[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);

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)

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)
 {
 }

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

include/asm-i386/kexec.h

@@ -26,8 +26,5 @@
 #define KEXEC_ARCH KEXEC_ARCH_386
 
 #define MAX_NOTE_BYTES 1024
-typedef u32 note_buf_t[MAX_NOTE_BYTES/4];
-
-extern note_buf_t crash_notes[];
 
 #endif /* _I386_KEXEC_H */

include/asm-powerpc/kexec.h

@@ -38,9 +38,6 @@
 #ifdef CONFIG_KEXEC
 
 #define MAX_NOTE_BYTES 1024
-typedef u32 note_buf_t[MAX_NOTE_BYTES / sizeof(u32)];
-
-extern note_buf_t crash_notes[];
 
 #ifdef __powerpc64__
 extern void kexec_smp_wait(void);	/* get and clear naca physid, wait for

include/asm-s390/kexec.h

@@ -35,8 +35,5 @@
 #define KEXEC_ARCH KEXEC_ARCH_S390
 
 #define MAX_NOTE_BYTES 1024
-typedef u32 note_buf_t[MAX_NOTE_BYTES/4];
-
-extern note_buf_t crash_notes[];
 
 #endif /*_S390_KEXEC_H */

include/asm-x86_64/kexec.h

@@ -26,8 +26,5 @@
 #define KEXEC_ARCH KEXEC_ARCH_X86_64
 
 #define MAX_NOTE_BYTES 1024
-typedef u32 note_buf_t[MAX_NOTE_BYTES/4];
-
-extern note_buf_t crash_notes[];
 
 #endif /* _X86_64_KEXEC_H */

include/linux/kexec.h

@@ -125,6 +125,8 @@ extern struct kimage *kexec_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];
+extern note_buf_t *crash_notes;
 
 #else /* !CONFIG_KEXEC */
 struct pt_regs;

kernel/kexec.c

@@ -26,6 +26,9 @@
 #include <asm/system.h>
 #include <asm/semaphore.h>
 
+/* Per cpu memory for storing cpu states in case of system crash. */
+note_buf_t* crash_notes;
+
 /* Location of the reserved area for the crash kernel */
 struct resource crashk_res = {
 	.name  = "Crash kernel",
@@ -1060,3 +1063,16 @@ void crash_kexec(struct pt_regs *regs)
 		xchg(&kexec_lock, 0);
 	}
 }
+
+static int __init crash_notes_memory_init(void)
+{
+	/* Allocate memory for saving cpu registers. */
+	crash_notes = alloc_percpu(note_buf_t);
+	if (!crash_notes) {
+		printk("Kexec: Memory allocation for saving cpu register"
+		" states failed\n");
+		return -ENOMEM;
+	}
+	return 0;
+}
+module_init(crash_notes_memory_init)