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SubjectRe: 2.5.55/.56 instant reboot problem on 486
Mikael Pettersson wrote:
> My '94 vintage 486 has problems booting 2.5.55 and 2.5.56.
> When it fails, the boot gets to loading the kernel and
> printing "Ok, booting the kernel.". Then there is a short
> pause (line a tenth of a second) and the machine reboots.
>
> After doing a binary search with "for(;;);" statements
> (printk doesn't work this early) I found that the reboot
> occurs in arch/i386/mm/init.c:kernel_physical_mapping_init():
> (start_kernel() -> setup_arch() -> paging_init() ->
> pagetable_init() -> kernel_physical_mapping_init())
>

The problem is that one_page_table_init() pulls the rug out from under
the kernel by installing a new page table before setting it up. A 486
has a small TLB so any miss will cause a triple fault and reset. Try
this patch and see if it fixes it.

--
Brian Gerst
diff -urN linux-2.5.56/arch/i386/mm/init.c linux/arch/i386/mm/init.c
--- linux-2.5.56/arch/i386/mm/init.c Sun Jan 12 00:16:22 2003
+++ linux/arch/i386/mm/init.c Sun Jan 12 01:48:28 2003
@@ -71,12 +71,16 @@
*/
static pte_t * __init one_page_table_init(pmd_t *pmd)
{
- pte_t *page_table = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
- set_pmd(pmd, __pmd(__pa(page_table) | _PAGE_TABLE));
- if (page_table != pte_offset_kernel(pmd, 0))
- BUG();
+ if (pmd_none(*pmd)) {
+ pte_t *page_table = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
+ set_pmd(pmd, __pmd(__pa(page_table) | _PAGE_TABLE));
+ if (page_table != pte_offset_kernel(pmd, 0))
+ BUG();

- return page_table;
+ return page_table;
+ }
+
+ return pte_offset_kernel(pmd, 0);
}

/*
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