lkml.org 
[lkml]   [2008]   [Aug]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [patch 5/6] kdump: add is_vmcore_usable() and vmcore_unusable()
The usage of elfcorehdr_addr has changed recently
such that being set to ELFCORE_ADDR_MAX is used by
is_kdump_kernel() to indicate if the code is executing
in a kernel executed as a crash kernel.

However, arch/ia64/kernel/setup.c:reserve_elfcorehdr will
rest elfcorehdr_addr to ELFCORE_ADDR_MAX on error,
which means any subsequent calls to is_kdump_kernel()
will return 0, even though they should return 1.

Ok, at this point in time there are no subsequent calls,
but I think its fair to say that there is ample scope for error
or at the very least confusion.

This patch add an extra state, ELFCORE_ADDR_ERR, which
indicates that elfcorehdr_addr was passed on the command line,
and thus execution is taking place in a crashdump kernel,
but vmcore can't be used for some reason. This is tested
for using is_vmcore_usable() and set using vmcore_unusable().
A subsequent patch makes use of this new code.

To summarise, the states that elfcorehdr_addr can now be in are as follows:

ELFCORE_ADDR_MAX: not a crashdump kernel
ELFCORE_ADDR_ERR: crashdump kernel but vmcore is unusable
any other value: crash dump kernel and vmcore is usable

Signed-off-by: Simon Horman <horms@verge.net.au>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

---

fs/proc/vmcore.c | 2 +-
include/linux/crash_dump.h | 26 ++++++++++++++++++++++++++
2 files changed, 27 insertions(+), 1 deletion(-)

Wed, 30 Jul 2008 09:10:37 +1000
* Fixed logic bug in vmcore_unusable().
if (!is_kdump_kernel()) is correct
if (is_kdump_kernel()) is not

Wed, 06 Aug 2008 09:53:44 +1000
* is_vmcore_usable() and vmcore_unusable may be used when
CONFIG_CRASH_DUMP is defined but CONFIG_PROC_VMCORE is not.

This update is needed by
"kdump, ia64: always reserve elfcore header memory in crash kernel"
http://lists.infradead.org/pipermail/kexec/2008-August/002294.html

Index: linux-2.6/include/linux/crash_dump.h
===================================================================
--- linux-2.6.orig/include/linux/crash_dump.h 2008-08-05 18:10:21.000000000 +1000
+++ linux-2.6/include/linux/crash_dump.h 2008-08-05 18:11:14.000000000 +1000
@@ -8,6 +8,7 @@
#include <linux/proc_fs.h>

#define ELFCORE_ADDR_MAX (-1ULL)
+#define ELFCORE_ADDR_ERR (-2ULL)

extern unsigned long long elfcorehdr_addr;

@@ -38,6 +39,29 @@ static inline int is_kdump_kernel(void)
{
return (elfcorehdr_addr != ELFCORE_ADDR_MAX) ? 1 : 0;
}
+
+/* is_vmcore_usable() checks if the kernel is booting after a panic and
+ * the vmcore region is usable.
+ *
+ * This makes use of the fact that due to alignment -2ULL is not
+ * a valid pointer, much in the vain of IS_ERR(), except
+ * dealing directly with an unsigned long long rather than a pointer.
+ */
+
+static inline int is_vmcore_usable(void)
+{
+ return is_kdump_kernel() && elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
+}
+
+/* vmcore_unusable() marks the vmcore as unusable,
+ * without disturbing the logic of is_kdump_kernel()
+ */
+
+static inline void vmcore_unusable(void)
+{
+ if (is_kdump_kernel())
+ elfcorehdr_addr = ELFCORE_ADDR_ERR;
+}
#else /* !CONFIG_CRASH_DUMP */
static inline int is_kdump_kernel(void) { return 0; }
#endif /* CONFIG_CRASH_DUMP */
Index: linux-2.6/fs/proc/vmcore.c
===================================================================
--- linux-2.6.orig/fs/proc/vmcore.c 2008-08-05 18:10:21.000000000 +1000
+++ linux-2.6/fs/proc/vmcore.c 2008-08-05 18:10:25.000000000 +1000
@@ -650,7 +650,7 @@ static int __init vmcore_init(void)
int rc = 0;

/* If elfcorehdr= has been passed in cmdline, then capture the dump.*/
- if (!(elfcorehdr_addr < ELFCORE_ADDR_MAX))
+ if (!(is_vmcore_usable()))
return rc;
rc = parse_crash_elf_headers();
if (rc) {


\
 
 \ /
  Last update: 2008-08-06 02:47    [W:0.077 / U:1.312 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site