kdump/kexec: calculate note size at compile time

Currently the size of the per-cpu region reserved to save crash notes is
set by the per-architecture value MAX_NOTE_BYTES.  Which in turn is
currently set to 1024 on all supported architectures.

While testing ia64 I recently discovered that this value is in fact too
small.  The particular setup I was using actually needs 1172 bytes.  This
lead to very tedious failure mode where the tail of one elf note would
overwrite the head of another if they ended up being alocated sequentially
by kmalloc, which was often the case.

It seems to me that a far better approach is to caclculate the size that
the area needs to be.  This patch does just that.

If a simpler stop-gap patch for ia64 to be squeezed into 2.6.21(.X) is
needed then this should be as easy as making MAX_NOTE_BYTES larger in
arch/asm-ia64/kexec.h.  Perhaps 2048 would be a good choice.  However, I
think that the approach in this patch is a much more robust idea.

Acked-by:  Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

11 files changed, 19 insertions, 20 deletions

diff --git a/arch/ia64/kernel/crash.c b/arch/ia64/kernel/crash.c
index 3d51a3f77017..aeb79fb28f0b 100644
--- a/arch/ia64/kernel/crash.c
+++ b/arch/ia64/kernel/crash.c
@@ -74,7 +74,7 @@ crash_save_this_cpu(void)
         buf = (u64 *) per_cpu_ptr(crash_notes, cpu);
         if (!buf)
                 return;
-        buf = append_elf_note(buf, "CORE", NT_PRSTATUS, prstatus,
+        buf = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS, prstatus,
                         sizeof(*prstatus));
         final_note(buf);
 }
diff --git a/include/asm-arm/kexec.h b/include/asm-arm/kexec.h
index 8c1c6162a80c..b5b030ef633d 100644
--- a/include/asm-arm/kexec.h
+++ b/include/asm-arm/kexec.h
@@ -16,8 +16,6 @@
 
 #ifndef __ASSEMBLY__
 
-#define MAX_NOTE_BYTES 1024
-
 struct kimage;
 /* Provide a dummy definition to avoid build failures. */
 static inline void crash_setup_regs(struct pt_regs *newregs,
diff --git a/include/asm-i386/kexec.h b/include/asm-i386/kexec.h
index bcb5b21de2d2..4b9dc9e6b701 100644
--- a/include/asm-i386/kexec.h
+++ b/include/asm-i386/kexec.h
@@ -45,8 +45,6 @@
 /* We can also handle crash dumps from 64 bit kernel. */
 #define vmcore_elf_check_arch_cross(x) ((x)->e_machine == EM_X86_64)
 
-#define MAX_NOTE_BYTES 1024
-
 /* CPU does not save ss and esp on stack if execution is already
  * running in kernel mode at the time of NMI occurrence. This code
  * fixes it.
diff --git a/include/asm-ia64/kexec.h b/include/asm-ia64/kexec.h
index 41299ddfee30..541be835fc5a 100644
--- a/include/asm-ia64/kexec.h
+++ b/include/asm-ia64/kexec.h
@@ -14,8 +14,6 @@
 /* The native architecture */
 #define KEXEC_ARCH KEXEC_ARCH_IA_64
 
-#define MAX_NOTE_BYTES 1024
-
 #define kexec_flush_icache_page(page) do { \
                 unsigned long page_addr = (unsigned long)page_address(page); \
                 flush_icache_range(page_addr, page_addr + PAGE_SIZE); \
diff --git a/include/asm-mips/kexec.h b/include/asm-mips/kexec.h
index b25267ebcb09..cdbab43b7d3a 100644
--- a/include/asm-mips/kexec.h
+++ b/include/asm-mips/kexec.h
@@ -21,8 +21,6 @@
 /* The native architecture */
 #define KEXEC_ARCH KEXEC_ARCH_MIPS
 
-#define MAX_NOTE_BYTES 1024
-
 static inline void crash_setup_regs(struct pt_regs *newregs,
                                     struct pt_regs *oldregs)
 {
diff --git a/include/asm-powerpc/kexec.h b/include/asm-powerpc/kexec.h
index 11cbdf81fd2e..b6f817b8ba3d 100644
--- a/include/asm-powerpc/kexec.h
+++ b/include/asm-powerpc/kexec.h
@@ -108,8 +108,6 @@ static inline void crash_setup_regs(struct pt_regs *newregs,
                                         struct pt_regs *oldregs) { }
 #endif /* !__powerpc64 __ */
 
-#define MAX_NOTE_BYTES 1024
-
 extern void kexec_smp_wait(void);       /* get and clear naca physid, wait for
                                           master to copy new code to 0 */
 extern int crashing_cpu;
diff --git a/include/asm-s390/kexec.h b/include/asm-s390/kexec.h
index 9c35c8ad1afd..7592af708b41 100644
--- a/include/asm-s390/kexec.h
+++ b/include/asm-s390/kexec.h
@@ -34,8 +34,6 @@
 /* The native architecture */
 #define KEXEC_ARCH KEXEC_ARCH_S390
 
-#define MAX_NOTE_BYTES 1024
-
 /* Provide a dummy definition to avoid build failures. */
 static inline void crash_setup_regs(struct pt_regs *newregs,
                                         struct pt_regs *oldregs) { }
diff --git a/include/asm-sh/kexec.h b/include/asm-sh/kexec.h
index da36a7548601..00f4260ef09b 100644
--- a/include/asm-sh/kexec.h
+++ b/include/asm-sh/kexec.h
@@ -26,8 +26,6 @@
 /* The native architecture */
 #define KEXEC_ARCH KEXEC_ARCH_SH
 
-#define MAX_NOTE_BYTES 1024
-
 static inline void crash_setup_regs(struct pt_regs *newregs,
                                     struct pt_regs *oldregs)
 {
diff --git a/include/asm-x86_64/kexec.h b/include/asm-x86_64/kexec.h
index 5fab957e1091..738e581b67f8 100644
--- a/include/asm-x86_64/kexec.h
+++ b/include/asm-x86_64/kexec.h
@@ -48,8 +48,6 @@
 /* The native architecture */
 #define KEXEC_ARCH KEXEC_ARCH_X86_64
 
-#define MAX_NOTE_BYTES 1024
-
 /*
  * Saving the registers of the cpu on which panic occured in
  * crash_kexec to save a valid sp. The registers of other cpus
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 696e5ec63f77..8c2c7fcd58ce 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -7,6 +7,8 @@
 #include <linux/linkage.h>
 #include <linux/compat.h>
 #include <linux/ioport.h>
+#include <linux/elfcore.h>
+#include <linux/elf.h>
 #include <asm/kexec.h>
 
 /* Verify architecture specific macros are defined */
@@ -31,6 +33,19 @@
 #error KEXEC_ARCH not defined
 #endif
 
+#define KEXEC_NOTE_HEAD_BYTES ALIGN(sizeof(struct elf_note), 4)
+#define KEXEC_CORE_NOTE_NAME "CORE"
+#define KEXEC_CORE_NOTE_NAME_BYTES ALIGN(sizeof(KEXEC_CORE_NOTE_NAME), 4)
+#define KEXEC_CORE_NOTE_DESC_BYTES ALIGN(sizeof(struct elf_prstatus), 4)
+/*
+ * The per-cpu notes area is a list of notes terminated by a "NULL"
+ * note header.  For kdump, the code in vmcore.c runs in the context
+ * of the second kernel to combine them into one note.
+ */
+#define KEXEC_NOTE_BYTES ( (KEXEC_NOTE_HEAD_BYTES * 2) +                \
+                            KEXEC_CORE_NOTE_NAME_BYTES +                \
+                            KEXEC_CORE_NOTE_DESC_BYTES )
+
 /*
  * This structure is used to hold the arguments that are used when loading
  * kernel binaries.
@@ -136,7 +151,7 @@ extern struct kimage *kexec_crash_image;
 /* Location of a reserved region to hold the crash kernel.
  */
 extern struct resource crashk_res;
-typedef u32 note_buf_t[MAX_NOTE_BYTES/4];
+typedef u32 note_buf_t[KEXEC_NOTE_BYTES/4];
 extern note_buf_t *crash_notes;
 
 
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 2a59c8a01ae0..25db14b89e82 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1118,8 +1118,8 @@ void crash_save_cpu(struct pt_regs *regs, int cpu)
         memset(&prstatus, 0, sizeof(prstatus));
         prstatus.pr_pid = current->pid;
         elf_core_copy_regs(&prstatus.pr_reg, regs);
-        buf = append_elf_note(buf, "CORE", NT_PRSTATUS, &prstatus,
-                                sizeof(prstatus));
+        buf = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS,
+                              &prstatus, sizeof(prstatus));
         final_note(buf);
 }