context_tracking.c

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    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 }

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FreeBSD/Linux Kernel Cross Reference sys/kernel/context_tracking.c

FreeBSD/Linux Kernel Cross Reference
sys/kernel/context_tracking.c