On Thu, Mar 16, 2017 at 05:09:48PM +0800, zhong jiang wrote:
> On 2017/3/16 16:42, Vladimir Davydov wrote:
> > On Thu, Mar 16, 2017 at 03:45:34PM +0800, zhong jiang wrote:
> >> Hi, Vladimir
> >>
> >> I find upstream 414e2fb8ce5a ("rmap: fix theoretical race between do_wp_page and shrink_active_list ")
> >> fix the bug maybe is the same as the following issue, but I'm not sure.
> > It looks like in your case shrink_active_list() ran into a page with
> > page->mapping set to PAGE_MAPPING_ANON, which made page_referenced()
> > call page_referenced_anon(), which in turn called
> > page_lock_anon_vma_read(), which hit the bug trying to dereference
> > (page->mapping - PAGE_MAPPING_ANON) = NULL.
> Yes, That is what we think.
> > Theoretically, this could happen if page->mapping was updated
> > non-atomically by page_move_anon_rmap(), which is the case the commit
> > you mentioned fixes. However, I find it unlikely to happen on x86 with
> > any sane compiler: on x86 it should be cheaper to first load the result
> > (PAGE_MAPPING_ANON + addr in this case) to a register and only then
> > store it in memory as a whole (page->mapping). To be sure, you should
> > check assembly of page_move_anon_rmap() if it updates page->mapping
> > non-atomically.
> The following is the assembly code.
>
> (gdb) disassemble page_move_anon_rmap
> Dump of assembler code for function page_move_anon_rmap:
> 0xffffffff811a4e10 <+0>: callq 0xffffffff8164d9c0 <__fentry__>
> 0xffffffff811a4e15 <+5>: mov 0x88(%rsi),%rax
Load vma->anon_vma address to RAX.
> 0xffffffff811a4e1c <+12>: push %rbp
> 0xffffffff811a4e1d <+13>: mov %rsp,%rbp
> 0xffffffff811a4e20 <+16>: add $0x1,%rax
Add PAGE_MAPPING_ANON to RAX.
> 0xffffffff811a4e24 <+20>: mov %rax,0x8(%rdi)
Move the result to page->mapping.
This is atomic, so the commit you mentioned won't help, unfortunately.
> 0xffffffff811a4e28 <+24>: pop %rbp
> 0xffffffff811a4e29 <+25>: retq
> End of assembler dump.
> (gdb)
> >> 9381.005212] CPU: 3 PID: 12737 Comm: docker-runc Tainted: G OE ---- ------- 3.10.0-327.36.58.4.x86_64 #1
> >> [19381.005212] Hardware name: OpenStack Foundation OpenStack Nova, BIOS rel-1.8.1-0-g4adadbd-20160826_044443-hghoulaslx112 04/01/2014
> >> [19381.005212] task: ffff880002938000 ti: ffff880232254000 task.ti: ffff880232254000
> >> [19381.005212] RIP: 0010:[<ffffffff810aca65>] [<ffffffff810aca65>] down_read_trylock+0x5/0x50
> >> [19381.005212] RSP: 0018:ffff8802322576c0 EFLAGS: 00010202
> >> [19381.005212] RAX: 0000000000000000 RBX: ffff880230cabbc0 RCX: 0000000000000000
> >> [19381.005212] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000008
> >> [19381.005212] RBP: ffff8802322576e8 R08: ffffea00083725a0 R09: ffff8800b185b408
> >> [19381.005212] R10: 0000000000000000 R11: fff00000fe000000 R12: ffff880230cabbc1
> >> [19381.005212] R13: ffffea0008372580 R14: 0000000000000008 R15: ffffea0008372580
> >> [19381.005212] FS: 00007f66aea00700(0000) GS:ffff88023ed80000(0000) knlGS:0000000000000000
> >> [19381.005212] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> [19381.005212] CR2: 0000000000000008 CR3: 0000000231be8000 CR4: 00000000001407e0
> >> [19381.005212] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> [19381.005212] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> >> [19381.018017] Stack:
> >> [19381.018017] ffffffff811b22b5 ffffea0008372580 0000000000000000 0000000000000004
> >> [19381.018017] 0000000000000001 ffff880232257760 ffffffff811b2537 ffff8800b18ab1c0
> >> [19381.018017] 00000007fcd103e2 ffff8802322577b0 0000000100000000 00000007fcd0fbe6
> >> [19381.018017] Call Trace:
> >> [19381.018017] [<ffffffff811b22b5>] ? page_lock_anon_vma_read+0x55/0x110
> >> [19381.018017] [<ffffffff811b2537>] page_referenced+0x1c7/0x350
> >> [19381.018017] [<ffffffff8118d634>] shrink_active_list+0x1e4/0x400
> >> [19381.018017] [<ffffffff8118dd0d>] shrink_lruvec+0x4bd/0x770
> >> [19381.018017] [<ffffffff8118e036>] shrink_zone+0x76/0x1a0
> >> [19381.018017] [<ffffffff8118e530>] do_try_to_free_pages+0xe0/0x3f0
> >> [19381.018017] [<ffffffff8118e93c>] try_to_free_pages+0xfc/0x180
> >> [19381.018017] [<ffffffff81182218>] __alloc_pages_nodemask+0x818/0xcc0
> >> [19381.018017] [<ffffffff811cabfa>] alloc_pages_vma+0x9a/0x150
> >> [19381.018017] [<ffffffff811e0346>] do_huge_pmd_wp_page+0x106/0xb60
> >> [19381.018017] [<ffffffffa01c27d0>] ? dm_get_queue_limits+0x30/0x30 [dm_mod]
> >> [19381.018017] [<ffffffff811a6518>] handle_mm_fault+0x638/0xfa0
> >> [19381.018017] [<ffffffff81313cf2>] ? radix_tree_lookup_slot+0x22/0x50
> >> [19381.018017] [<ffffffff8117771e>] ? __find_get_page+0x1e/0xa0
> >> [19381.018017] [<ffffffff81160097>] ? rtos_hungtask_acquired+0x57/0x140
> >> [19381.018017] [<ffffffff81660435>] __do_page_fault+0x145/0x490
> >> [19381.018017] [<ffffffff81660843>] trace_do_page_fault+0x43/0x110
> >> [19381.018017] [<ffffffff8165fef9>] do_async_page_fault+0x29/0xe0
> >> [19381.018017] [<ffffffff8165c538>] async_page_fault+0x28/0x30
> >> [19381.018017] [<ffffffff8131af79>] ? copy_user_enhanced_fast_string+0x9/0x20
> >> [19381.018017] [<ffffffff81207c9c>] ? poll_select_copy_remaining+0xfc/0x150
> >> [19381.018017] [<ffffffff81208c2c>] SyS_select+0xcc/0x110
> >> [19381.018017] [<ffffffff81664ff3>] system_call_fastpath+0x16/0x1b
> > .
> >
>
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