[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>

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);