kdump: crashk_res init check for /sys/kernel/kexec_crash_size

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.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Reviewed-by: Dave Young <dyoung@redhat.com>
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Reviewed-by: Simon Horman <horms@verge.net.au>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/kexec.c b/kernel/kexec.c
index c85392fbbf619a0a8807eb08cd42816f6fa87bfd..4a17bac99cf8f0b519b1c86d8f9a6643bed8aa63 100644 (file)
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1129,6 +1129,7 @@ int crash_shrink_memory(unsigned long new_size)
 {
        int ret = 0;
        unsigned long start, end;
+       unsigned long old_size;
        struct resource *ram_res;
 
        mutex_lock(&kexec_mutex);
@@ -1139,11 +1140,9 @@ int crash_shrink_memory(unsigned long new_size)
        }
        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;
        }