On Tue, May 5, 2015 at 2:34 AM, Laura Abbott <labbott@xxxxxxxxxx> wrote: > On 05/04/2015 02:41 AM, Hui Zhu wrote: >> >> 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..434730b 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_present(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); >> > > I think you want to use pfn_valid_within instead of pfn_present. Thanks. I will post a new version for it. Best, Hui > > Thanks, > Laura > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>