linux-kernel - [PATCH v2] kdump: crashk_res init check for /sys/kernel/kexec_crash

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Date:	Wed, 23 Nov 2011 14:18:03 +0100
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	akpm@...ux-foundation.org
Cc:	Simon Horman <horms@...ge.net.au>, heiko.carstens@...ibm.com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	schwidefsky@...ibm.com, akpm@...ux-foundation.org,
	Vivek Goyal <vgoyal@...hat.com>
Subject: [PATCH v2] kdump: crashk_res init check for
 /sys/kernel/kexec_crash_size

From: Michael Holzheu <holzheu@...ux.vnet.ibm.com>

Currently it is possible to set the crash_size via the sysfs
/sys/kernel/kexec_crash_size even if no crash kernel memory has
been defined with the "crashkernel" parameter. In this case
"crashk_res" is not initialized and crashk_res.start = crashk_res.end = 0.
Unfortunately resource_size(&crashk_res) returns 1 in this case.
This breaks the s390 implementation of crash_(un)map_reserved_pages().

To fix the problem the correct "old_size" is now calculated in
crash_shrink_memory(). "old_size is set to "0" if crashk_res is
not initialized. With this change crash_shrink_memory() will do nothing,
when "crashk_res" is not initialized. It will return "0" for
"echo 0 > /sys/kernel/kexec_crash_size" and -EINVAL for
"echo [not zero] > /sys/kernel/kexec_crash_size".

In addition to that this patch also simplifies the "ret = -EINVAL"
vs. "ret = 0" logic as suggested by Simon Horman.

Cc: Simon Horman <horms@...ge.net.au>
Signed-off-by: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
---
 kernel/kexec.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1131,7 +1131,7 @@ void __weak crash_free_reserved_phys_ran
 int crash_shrink_memory(unsigned long new_size)
 {
 	int ret = 0;
-	unsigned long start, end;
+	unsigned long start, end, old_size;

 	mutex_lock(&kexec_mutex);

@@ -1141,11 +1141,9 @@ int crash_shrink_memory(unsigned long ne
 	}
 	start = crashk_res.start;
 	end = crashk_res.end;
-
-	if (new_size >= end - start + 1) {
-		ret = -EINVAL;
-		if (new_size == end - start + 1)
-			ret = 0;
+	old_size = (end == 0) ? 0 : end - start + 1;
+	if (new_size >= old_size) {
+		ret = (new_size == old_size) ? 0 : -EINVAL;
 		goto unlock;
 	}

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