[PATCH] kdump: dynamic per cpu allocation of memory for saving cpu registers

- In case of system crash, current state of cpu registers is saved in memory
  in elf note format.  So far memory for storing elf notes was being allocated
  statically for NR_CPUS.

- This patch introduces dynamic allocation of memory for storing elf notes.
  It uses alloc_percpu() interface.  This should lead to better memory usage.

- Introduced based on Andi Kleen's and Eric W. Biederman's suggestions.

- This patch also moves memory allocation for elf notes from architecture
  dependent portion to architecture independent portion.  Now crash_notes is
  architecture independent.  The whole idea is that size of memory to be
  allocated per cpu (MAX_NOTE_BYTES) can be architecture dependent and
  allocation of this memory can be architecture independent.

Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

4 files changed, 3 insertions, 12 deletions

diff --git a/arch/i386/kernel/crash.c b/arch/i386/kernel/crash.c
index 10fe6569751e77..f1e65c2ead6e09 100644
--- a/arch/i386/kernel/crash.c
+++ b/arch/i386/kernel/crash.c
@@ -25,7 +25,6 @@
 #include <mach_ipi.h>
 
 
-note_buf_t crash_notes[NR_CPUS];
 /* This keeps a track of which one is crashing cpu. */
 static int crashing_cpu;
 
@@ -72,7 +71,9 @@ static void crash_save_this_cpu(struct pt_regs *regs, int cpu)
 	 * squirrelled away.  ELF notes happen to provide
 	 * all of that that no need to invent something new.
 	 */
-	buf = &crash_notes[cpu][0];
+	buf = (u32*)per_cpu_ptr(crash_notes, cpu);
+	if (!buf)
+		return;
 	memset(&prstatus, 0, sizeof(prstatus));
 	prstatus.pr_pid = current->pid;
 	elf_core_copy_regs(&prstatus.pr_reg, regs);
diff --git a/arch/ppc/kernel/machine_kexec.c b/arch/ppc/kernel/machine_kexec.c
index a882b0dbe8de3e..84d65a87191ed6 100644
--- a/arch/ppc/kernel/machine_kexec.c
+++ b/arch/ppc/kernel/machine_kexec.c
@@ -28,12 +28,6 @@ typedef NORET_TYPE void (*relocate_new_kernel_t)(
 const extern unsigned char relocate_new_kernel[];
 const extern unsigned int relocate_new_kernel_size;
 
-/*
- * Provide a dummy crash_notes definition while crash dump arrives to ppc.
- * This prevents breakage of crash_notes attribute in kernel/ksysfs.c.
- */
-note_buf_t crash_notes[NR_CPUS];
-
 void machine_shutdown(void)
 {
 	if (ppc_md.machine_shutdown)
diff --git a/arch/s390/kernel/crash.c b/arch/s390/kernel/crash.c
index 7bd169c58b0c22..926cceeae0faa2 100644
--- a/arch/s390/kernel/crash.c
+++ b/arch/s390/kernel/crash.c
@@ -10,8 +10,6 @@
 #include <linux/threads.h>
 #include <linux/kexec.h>
 
-note_buf_t crash_notes[NR_CPUS];
-
 void machine_crash_shutdown(struct pt_regs *regs)
 {
 }
diff --git a/arch/x86_64/kernel/crash.c b/arch/x86_64/kernel/crash.c
index 535e0446607985..efe450760bbcbc 100644
--- a/arch/x86_64/kernel/crash.c
+++ b/arch/x86_64/kernel/crash.c
@@ -19,8 +19,6 @@
 #include <asm/nmi.h>
 #include <asm/hw_irq.h>
 
-note_buf_t crash_notes[NR_CPUS];
-
 void machine_crash_shutdown(struct pt_regs *regs)
 {
 	/* This function is only called after the system