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SubjectRe: [PATCH] alloc_bootmem_core: fix misaligned allocation of 1G page
On Wed, Aug 13, 2008 at 08:18:04PM +0200, Johannes Weiner wrote:
> Andreas Herrmann <andreas.herrmann3@amd.com> writes:

> > Otherwise the function can't allocate the first possible page. For
> > example, assuming that
> >
> > node_min_pfn = 130000
> > align = 0x40000000 (1GByte)
> >
> > allocating a 1G page on this node will result in
> >
> > sidx=0x40000
> > min_pfn=0x140000
> >
> > Both are properly aligned. But the resulting super-page will be at
> > address 0x180000000 whereas the first possible 1G page would be at
> > address 0x140000000.
>
> I can not follow this example. Is there a typo somewhere? In this
> example, the resulting address is aligned but it shouldn't even be so.

No typo. I guess the confusion is just my ambiguous wording.
It's what your previous patch generated. At the end it "aligned" the first
1G page on node 1 at 0x180000000 (== the return value of alloc_bootmem_core)
but it reserved the region from 0x170000000:
Aug 13 16:05:49 brandon bootmem::alloc_bootmem_core nid=1 size=40000000
[262144 pages] align=40000000 goal=0 limit=0
Aug 13 16:05:49 brandon bootmem::__reserve nid=1 start=170000 end=1b0000 flags=1
Aug 13 16:05:49 brandon addr:ffff880180000000, paddr:0000000180000000, size: 1073741824
... and after some time ...

BUG: unable to handle kernel NULL pointer dereference at 000000000000000a
IP: [<ffffffff80261a87>] get_page_from_freelist+0x403/0x5ed
PGD 22f108067 PUD 22dc3d067 PMD 0
Oops: 0000 [1] SMP
...

> Attached is a version that should be easier to read. Please
> double-check.

Nice.
That's the preferred solution and should replace my initial fix.

Reviewed-and-tested-by: Andreas Herrmann <andreas.herrmann3@amd.com>


Thanks,

Andreas


> commit ec5b91737d0be242a6a9b255fa1749962f978188
> Author: Johannes Weiner <hannes@saeurebad.de>
> Date: Wed Aug 13 19:59:43 2008 +0200
>
> bootmem: fix aligning of node-relative indexes and offsets
>
> diff --git a/mm/bootmem.c b/mm/bootmem.c
> index 4af15d0..8620832 100644
> --- a/mm/bootmem.c
> +++ b/mm/bootmem.c
> @@ -405,6 +405,30 @@ int __init reserve_bootmem(unsigned long addr, unsigned long size,
> }
> #endif /* !CONFIG_HAVE_ARCH_BOOTMEM_NODE */
>
> +static unsigned long align_idx(struct bootmem_data *bdata, unsigned long idx,
> + unsigned long step)
> +{
> + unsigned long base = bdata->node_min_pfn;
> +
> + /*
> + * Align the index with respect to the node start so that the
> + * resulting absolute PFN (node-start + index) is properly
> + * aligned.
> + */
> +
> + return ALIGN(base + idx, step) - base;
> +}
> +
> +static unsigned long align_off(struct bootmem_data *bdata, unsigned long off,
> + unsigned long align)
> +{
> + unsigned long base = PFN_PHYS(bdata->node_min_pfn);
> +
> + /* Same as align_idx for byte offsets */
> +
> + return ALIGN(base + off, align) - base;
> +}
> +
> static void * __init alloc_bootmem_core(struct bootmem_data *bdata,
> unsigned long size, unsigned long align,
> unsigned long goal, unsigned long limit)
> @@ -441,16 +465,23 @@ static void * __init alloc_bootmem_core(struct bootmem_data *bdata,
> else
> start = ALIGN(min, step);
>
> - sidx = start - bdata->node_min_pfn;;
> + sidx = start - bdata->node_min_pfn;
> midx = max - bdata->node_min_pfn;
>
> + /*
> + * Because the indexes are relative to the node, all alignment
> + * below has to be done with respect to the node's start in
> + * order to have the resulting PFNs and addresses properly
> + * aligned.
> + */
> +
> if (bdata->hint_idx > sidx) {
> /*
> * Handle the valid case of sidx being zero and still
> * catch the fallback below.
> */
> fallback = sidx + 1;
> - sidx = ALIGN(bdata->hint_idx, step);
> + sidx = align_idx(bdata, bdata->hint_idx, step);
> }
>
> while (1) {
> @@ -459,7 +490,7 @@ static void * __init alloc_bootmem_core(struct bootmem_data *bdata,
> unsigned long eidx, i, start_off, end_off;
> find_block:
> sidx = find_next_zero_bit(bdata->node_bootmem_map, midx, sidx);
> - sidx = ALIGN(sidx, step);
> + sidx = align_idx(bdata, sidx, step);
> eidx = sidx + PFN_UP(size);
>
> if (sidx >= midx || eidx > midx)
> @@ -467,7 +498,7 @@ find_block:
>
> for (i = sidx; i < eidx; i++)
> if (test_bit(i, bdata->node_bootmem_map)) {
> - sidx = ALIGN(i, step);
> + sidx = align_idx(bdata, i, step);
> if (sidx == i)
> sidx += step;
> goto find_block;
> @@ -475,7 +506,7 @@ find_block:
>
> if (bdata->last_end_off &&
> PFN_DOWN(bdata->last_end_off) + 1 == sidx)
> - start_off = ALIGN(bdata->last_end_off, align);
> + start_off = align_off(bdata, bdata->last_end_off, align);
> else
> start_off = PFN_PHYS(sidx);
>
> @@ -499,7 +530,7 @@ find_block:
> }
>
> if (fallback) {
> - sidx = ALIGN(fallback - 1, step);
> + sidx = align_idx(bdata, fallback - 1, step);
> fallback = 0;
> goto find_block;
> }
>




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