[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>

10 files changed, 21 insertions, 24 deletions

diff --git a/arch/i386/kernel/crash.c b/arch/i386/kernel/crash.c
index 10fe6569751e..f1e65c2ead6e 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 a882b0dbe8de..84d65a87191e 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 7bd169c58b0c..926cceeae0fa 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 535e04466079..efe450760bbc 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
diff --git a/include/asm-i386/kexec.h b/include/asm-i386/kexec.h
index 6ed2a03e37b3..d80d446498fb 100644
--- a/include/asm-i386/kexec.h
+++ b/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 */
diff --git a/include/asm-powerpc/kexec.h b/include/asm-powerpc/kexec.h
index 4263af3cadfd..e363752276ef 100644
--- a/include/asm-powerpc/kexec.h
+++ b/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
diff --git a/include/asm-s390/kexec.h b/include/asm-s390/kexec.h
index 54cf7d9f251c..b4809d98fe69 100644
--- a/include/asm-s390/kexec.h
+++ b/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 */
diff --git a/include/asm-x86_64/kexec.h b/include/asm-x86_64/kexec.h
index 42d2ff15c592..cea78543a574 100644
--- a/include/asm-x86_64/kexec.h
+++ b/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 */
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index c8468472aec0..c1cd9b31159e 100644
--- a/include/linux/kexec.h
+++ b/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;
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 2c95848fbce8..1197de8b2a94 100644
--- a/kernel/kexec.c
+++ b/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)