* Christoph Lameter <cl@xxxxxxxxx> wrote:
> Index: linux/lib/smp_processor_id.c
> ===================================================================
> --- linux.orig/lib/smp_processor_id.c 2013-09-24 10:06:26.000000000 -0500
> +++ linux/lib/smp_processor_id.c 2013-09-24 10:14:19.412825970 -0500
> @@ -7,7 +7,7 @@
> #include <linux/kallsyms.h>
> #include <linux/sched.h>
>
> -notrace unsigned int debug_smp_processor_id(void)
> +notrace static unsigned int check_preemption(char *what)
> {
> unsigned long preempt_count = preempt_count();
> int this_cpu = raw_smp_processor_id();
> @@ -39,8 +39,8 @@ notrace unsigned int debug_smp_processor
> if (!printk_ratelimit())
> goto out_enable;
>
> - printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] "
> - "code: %s/%d\n",
> + printk(KERN_ERR "BUG: using %s in preemptible [%08x] "
> + "code: %s/%d\n", what,
> preempt_count() - 1, current->comm, current->pid);
> print_symbol("caller is %s\n", (long)__builtin_return_address(0));
> dump_stack();
> @@ -51,5 +51,18 @@ out:
> return this_cpu;
> }
>
> +notrace unsigned int debug_smp_processor_id(void)
> +{
> + return check_preemption("smp_processor_id()");
> +
> +}
> EXPORT_SYMBOL(debug_smp_processor_id);
>
> +notrace void __this_cpu_preempt_check(void)
> +{
> +#ifdef CONFIG_THIS_CPU_PREEMPTION_CHECK
> + check_preemption("__this_cpu operation");
> +#endif
> +}
> +EXPORT_SYMBOL(__this_cpu_preempt_check);
Ok, this variant looks pretty good, modulo testing. I'd do:
s/check_preemption/check_preemption_disabled
but that's a minor detail.
> +config DEBUG_THIS_CPU_OPERATIONS
> + bool "Debug __this_cpu operations"
> + depends on DEBUG_PREEMPT
> + default n
> + help
> + Enables preemption checks for __this_cpu macros. These
> + are macros to generate single instruction operations on
> + per cpu data. The option only affects the __this_cpu variant
> + which is used when fallback to multiple instructions without
> + other synchronization is possible. A verification is then
> + done to make sure that the thread cannot be preempted.
I don't think there's a need to make this a separate preemption debug
option: smp_processor_id() is really just a subset of the checks.
So please just put it under CONFIG_DEBUG_PREEMPT, there's no need to add
yet another x2 to the kernel Kconfig space. Maybe extend the DEBUG_PREEMPT
help text to explain that it also checks __this_cpu ops.
That will remove the #ifdef from lib/smp_processor_id.c and will simplify
debugging a bit as well.
Thanks,
Ingo
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