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SubjectRe: [PATCH 6/6] percpu: Add preemption checks to __this_cpu ops
On Tue, Oct 15, 2013 at 12:47:28PM -0500, Christoph Lameter wrote:
> V3->V4:
> - Drop CONFIG_DEBUG_THIS_CPU_OPERATIONS
> - Add support for logging the exact operation that caused the issue.
>
> We define a check function in order to avoid trouble with the
> include files. Then the higher level __this_cpu macros are
> modified to invoke the check before __this_cpu operation
>
> Signed-off-by: Christoph Lameter <cl@linux.com>
>
> Index: linux/include/linux/percpu.h
> ===================================================================
> --- linux.orig/include/linux/percpu.h 2013-10-10 11:30:17.111743444 -0500
> +++ linux/include/linux/percpu.h 2013-10-10 10:30:26.817316787 -0500
> @@ -175,6 +175,12 @@ extern phys_addr_t per_cpu_ptr_to_phys(v
>
> extern void __bad_size_call_parameter(void);
>
> +#ifdef CONFIG_DEBUG_PREEMPT
> +extern void __this_cpu_preempt_check(const char *op);
> +#else
> +static inline void __this_cpu_preempt_check(const char *op) { }
> +#endif
> +
> #define __pcpu_size_call_return(stem, variable) \
> ({ typeof(variable) pscr_ret__; \
> __verify_pcpu_ptr(&(variable)); \
> @@ -538,7 +544,8 @@ do { \
> # ifndef __this_cpu_read_8
> # define __this_cpu_read_8(pcp) (*__this_cpu_ptr(&(pcp)))
> # endif
> -# define __this_cpu_read(pcp) __pcpu_size_call_return(__this_cpu_read_, (pcp))
> +# define __this_cpu_read(pcp) \
> + (__this_cpu_preempt_check("read"),__pcpu_size_call_return(__this_cpu_read_, (pcp)))
> #endif
>

So I didn't understand what was wrong with:

#define __this_cpu_read(pcp) \
(__this_cpu_preempt_check("read"), raw_this_cpu_read(pcp))

And idem for all others. This is 1) shorter to write; and 2) makes it
blindingly obvious that the implementations are actually the same.

> Index: linux/lib/smp_processor_id.c
> ===================================================================
> --- linux.orig/lib/smp_processor_id.c 2013-10-10 11:30:17.111743444 -0500
> +++ linux/lib/smp_processor_id.c 2013-10-10 10:32:16.046357108 -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_disabled(char *what)
> {
> unsigned long preempt_count = preempt_count();
> int this_cpu = raw_smp_processor_id();
> @@ -39,9 +39,9 @@ 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",
> - preempt_count() - 1, current->comm, current->pid);
> + printk(KERN_ERR "%s in preemptible [%08x] code: %s/%d\n",
> + what, preempt_count() - 1, current->comm, current->pid);
> +

Like already said; NAK until that "BUG" remains.


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