[BUG FIX] [ARM/ARM26] find_memend_and_nodes bug fix

[Coywolf Qi Hunt]

Russell King wrote:

> On Tue, Jun 29, 2004 at 06:48:14PM +0800, Coywolf Qi Hunt wrote:
>  
>
> > Russell King wrote:
> > Actually there's physical DRAM offset: PHY_OFFSET, defined on ARM only. 
> > max_low_pfn happens to be the same as `num_lowpages'.
> > These assignments seems illogical in naming. But just happen to let this 
> > patch work.  Other platforms may still break.
> >    
>
> That may be a bug actually.  Looking at ll_rw_blk.c:
>
>        unsigned long bounce_pfn = dma_addr >> PAGE_SHIFT;
>        if (bounce_pfn < blk_max_low_pfn) {
>
>        blk_max_low_pfn = max_low_pfn;
>
> dma_addr are physical addresses, so bounce_pfn is referenced to a PFN0
> equal to physical address 0.  This implies that blk_max_low_pfn is
> likewise, as is max_low_pfn.
>
>  
>
> > [coywolf@everest ~/linux-2.6.7/arch]$ grep max_low_pfn arm* -rn
> > arm/mm/init.c:235:      max_low_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
> >    
>
> However, here, max_low_pfn of zero corresponds with the PFN of
> PHYS_OFFSET.  We have something with two different origins being
> compared, which is nonsense.  So something is wrong somewhere,
> and my money is on max_low_pfn.
>
>  
The bug may get into panic when there's still enough memory for block i/o.
Here's the patch with also a BUG_ON improvement.


=======================================================================

diff -Nrup linux-2.6.7/arch/arm/mm/init.c linux-2.6.7-cy2/arch/arm/mm/init.c
--- linux-2.6.7/arch/arm/mm/init.c	2004-06-29 23:03:30.000000000 -0500
+++ linux-2.6.7-cy2/arch/arm/mm/init.c	2004-06-30 04:32:42.215999091 -0500
@@ -231,9 +231,10 @@ find_memend_and_nodes(struct meminfo *mi
	 * This doesn't seem to be used by the Linux memory
	 * manager any more.  If we can get rid of it, we
	 * also get rid of some of the stuff above as well.
+	 *
+	 * blk_max_low_pfn depends on this. -- coywolf
	 */
-	max_low_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
-	max_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
+	max_low_pfn = max_pfn = memend_pfn;

	return bootmem_pages;
}
diff -Nrup linux-2.6.7/arch/arm26/mm/init.c linux-2.6.7-cy2/arch/arm26/mm/init.c
--- linux-2.6.7/arch/arm26/mm/init.c	2004-05-09 21:33:20.000000000 -0500
+++ linux-2.6.7-cy2/arch/arm26/mm/init.c	2004-06-30 03:59:51.000000000 -0500
@@ -160,9 +160,7 @@ find_memend_and_nodes(struct meminfo *mi

	np->bootmap_pages = 0;

-	if (mi->bank->size == 0) {
-		BUG();
-	}
+	BUG_ON(mi->bank->size == 0)

	/*
	 * Get the start and end pfns for this bank
@@ -183,9 +181,10 @@ find_memend_and_nodes(struct meminfo *mi
	 * This doesn't seem to be used by the Linux memory
	 * manager any more.  If we can get rid of it, we
	 * also get rid of some of the stuff above as well.
+	 *
+	 * blk_max_low_pfn depends on this. -- coywolf
	 */
-	max_low_pfn = memend_pfn - PFN_DOWN(PHYS_OFFSET);
-	max_pfn = memend_pfn - PFN_DOWN(PHYS_OFFSET);
+	max_low_pfn = max_pfn = memend_pfn;
	mi->end = memend_pfn << PAGE_SHIFT;

}

--

Coywolf Qi Hunt
Admin of http://GreatCN.org and http://LoveCN.org

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