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   1 /*
   2  * lib/smp_processor_id.c
   3  *
   4  * DEBUG_PREEMPT variant of smp_processor_id().
   5  */
   6 #include <linux/module.h>
   7 #include <linux/kallsyms.h>
   8 #include <linux/sched.h>
   9
  10 notrace unsigned int debug_smp_processor_id(void)
  11 {
  12         unsigned long preempt_count = preempt_count();
  13         int this_cpu = raw_smp_processor_id();
  14
  15         if (likely(preempt_count))
  16                 goto out;
  17
  18         if (irqs_disabled())
  19                 goto out;
  20
  21         /*
  22          * Kernel threads bound to a single CPU can safely use
  23          * smp_processor_id():
  24          */
  25         if (cpus_equal(current->cpus_allowed, cpumask_of_cpu(this_cpu)))
  26                 goto out;
  27
  28         /*
  29          * It is valid to assume CPU-locality during early bootup:
  30          */
  31         if (system_state != SYSTEM_RUNNING)
  32                 goto out;
  33
  34         /*
  35          * Avoid recursion:
  36          */
  37         preempt_disable_notrace();
  38
  39         if (!printk_ratelimit())
  40                 goto out_enable;
  41
  42         printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] "
  43                         "code: %s/%d\n",
  44                         preempt_count() - 1, current->comm, current->pid);
  45         print_symbol("caller is %s\n", (long)__builtin_return_address(0));
  46         dump_stack();
  47
  48 out_enable:
  49         preempt_enable_no_resched_notrace();
  50 out:
  51         return this_cpu;
  52 }
  53
  54 EXPORT_SYMBOL(debug_smp_processor_id);
  55