The patch titled
kdump: add is_vmcore_usable() and vmcore_unusable()
has been added to the -mm tree. Its filename is
kdump-add-is_vmcore_usable-and-vmcore_unusable.patch
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------------------------------------------------------
Subject: kdump: add is_vmcore_usable() and vmcore_unusable()
From: Simon Horman <horms@xxxxxxxxxxxx>
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@xxxxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/vmcore.c | 2 +-
include/linux/crash_dump.h | 26 ++++++++++++++++++++++++++
2 files changed, 27 insertions(+), 1 deletion(-)
diff -puN fs/proc/vmcore.c~kdump-add-is_vmcore_usable-and-vmcore_unusable fs/proc/vmcore.c
--- a/fs/proc/vmcore.c~kdump-add-is_vmcore_usable-and-vmcore_unusable
+++ a/fs/proc/vmcore.c
@@ -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) {
diff -puN include/linux/crash_dump.h~kdump-add-is_vmcore_usable-and-vmcore_unusable include/linux/crash_dump.h
--- a/include/linux/crash_dump.h~kdump-add-is_vmcore_usable-and-vmcore_unusable
+++ a/include/linux/crash_dump.h
@@ -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;
@@ -42,5 +43,30 @@ static inline int is_kdump_kernel(void)
static inline int is_kdump_kernel(void) { return 0; }
#endif /* CONFIG_CRASH_DUMP */
+#ifdef CONFIG_PROC_VMCORE
+/* 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 1 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;
+}
+#endif /* CONFIG_PROC_VMCORE */
+
extern unsigned long saved_max_pfn;
#endif /* LINUX_CRASHDUMP_H */
_
Patches currently in -mm which might be from horms@xxxxxxxxxxxx are
origin.patch
linux-next.patch
kdump-make-elfcorehdr_addr-independent-of-config_proc_vmcore.patch
kdump-update-elfcorehdr-documentation-to-reflect-supported-architectures.patch
kdump-use-is_kdump_kernel-in-sba_init.patch
kdump-add-is_vmcore_usable-and-vmcore_unusable.patch
kdump-use-is_vmcore_usable-and-vmcore_unusable-in-reserve_elfcorehdr.patch
kdump-ia64-always-reserve-elfcore-header-memory-in-crash-kernel.patch
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