active; 15 enum { 16 IN_KERNEL = 0, 17 IN_USER, 18 } state; 19 }; 20 21 static DEFINE_PER_CPU(struct context_tracking, context_tracking) = { 22 #ifdef CONFIG_CONTEXT_TRACKING_FORCE 23 .active = true, 24 #endif 25 }; 26 27 void user_enter(void) 28 { 29 unsigned long flags; 30 31 /* 32 * Some contexts may involve an exception occuring in an irq, 33 * leading to that nesting: 34 * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit() 35 * This would mess up the dyntick_nesting count though. And rcu_irq_*() 36 * helpers are enough to protect RCU uses inside the exception. So 37 * just return immediately if we detect we are in an IRQ. 38 */ 39 if (in_interrupt()) 40 return; 41 42 WARN_ON_ONCE(!current->mm); 43 44 local_irq_save(flags); 45 if (__this_cpu_read(context_tracking.active) && 46 __this_cpu_read(context_tracking.state) != IN_USER) { 47 __this_cpu_write(context_tracking.state, IN_USER); 48 rcu_user_enter(); 49 } 50 local_irq_restore(flags); 51 } 52 53 void user_exit(void) 54 { 55 unsigned long flags; 56 57 /* 58 * Some contexts may involve an exception occuring in an irq, 59 * leading to that nesting: 60 * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit() 61 * This would mess up the dyntick_nesting count though. And rcu_irq_*() 62 * helpers are enough to protect RCU uses inside the exception. So 63 * just return immediately if we detect we are in an IRQ. 64 */ 65 if (in_interrupt()) 66 return; 67 68 local_irq_save(flags); 69 if (__this_cpu_read(context_tracking.state) == IN_USER) { 70 __this_cpu_write(context_tracking.state, IN_KERNEL); 71 rcu_user_exit(); 72 } 73 local_irq_restore(flags); 74 } 75 76 void context_tracking_task_switch(struct task_struct *prev, 77 struct task_struct *next) 78 { 79 if (__this_cpu_read(context_tracking.active)) { 80 clear_tsk_thread_flag(prev, TIF_NOHZ); 81 set_tsk_thread_flag(next, TIF_NOHZ); 82 } 83 } 84