[linux-next][regression] [PATCH] percpu: add preemption checks to __this_cpu ops

Christoph Lameter
2014-03-18T14:37:58Z

On Tue, 18 Mar 2014, Grygorii Strashko wrote:

> diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
> index a270dce..73a2004 100644
> --- a/lib/smp_processor_id.c
> +++ b/lib/smp_processor_id.c
> @@ -58,9 +58,6 @@ EXPORT_SYMBOL(debug_smp_processor_id);
>
> notrace void __this_cpu_preempt_check(const char *op)
> {
> - char text[40];
> -
> - snprintf(text, sizeof(text), "__this_cpu_%s()", op);
> - check_preemption_disabled(text);
> + check_preemption_disabled(op);
> }
> EXPORT_SYMBOL(__this_cpu_preempt_check);

So it looks like there is an early this cpu operation in a context that
cannot handle snprintf. But the checks in check_preemption_disabled()
avoid processing there so that works.

We could fix this by moving the string concatenation operation into
the check function.

Index: linux/lib/smp_processor_id.c
===================================================================
--- linux.orig/lib/smp_processor_id.c 2014-03-18 09:36:31.330450525 -0500
+++ linux/lib/smp_processor_id.c 2014-03-18 09:36:37.822315534 -0500
@@ -7,7 +7,8 @@
#include <linux/kallsyms.h>
#include <linux/sched.h>

-notrace static unsigned int check_preemption_disabled(char *what)
+notrace static unsigned int check_preemption_disabled(const char *what1,
+ const char *what2)
{
int this_cpu = raw_smp_processor_id();

@@ -38,8 +39,8 @@
if (!printk_ratelimit())
goto out_enable;

- printk(KERN_ERR "BUG: using %s in preemptible [%08x] code: %s/%d\n",
- what, preempt_count() - 1, current->comm, current->pid);
+ printk(KERN_ERR "BUG: using %s%s() in preemptible [%08x] code: %s/%d\n",
+ what1, what2, preempt_count() - 1, current->comm, current->pid);

print_symbol("caller is %s\n", (long)__builtin_return_address(0));
dump_stack();
@@ -52,15 +53,12 @@

notrace unsigned int debug_smp_processor_id(void)
{
- return check_preemption_disabled("smp_processor_id()");
+ return check_preemption_disabled("smp_processor_id","");
}
EXPORT_SYMBOL(debug_smp_processor_id);

notrace void __this_cpu_preempt_check(const char *op)
{
- char text[40];
-
- snprintf(text, sizeof(text), "__this_cpu_%s()", op);
- check_preemption_disabled(text);
+ check_preemption_disabled("__this_cpu_", op);
}
EXPORT_SYMBOL(__this_cpu_preempt_check);