Re: NULL pointer dereference in the kernel 3.10

["Hillf Danton" <hillf.zj@alibaba-inc.com>]

On April 08, 2017 9:40 PM zhong Jiang wrote: 
> 
> when runing the stabile docker cases in the vm.   The following issue will come up.
> 
> #40 [ffff8801b57ffb30] async_page_fault at ffffffff8165c9f8
>     [exception RIP: down_read_trylock+5]
>     RIP: ffffffff810aca65  RSP: ffff8801b57ffbe8  RFLAGS: 00010202
>     RAX: 0000000000000000  RBX: ffff88018ae858c1  RCX: 0000000000000000
>     RDX: 0000000000000000  RSI: 0000000000000000  RDI: 0000000000000008
>     RBP: ffff8801b57ffc10   R8: ffffea0006903de0   R9: ffff8800b3c61810
>     R10: 00000000000022cb  R11: 0000000000000000  R12: ffff88018ae858c0
>     R13: ffffea0006903dc0  R14: 0000000000000008  R15: ffffea0006903dc0
>     ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0000
> #41 [ffff8801b57ffbe8] page_lock_anon_vma_read at ffffffff811b241c
> #42 [ffff8801b57ffc18] page_referenced at ffffffff811b26a7
> #43 [ffff8801b57ffc90] shrink_active_list at ffffffff8118d634
> #44 [ffff8801b57ffd48] balance_pgdat at ffffffff8118f088
> #45 [ffff8801b57ffe20] kswapd at ffffffff8118f633
> #46 [ffff8801b57ffec8] kthread at ffffffff810a795f
> #47 [ffff8801b57fff50] ret_from_fork at ffffffff81665398
> crash> struct page.mapping ffffea0006903dc0
>   mapping = 0xffff88018ae858c1
> crash> struct anon_vma 0xffff88018ae858c0
> struct anon_vma {
>   root = 0x0,
>   rwsem = {
>     count = 0,
>     wait_lock = {
>       raw_lock = {
>         {
>           head_tail = 1,
>           tickets = {
>             head = 1,
>             tail = 0
>           }
>         }
>       }
>     },
>     wait_list = {
>       next = 0x0,
>       prev = 0x0
>     }
>   },
>   refcount = {
>     counter = 0
>   },
>   rb_root = {
>     rb_node = 0x0
>   }
> }
> 
> This maks me wonder,  the anon_vma do not come from slab structure.
> and the content is abnormal. IMO,  At least anon_vma->root will not NULL.
> The issue can be reproduced every other week.
> 
Check please if commit 
624483f3ea8 ("mm: rmap: fix use-after-free in __put_anon_vma")
is included in the 3.10 you are running.

btw, why not run the mainline?

Hillf


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