Comment 0 for bug 1572562

The following error message could be observed during the kernel
building stress test of the command: "./parallel-73670.sh -r 2 -k 40"
That means building 40 kernels in the same time with 2 rounds.

Bad access happens when we read page->mapping->flags, and
page->mapping is a pointer to anon_vma which is already freed
in the do_exit path.

==================================================================
BUG: KASan: out of bounds access in isolate_migratepages_range+0x663/0xb30 at addr ffff880279cc76d1
Read of size 8 by task cc1/27473
=============================================================================
BUG anon_vma (Not tainted): kasan: bad access detected
-----------------------------------------------------------------------------

Disabling lock debugging due to kernel taint
INFO: Allocated in anon_vma_prepare+0x189/0x250 age=7323 cpu=16 pid=31029
        __slab_alloc+0x4f8/0x560
        kmem_cache_alloc+0x18b/0x1e0
        anon_vma_prepare+0x189/0x250
        do_wp_page+0x837/0xb10
        handle_mm_fault+0x884/0x1160
        __do_page_fault+0x218/0x750
        do_page_fault+0x1a/0x70
        page_fault+0x28/0x30
INFO: Freed in __put_anon_vma+0x69/0xe0 age=8588 cpu=4 pid=29418
        __slab_free+0x2ab/0x3f0
        kmem_cache_free+0x1c1/0x200
        __put_anon_vma+0x69/0xe0
        unlink_anon_vmas+0x2a8/0x320
        free_pgtables+0x50/0x1c0
        exit_mmap+0xca/0x1e0
        mmput+0x82/0x1b0
        do_exit+0x391/0x1060
        do_group_exit+0x86/0x130
        SyS_exit_group+0x1d/0x20
        system_call_fastpath+0x1a/0x1f
INFO: Slab 0xffffea0009e73100 objects=43 used=30 fp=0xffff880279cc67a8 flags=0x2ffff0000004080
INFO: Object 0xffff880279cc7658 @offset=13912 fp=0xffff880279cc7c38

Bytes b4 ffff880279cc7648: 10 00 00 00 5b 17 00 00 ef 25 6b 03 01 00 00 00 ....[....%k.....
Object ffff880279cc7658: 58 76 cc 79 02 88 ff ff 00 00 00 00 00 00 00 00 Xv.y............
Object ffff880279cc7668: 00 00 00 00 5a 5a 5a 5a 70 76 cc 79 02 88 ff ff ....ZZZZpv.y....
Object ffff880279cc7678: 70 76 cc 79 02 88 ff ff 01 00 00 00 03 00 00 00 pv.y............
Object ffff880279cc7688: 58 76 cc 79 02 88 ff ff b8 2a 20 31 02 88 ff ff Xv.y.....* 1....
CPU: 8 PID: 27473 Comm: cc1 Tainted: G B 3.13.0-76-generic #120hf00073670v20160120b0h5d3e6ab
Hardware name: Cisco Systems Inc UCSC-C220-M3L/UCSC-C220-M3L, BIOS C220M3.2.0.3.0.080120140402 08/01/2014
 ffffea0009e73100 ffff880736bbf750 ffffffff81a6e195 ffff8804e881b840
 ffff880736bbf780 ffffffff81244c1d ffff8804e881b840 ffffea0009e73100
 ffff880279cc7658 ffffea001aa99c98 ffff880736bbf7a8 ffffffff8124ad66
Call Trace:
 [<ffffffff81a6e195>] dump_stack+0x45/0x56
 [<ffffffff81244c1d>] print_trailer+0xfd/0x170
 [<ffffffff8124ad66>] object_err+0x36/0x40
 [<ffffffff8124cd29>] kasan_report_error+0x1e9/0x3a0
 [<ffffffff8125d9f8>] ? memcg_check_events+0x28/0x380
 [<ffffffff81221c2d>] ? rmap_walk+0x32d/0x340
 [<ffffffff8124d390>] kasan_report+0x40/0x50
 [<ffffffff81205ee3>] ? isolate_migratepages_range+0x663/0xb30
 [<ffffffff8124c019>] __asan_load8+0x69/0xa0
 [<ffffffff81205ee3>] isolate_migratepages_range+0x663/0xb30
 [<ffffffff811dc5e7>] ? zone_watermark_ok+0x57/0x70
 [<ffffffff812067c6>] compact_zone+0x416/0x700
 [<ffffffff81206b45>] compact_zone_order+0x95/0x100
 [<ffffffff81207002>] try_to_compact_pages+0x102/0x1a0
 [<ffffffff811e21e6>] __alloc_pages_direct_compact+0x96/0x290
 [<ffffffff811e2d5e>] __alloc_pages_nodemask+0x97e/0xc40
 [<ffffffff8123ce24>] alloc_pages_vma+0xb4/0x200
 [<ffffffff812572ca>] do_huge_pmd_anonymous_page+0x13a/0x490
 [<ffffffff8120f072>] ? do_numa_page+0x192/0x200
 [<ffffffff81210c07>] handle_mm_fault+0x267/0x1160
 [<ffffffff81a7d028>] __do_page_fault+0x218/0x750
 [<ffffffff8121aead>] ? do_mmap_pgoff+0x47d/0x500
 [<ffffffff811fd699>] ? vm_mmap_pgoff+0xa9/0xd0
 [<ffffffff81a7d57a>] do_page_fault+0x1a/0x70
 [<ffffffff81a785a8>] page_fault+0x28/0x30
Memory state around the buggy address:
 ffff880279cc7580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff880279cc7600: fc fc fc fc fc fc fc fc fc fc fc 00 00 00 00 00
>ffff880279cc7680: 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc
                                                 ^
 ffff880279cc7700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff880279cc7780: fc fc fc fc fc fc fc fc fc fc 00 00 00 00 00 00
==================================================================

gavin@rotom:~/ddebs/ddebs-3.13.0-76.120hf00073670v20160120b0h5d3e6ab$ addr2line 0xffffffff81205ee3 -e usr/lib/debug/boot/vmlinux-3.13.0-76-generic -fi
constant_test_bit
/home/gavin/ubuntu-trusty-amd64/arch/x86/include/asm/bitops.h:313
mapping_balloon
/home/gavin/ubuntu-trusty-amd64/include/linux/pagemap.h:69
__is_movable_balloon_page
/home/gavin/ubuntu-trusty-amd64/include/linux/balloon_compaction.h:131
balloon_page_movable
/home/gavin/ubuntu-trusty-amd64/include/linux/balloon_compaction.h:156
isolate_migratepages_range
/home/gavin/ubuntu-trusty-amd64/mm/compaction.c:554

>8------------------8<
/home/gavin/ubuntu-trusty-amd64/arch/x86/include/asm/bitops.h:313
310 static __always_inline int constant_test_bit(long nr, const volatile unsigned long *addr)
311 {
312 return ((1UL << (nr & (BITS_PER_LONG-1))) &
313 (addr[nr >> _BITOPS_LONG_SHIFT])) != 0;
314 }