Re: kexec/kdump: Use generic elf code on ia64

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Hi Nanhai,

could you take a moment to look at this patch to see if it
addresses your concern about stack usage?

-- 
Horms
  H: http://www.vergenet.net/~horms/
  W: http://www.valinux.co.jp/en/

On Wed, Apr 25, 2007 at 06:09:05PM +0900, Simon Horman wrote:
> Make use of the generic implementation of crash_save_cpu().
> 
> On ia64 the registers are saved by a kdump-specific function
> ia64_dump_cpu_regs() rather than elf_core_copy_regs() which
> is used by other architectures via crash_save_cpu(). It seems
> that ia64_dump_cpu_regs() and elf_core_copy_regs() are indeed
> quite different
> 
> In order to facilitate this kdump_elf_core_copy_regs()
> has been created, and it is called by crash_save_cpu().
> By default kdump_elf_core_copy_regs() is just defined to be
> elf_core_copy_regs() and ia64 defines its own implementation,
> which calls ia64_dump_cpu_regs().  The ia64 version also sets
> register 47 in accordance with the code that it replaces.
> 
> crash_save_cpu() has also been modifued to use a pre-alocated,
> per-cpu variable for saving the cpu registers, as per the
> IA64 specific code that this patch removes. This is
> in order to reduce possible stack contention at crash-time.
> 
> The code appears to work, however as the place where the registers
> are captured has changed natrually some of their values have also changed.
> This makes looking for problems by comparing the new and old output a
> little tricky.
> 
> Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>
> 
> --- 
> * This patch applies on top of the note size calculation patch
>   that can be found in mm and at
>   http://lists.linux-foundation.org/pipermail/fastboot/2007-April/006792.html
> 
>   Porting this patch to not require that one is quite trivial.
>   I can supply a port or a thread containing both patches if it helps.
> 
> * Update
>   Diff against include/asm-ia64/kexec.h instead of include/asm/kexec.h
>   Ooops!
> 
> * Updated crash_save_cpu() to use a per-cpu variable for the registers.
>   As requested by Nanhai Zou
> 
> * This patch does three things, should it be split?
>   - Makes crash_save_cpu() use a per-cpu variable.
>   - Adds the kdump_elf_core_copy_regs() macro
>   - Has IA64 use the generic code (which requires the other two changes).
> 
> * Added CC: kexec@xxxxxxxxxxxxxxxxxxx, which is the new place for kexec
>   discussion.
> 
>  arch/ia64/kernel/crash.c         |   46 ++------------------------------------
>  arch/ia64/kernel/machine_kexec.c |    2 -
>  include/asm-ia64/kexec.h         |    7 ++++-
>  include/linux/kexec.h            |    5 ++++
>  kernel/kexec.c                   |   13 +++++++++-
>  5 files changed, 26 insertions(+), 47 deletions(-)
> Index: linux-2.6/arch/ia64/kernel/crash.c
> ===================================================================
> --- linux-2.6.orig/arch/ia64/kernel/crash.c	2007-04-25 17:31:54.000000000 +0900
> +++ linux-2.6/arch/ia64/kernel/crash.c	2007-04-25 17:31:55.000000000 +0900
> @@ -25,44 +25,11 @@ static atomic_t kdump_cpu_frozen;
>  atomic_t kdump_in_progress;
>  static int kdump_on_init = 1;
>  
> -static inline Elf64_Word
> -*append_elf_note(Elf64_Word *buf, char *name, unsigned type, void *data,
> -		size_t data_len)
> -{
> -	struct elf_note *note = (struct elf_note *)buf;
> -	note->n_namesz = strlen(name) + 1;
> -	note->n_descsz = data_len;
> -	note->n_type   = type;
> -	buf += (sizeof(*note) + 3)/4;
> -	memcpy(buf, name, note->n_namesz);
> -	buf += (note->n_namesz + 3)/4;
> -	memcpy(buf, data, data_len);
> -	buf += (data_len + 3)/4;
> -	return buf;
> -}
> -
> -static void
> -final_note(void *buf)
> -{
> -	memset(buf, 0, sizeof(struct elf_note));
> -}
> -
> -extern void ia64_dump_cpu_regs(void *);
> -
> -static DEFINE_PER_CPU(struct elf_prstatus, elf_prstatus);
> -
>  void
> -crash_save_this_cpu(void)
> +ia64_kexec_elf_core_copy_regs(elf_gregset_t *elfregs, struct pt_regs *regs)
>  {
> -	void *buf;
>  	unsigned long cfm, sof, sol;
> -
> -	int cpu = smp_processor_id();
> -	struct elf_prstatus *prstatus = &per_cpu(elf_prstatus, cpu);
> -
> -	elf_greg_t *dst = (elf_greg_t *)&(prstatus->pr_reg);
> -	memset(prstatus, 0, sizeof(*prstatus));
> -	prstatus->pr_pid = current->pid;
> +	elf_greg_t *dst = (elf_greg_t *)elfregs;
>  
>  	ia64_dump_cpu_regs(dst);
>  	cfm = dst[43];
> @@ -70,13 +37,6 @@ crash_save_this_cpu(void)
>  	sof = cfm & 0x7f;
>  	dst[46] = (unsigned long)ia64_rse_skip_regs((unsigned long *)dst[46],
>  			sof - sol);
> -
> -	buf = (u64 *) per_cpu_ptr(crash_notes, cpu);
> -	if (!buf)
> -		return;
> -	buf = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS, prstatus,
> -			sizeof(*prstatus));
> -	final_note(buf);
>  }
>  
>  #ifdef CONFIG_SMP
> @@ -134,7 +94,7 @@ kdump_cpu_freeze(struct unw_frame_info *
>  	int cpuid;
>  	local_irq_disable();
>  	cpuid = smp_processor_id();
> -	crash_save_this_cpu();
> +	crash_save_cpu(NULL, smp_processor_id());
>  	current->thread.ksp = (__u64)info->sw - 16;
>  	atomic_inc(&kdump_cpu_frozen);
>  	kdump_status[cpuid] = 1;
> Index: linux-2.6/include/asm-ia64/kexec.h
> ===================================================================
> --- linux-2.6.orig/include/asm-ia64/kexec.h	2007-04-25 17:31:54.000000000 +0900
> +++ linux-2.6/include/asm-ia64/kexec.h	2007-04-25 17:31:55.000000000 +0900
> @@ -19,6 +19,9 @@
>                  flush_icache_range(page_addr, page_addr + PAGE_SIZE); \
>          } while(0)
>  
> +#define kexec_elf_core_copy_regs(elfregs, regs) \
> +	ia64_kexec_elf_core_copy_regs(elfregs, regs)
> +
>  extern struct kimage *ia64_kimage;
>  extern const unsigned int relocate_new_kernel_size;
>  extern void relocate_new_kernel(unsigned long, unsigned long,
> @@ -32,7 +35,9 @@ extern struct resource boot_param_res;
>  extern void kdump_smp_send_stop(void);
>  extern void kdump_smp_send_init(void);
>  extern void kexec_disable_iosapic(void);
> -extern void crash_save_this_cpu(void);
> +extern void ia64_dump_cpu_regs(void *);
> +extern void ia64_kexec_elf_core_copy_regs(elf_gregset_t *elfregs,
> +					  struct pt_regs *regs);
>  struct rsvd_region;
>  extern unsigned long kdump_find_rsvd_region(unsigned long size,
>  		struct rsvd_region *rsvd_regions, int n);
> Index: linux-2.6/include/linux/kexec.h
> ===================================================================
> --- linux-2.6.orig/include/linux/kexec.h	2007-04-25 17:31:54.000000000 +0900
> +++ linux-2.6/include/linux/kexec.h	2007-04-25 17:31:55.000000000 +0900
> @@ -128,6 +128,11 @@ extern struct kimage *kexec_crash_image;
>  #define kexec_flush_icache_page(page)
>  #endif
>  
> +#ifndef kexec_elf_core_copy_regs
> +#define kexec_elf_core_copy_regs(elfregs, regs) \
> +	elf_core_copy_regs(elfregs, regs)
> +#endif
> +
>  #define KEXEC_ON_CRASH  0x00000001
>  #define KEXEC_ARCH_MASK 0xffff0000
>  
> Index: linux-2.6/kernel/kexec.c
> ===================================================================
> --- linux-2.6.orig/kernel/kexec.c	2007-04-25 17:31:54.000000000 +0900
> +++ linux-2.6/kernel/kexec.c	2007-04-25 17:57:12.000000000 +0900
> @@ -1097,9 +1097,18 @@ static void final_note(u32 *buf)
>  	memcpy(buf, &note, sizeof(note));
>  }
>  
> +/*
> + * There is some concern that on architectures where struct elf_prstatus is
> + * large, such as IA64, having elf_prstatus on the stack in
> + * crash_save_cpu() could cause problems given that this function
> + * is run after a kernel crash has occured. To aleviate this problem
> + * a pre-allocated per-cpu value is used instead.
> + */
> +static DEFINE_PER_CPU(struct elf_prstatus, elf_prstatus);
> +
>  void crash_save_cpu(struct pt_regs *regs, int cpu)
>  {
> -	struct elf_prstatus prstatus;
> +	struct elf_prstatus *prstatus;
>  	u32 *buf;
>  
>  	if ((cpu < 0) || (cpu >= NR_CPUS))
> @@ -1107,7 +1116,7 @@ void crash_save_cpu(struct pt_regs *regs
>  
>  	/* Using ELF notes here is opportunistic.
>  	 * I need a well defined structure format
> -	 * for the data I pass, and I need tags
> +	 * for the data I pass, and I need tag)s
>  	 * on the data to indicate what information I have
>  	 * squirrelled away.  ELF notes happen to provide
>  	 * all of that, so there is no need to invent something new.
> @@ -1115,11 +1124,12 @@ void crash_save_cpu(struct pt_regs *regs
>  	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);
> +	prstatus = &per_cpu(elf_prstatus, cpu);
> +	memset(prstatus, 0, sizeof(struct elf_prstatus));
> +	prstatus->pr_pid = current->pid;
> +	kexec_elf_core_copy_regs(&(prstatus->pr_reg), regs);
>  	buf = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS,
> -		      	      &prstatus, sizeof(prstatus));
> +			      prstatus, sizeof(struct elf_prstatus));
>  	final_note(buf);
>  }
>  
> Index: linux-2.6/arch/ia64/kernel/machine_kexec.c
> ===================================================================
> --- linux-2.6.orig/arch/ia64/kernel/machine_kexec.c	2007-04-25 17:31:54.000000000 +0900
> +++ linux-2.6/arch/ia64/kernel/machine_kexec.c	2007-04-25 17:31:55.000000000 +0900
> @@ -84,7 +84,7 @@ static void ia64_machine_kexec(struct un
>  
>  	BUG_ON(!image);
>  	if (image->type == KEXEC_TYPE_CRASH) {
> -		crash_save_this_cpu();
> +		crash_save_cpu(NULL, smp_processor_id());
>  		current->thread.ksp = (__u64)info->sw - 16;
>  	}
>  
> -
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