lib/smp_processor_id.c

   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 unsigned int debug_smp_processor_id(void)
  11 {
  12         unsigned long preempt_count = preempt_count();
  13         int this_cpu = raw_smp_processor_id();
  14         cpumask_t this_mask;
  15
  16         if (likely(preempt_count))
  17                 goto out;
  18
  19         if (irqs_disabled())
  20                 goto out;
  21
  22         /*
  23          * Kernel threads bound to a single CPU can safely use
  24          * smp_processor_id():
  25          */
  26         this_mask = cpumask_of_cpu(this_cpu);
  27
  28         if (cpus_equal(current->cpus_allowed, this_mask))
  29                 goto out;
  30
  31         /*
  32          * It is valid to assume CPU-locality during early bootup:
  33          */
  34         if (system_state != SYSTEM_RUNNING)
  35                 goto out;
  36
  37         /*
  38          * Avoid recursion:
  39          */
  40         preempt_disable();
  41
  42         if (!printk_ratelimit())
  43                 goto out_enable;
  44
  45         printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] "
  46                         "code: %s/%d\n",
  47                         preempt_count() - 1, current->comm, current->pid);
  48         print_symbol("caller is %s\n", (long)__builtin_return_address(0));
  49         dump_stack();
  50
  51 out_enable:
  52         preempt_enable_no_resched();
  53 out:
  54         return this_cpu;
  55 }
  56
  57 EXPORT_SYMBOL(debug_smp_processor_id);
  58