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 at verge.net.au> Cc: Vivek Goyal <vgoyal at redhat.com> Signed-off-by: Andrew Morton <akpm at 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) {
