linux-kernel - [PATCH] fault-inject: Avoid call to random32() if fault injection is disabled

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Message-ID: <20120601104925.5135263c@kryten>
Date:	Fri, 1 Jun 2012 10:49:25 +1000
From:	Anton Blanchard <anton@...ba.org>
To:	akinobu.mita@...il.com, akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] fault-inject: Avoid call to random32() if fault injection
 is disabled


After enabling CONFIG_FAILSLAB I noticed random32 in profiles even
if slub fault injection wasn't enabled at runtime.

should_fail forces a comparison against random32() even if
probability is 0:

        if (attr->probability <= random32() % 100)
                return false;

Add a check up front for probability == 0 and avoid all of the more
complicated checks.

Signed-off-by: Anton Blanchard <anton@...ba.org>
---

Index: linux-build/lib/fault-inject.c
===================================================================
--- linux-build.orig/lib/fault-inject.c	2012-02-11 21:22:32.303459860 +1100
+++ linux-build/lib/fault-inject.c	2012-02-11 22:38:10.470977505 +1100
@@ -101,6 +101,10 @@ static inline bool fail_stacktrace(struc
 
 bool should_fail(struct fault_attr *attr, ssize_t size)
 {
+	/* No need to check any other properties if the probability is 0 */
+	if (attr->probability == 0)
+		return false;
+
 	if (attr->task_filter && !fail_task(attr, current))
 		return false;
 
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