[Crash-utility] [PATCH] s390: Fix backtrace code

[Michael Holzheu]

Hi Dave,

On Fri, 2010-02-26 at 09:50 -0500, Dave Anderson wrote:
> ----- "Michael Holzheu" <holzheu at linux.vnet.ibm.com> wrote:
> 
> > Hi Dave,
> > 
> > This patch fixes several bugs in the s390 stack backtrace code
> > * Add panic stack as second interrupt stack
> > * Fix printing of access registers (4 bytes instead of 8 bytes)
> > * Use u64 for s390x register 14
> > * Fix interrupt stack handling for s390x (use 160 byte overhead
> > instead of 96)
> 
> The patch looks OK upon first glance -- can you verify that it's
> absolutely backwards-compatible to earlier kernel versions?

I tested vanilla 2.6.32, RHEL5, SLES10 and SLES11.

But I found a bug with RHEL4:

Older Linux kernels for s390 can be built so that the panic stack is
not set (CONFIG_CHECK_STACK kernel built option):

 *(lowcore_ptr[i]) = S390_lowcore;
 lowcore_ptr[i]->async_stack = stack + (ASYNC_SIZE);

#ifdef CONFIG_CHECK_STACK
     stack = __get_free_pages(GFP_KERNEL,0);
     if (stack == 0ULL)
            panic("smp_boot_cpus failed to allocate memory\n");
     lowcore_ptr[i]->panic_stack = stack + (PAGE_SIZE);
#endif

RHEL4 has not defined CONFIG_CHECK_STACK. Therefore the following
patch adds a check, so that the panic stack is only used, when
it is there.
---
 s390.c  |    2 ++
 s390x.c |    2 ++
 2 files changed, 4 insertions(+)

--- a/s390.c
+++ b/s390.c
@@ -581,6 +581,8 @@ static void s390_get_int_stack(char *sta
 	if (!MEMBER_EXISTS("_lowcore", stack_name))
 		return;
 	stack_addr = ULONG(lc + MEMBER_OFFSET("_lowcore", stack_name));
+	if (stack_addr == 0)
+		return;
 	readmem(stack_addr - INT_STACK_SIZE, KVADDR, int_stack,
 		INT_STACK_SIZE, stack_name, FAULT_ON_ERROR);
 	*start = stack_addr - INT_STACK_SIZE;
--- a/s390x.c
+++ b/s390x.c
@@ -813,6 +813,8 @@ static void s390x_get_int_stack(char *st
 	if (!MEMBER_EXISTS("_lowcore", stack_name))
 		return;
 	stack_addr = ULONG(lc + MEMBER_OFFSET("_lowcore", stack_name));
+	if (stack_addr == 0)
+		return;
 	readmem(stack_addr - INT_STACK_SIZE, KVADDR, int_stack,
 		INT_STACK_SIZE, stack_name, FAULT_ON_ERROR);
 	*start = stack_addr - INT_STACK_SIZE;

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