linux/lib/smp_processor_id.c
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   1/*
   2 * lib/smp_processor_id.c
   3 *
   4 * DEBUG_PREEMPT variant of smp_processor_id().
   5 */
   6#include <linux/export.h>
   7#include <linux/kallsyms.h>
   8#include <linux/sched.h>
   9
  10notrace 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 (cpumask_equal(tsk_cpus_allowed(current), cpumask_of(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
  48out_enable:
  49        preempt_enable_no_resched_notrace();
  50out:
  51        return this_cpu;
  52}
  53
  54EXPORT_SYMBOL(debug_smp_processor_id);
  55
  56
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