smp_processor_id.c

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/*
 * lib/smp_processor_id.c
 *
 * DEBUG_PREEMPT variant of smp_processor_id().
 */
#include <linux/export.h>
#include <linux/kallsyms.h>
#include <linux/sched.h>

notrace unsigned int debug_smp_processor_id(void)
{
    unsigned long preempt_count = preempt_count();
    int this_cpu = raw_smp_processor_id();

    if (likely(preempt_count))
        goto out;

    if (irqs_disabled())
        goto out;

    /*
     * Kernel threads bound to a single CPU can safely use
     * smp_processor_id():
     */
    if (cpumask_equal(tsk_cpus_allowed(current), cpumask_of(this_cpu)))
        goto out;

    /*
     * It is valid to assume CPU-locality during early bootup:
     */
    if (system_state != SYSTEM_RUNNING)
        goto out;

    /*
     * Avoid recursion:
     */
    preempt_disable_notrace();

    if (!printk_ratelimit())
        goto out_enable;

    printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] "
            "code: %s/%d\n",
            preempt_count() - 1, current->comm, current->pid);
    print_symbol("caller is %s\n", (long)__builtin_return_address(0));
    dump_stack();

out_enable:
    preempt_enable_no_resched_notrace();
out:
    return this_cpu;
}

EXPORT_SYMBOL(debug_smp_processor_id);