From: arighi <arighi@38d2e660-2303-0410-9eaa-f027e97ec537>
Date: Wed, 29 Sep 2010 12:50:16 +0000 (+0000)
Subject: cpu: enforce a memory barrier inside cpu_relax()
X-Git-Tag: 2.6.0~57
X-Git-Url: https://codewiz.org/gitweb?a=commitdiff_plain;h=52c7785bca06ce9a837ac378662f351235ec10a7;p=bertos.git

cpu: enforce a memory barrier inside cpu_relax()

Put a memory barrier inside cpu_relax() to make sure the compiler
doesn't cache variables used outside cpu_relax() in registers.

Suppose to have the following case (used in many device drivers):

static int done = false;

void irq_handler(void)
{
	done = true;
}

void wait_for_completion(void)
{
	while (done == false)
		cpu_relax();
}

If cpu_relax() is just considered a nop the compiler may decide to not
reload the value in the variable "done" from memory, causing a
neverending loop.

The presence of an explicit memory barrier fixes this case.

git-svn-id: https://src.develer.com/svnoss/bertos/trunk@4344 38d2e660-2303-0410-9eaa-f027e97ec537
---

diff --git a/bertos/cpu/power.h b/bertos/cpu/power.h
index 4e88def1..f161c698 100644
--- a/bertos/cpu/power.h
+++ b/bertos/cpu/power.h
@@ -68,6 +68,7 @@
  */
 INLINE void cpu_relax(void)
 {
+	MEMORY_BARRIER;
 #if CONFIG_KERN
 	if (proc_preemptAllowed())
 		proc_yield();