On Tue, May 05, 2015 at 11:22:59AM +0800, Hui Zhu wrote:
> Change pfn_present to pfn_valid_within according to the review of Laura.
>
> I got a issue:
> [ 214.294917] Unable to handle kernel NULL pointer dereference at virtual address 0000082a
> [ 214.303013] pgd = cc970000
> [ 214.305721] [0000082a] *pgd=00000000
> [ 214.309316] Internal error: Oops: 5 [#1] PREEMPT SMP ARM
> [ 214.335704] PC is at get_pageblock_flags_group+0x5c/0xb0
> [ 214.341030] LR is at unset_migratetype_isolate+0x148/0x1b0
> [ 214.346523] pc : [<c00cc9a0>] lr : [<c0109874>] psr: 80000093
> [ 214.346523] sp : c7029d00 ip : 00000105 fp : c7029d1c
> [ 214.358005] r10: 00000001 r9 : 0000000a r8 : 00000004
> [ 214.363231] r7 : 60000013 r6 : 000000a4 r5 : c0a357e4 r4 : 00000000
> [ 214.369761] r3 : 00000826 r2 : 00000002 r1 : 00000000 r0 : 0000003f
> [ 214.376291] Flags: Nzcv IRQs off FIQs on Mode SVC_32 ISA ARM Segment user
> [ 214.383516] Control: 10c5387d Table: 2cb7006a DAC: 00000015
> [ 214.949720] Backtrace:
> [ 214.952192] [<c00cc944>] (get_pageblock_flags_group+0x0/0xb0) from [<c0109874>] (unset_migratetype_isolate+0x148/0x1b0)
> [ 214.962978] r7:60000013 r6:c0a357c0 r5:c0a357e4 r4:c1555000
> [ 214.968693] [<c010972c>] (unset_migratetype_isolate+0x0/0x1b0) from [<c0109adc>] (undo_isolate_page_range+0xd0/0xdc)
> [ 214.979222] [<c0109a0c>] (undo_isolate_page_range+0x0/0xdc) from [<c00d097c>] (__alloc_contig_range+0x254/0x34c)
> [ 214.989398] r9:000abc00 r8:c7028000 r7:000b1f53 r6:000b3e00 r5:00000005
> r4:c7029db4
> [ 214.997308] [<c00d0728>] (__alloc_contig_range+0x0/0x34c) from [<c00d0a88>] (alloc_contig_range+0x14/0x18)
> [ 215.006973] [<c00d0a74>] (alloc_contig_range+0x0/0x18) from [<c0398148>] (dma_alloc_from_contiguous_addr+0x1ac/0x304)
>
> This issue is because when call unset_migratetype_isolate to unset a part
> of CMA memory, it try to access the buddy page to get its status:
> if (order >= pageblock_order) {
> page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1);
> buddy_idx = __find_buddy_index(page_idx, order);
> buddy = page + (buddy_idx - page_idx);
>
> if (!is_migrate_isolate_page(buddy)) {
> But the begin addr of this part of CMA memory is very close to a part of
> memory that is reserved in the boot time (not in buddy system).
> So add a check before access it.
>
> Signed-off-by: Hui Zhu <zhuhui@xxxxxxxxxx>
> ---
> mm/page_isolation.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 755a42c..eb22d1f 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -101,7 +101,8 @@ void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> buddy_idx = __find_buddy_index(page_idx, order);
> buddy = page + (buddy_idx - page_idx);
>
> - if (!is_migrate_isolate_page(buddy)) {
> + if (!pfn_valid_within(page_to_pfn(buddy))
> + || !is_migrate_isolate_page(buddy)) {
> __isolate_free_page(page, order);
> kernel_map_pages(page, (1 << order), 1);
> set_page_refcounted(page);
Hello,
This isolation is for merging buddy pages. If buddy is not valid, we
don't need to isolate page, because we can't merge them.
I think that correct code would be:
pfn_valid_within(page_to_pfn(buddy)) &&
!is_migrate_isolate_page(buddy)
But, isolation and free here is safe operation so your code will work
fine.
Thanks.
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