• Hui Zhu's avatar
    CMA: page_isolation: check buddy before accessing it · 1ae7013d
    Hui Zhu authored
    I had an issue:
    
        Unable to handle kernel NULL pointer dereference at virtual address 0000082a
        pgd = cc970000
        [0000082a] *pgd=00000000
        Internal error: Oops: 5 [#1] PREEMPT SMP ARM
        PC is at get_pageblock_flags_group+0x5c/0xb0
        LR is at unset_migratetype_isolate+0x148/0x1b0
        pc : [<c00cc9a0>]    lr : [<c0109874>]    psr: 80000093
        sp : c7029d00  ip : 00000105  fp : c7029d1c
        r10: 00000001  r9 : 0000000a  r8 : 00000004
        r7 : 60000013  r6 : 000000a4  r5 : c0a357e4  r4 : 00000000
        r3 : 00000826  r2 : 00000002  r1 : 00000000  r0 : 0000003f
        Flags: Nzcv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment user
        Control: 10c5387d  Table: 2cb7006a  DAC: 00000015
        Backtrace:
            get_pageblock_flags_group+0x0/0xb0
            unset_migratetype_isolate+0x0/0x1b0
            undo_isolate_page_range+0x0/0xdc
            __alloc_contig_range+0x0/0x34c
            alloc_contig_range+0x0/0x18
    
    This issue is because when calling 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 at boot time (not in buddy system).  So add a
    check before accessing it.
    
    [akpm@linux-foundation.org: use conventional code layout]
    Signed-off-by: default avatarHui Zhu <zhuhui@xiaomi.com>
    Suggested-by: default avatarLaura Abbott <labbott@redhat.com>
    Suggested-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    1ae7013d
page_isolation.c 8.74 KB