linux-kernel - Re: [linux-next][regression] [PATCH] percpu: add preemption checks to __this

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Date:	Tue, 18 Mar 2014 10:54:06 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Grygorii Strashko <grygorii.strashko@...com>
cc:	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [linux-next][regression] [PATCH] percpu: add preemption checks
 to __this_cpu ops

On Tue, 18 Mar 2014, Grygorii Strashko wrote:

> Any way, I can boot and console works fine with your change :)
> Thanks.

Ok here is the properly formatted patch:


Subject: preemption_checks: Avoid snprintf before checking error conditions

snprintf can cause hangs. Move the string processing into the function
so that the string operations only occur when necessary after the
conditions have been checked.

Tested-by: Grygorii Strashko <grygorii.strashko@...com>
Signed-off-by: Christoph Lameter <cl@...ux.com>



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);
--
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