Re: [PATCH v2] mm/rmap: fix BUG at rmap_walk

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

Hi Bob,
On Thu, Dec 19, 2013 at 12:16:22PM +0800, Bob Liu wrote:
>On Thu, Dec 19, 2013 at 11:45 AM, Wanpeng Li <liwanp@linux.vnet.ibm.com> wrote:
>> page_get_anon_vma() called in page_referenced_anon() will lock and increase
>> the refcount of anon_vma, page won't be locked for anonymous page if the page
>> is not locked by the caller. This patch fix the BUG_ON by reuse referenced
>> field in page_referenced_arg to capture locked anonymous page for page_referenced(),
>> if the anonymous page is locked by the caller, the referenced field will remember
>> it, rmap_walk_anon will check if page locked if caller lock it.
>>
>
>Better commit log, please.
>This bug is introduced by  commit 37f093cdf(mm/rmap: use rmap_walk()
>in page_referenced()).

Thanks.

>PageLocked is not required by page_referenced_anon() and there is not
>any assertion before, commit 37f093cdf introduced this extra BUG_ON()

There are two callsites shrink_active_list and page_check_references()
of page_referenced(). shrink_active_list and its callee won't lock anonymous
page, however, page_check_references() is called with anonymous page
lock held in shrink_page_list. So page_check_references case need
specail handling.

>checking for anon page by mistake.
>
>> [  588.698828] kernel BUG at mm/rmap.c:1663!
>> [  588.699380] invalid opcode: 0000 [#2] PREEMPT SMP DEBUG_PAGEALLOC
>> [  588.700347] Dumping ftrace buffer:
>> [  588.701186]    (ftrace buffer empty)
>> [  588.702062] Modules linked in:
>> [  588.702759] CPU: 0 PID: 4647 Comm: kswapd0 Tainted: G      D W    3.13.0-rc4-next-20131218-sasha-00012-g1962367-dirty #4155
>> [  588.704330] task: ffff880062bcb000 ti: ffff880062450000 task.ti: ffff880062450000
>> [  588.705507] RIP: 0010:[<ffffffff81289c80>]  [<ffffffff81289c80>] rmap_walk+0x10/0x50
>> [  588.706800] RSP: 0018:ffff8800624518d8  EFLAGS: 00010246
>> [  588.707515] RAX: 000fffff80080048 RBX: ffffea00000227c0 RCX: 0000000000000000
>> [  588.707515] RDX: 0000000000000000 RSI: ffff8800624518e8 RDI: ffffea00000227c0
>> [  588.707515] RBP: ffff8800624518d8 R08: ffff8800624518e8 R09: 0000000000000000
>> [  588.707515] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800624519d8
>> [  588.707515] R13: 0000000000000000 R14: ffffea00000227e0 R15: 0000000000000000
>> [  588.707515] FS:  0000000000000000(0000) GS:ffff880065200000(0000) knlGS:0000000000000000
>> [  588.707515] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> [  588.707515] CR2: 00007fec40cbe0f8 CR3: 00000000c2382000 CR4: 00000000000006f0
>> [  588.707515] Stack:
>> [  588.707515]  ffff880062451958 ffffffff81289f4b ffff880062451918 ffffffff81289f80
>> [  588.707515]  0000000000000000 0000000000000000 ffffffff8128af60 0000000000000000
>> [  588.707515]  0000000000000024 0000000000000000 0000000000000000 0000000000000286
>> [  588.707515] Call Trace:
>> [  588.707515]  [<ffffffff81289f4b>] page_referenced+0xcb/0x100
>> [  588.707515]  [<ffffffff81289f80>] ? page_referenced+0x100/0x100
>> [  588.707515]  [<ffffffff8128af60>] ? invalid_page_referenced_vma+0x170/0x170
>> [  588.707515]  [<ffffffff81264302>] shrink_active_list+0x212/0x330
>> [  588.707515]  [<ffffffff81260e23>] ? inactive_file_is_low+0x33/0x50
>> [  588.707515]  [<ffffffff812646f5>] shrink_lruvec+0x2d5/0x300
>> [  588.707515]  [<ffffffff812647b6>] shrink_zone+0x96/0x1e0
>> [  588.707515]  [<ffffffff81265b06>] kswapd_shrink_zone+0xf6/0x1c0
>> [  588.707515]  [<ffffffff81265f43>] balance_pgdat+0x373/0x550
>> [  588.707515]  [<ffffffff81266d63>] kswapd+0x2f3/0x350
>> [  588.707515]  [<ffffffff81266a70>] ? perf_trace_mm_vmscan_lru_isolate_template+0x120/0x120
>> [  588.707515]  [<ffffffff8115c9c5>] kthread+0x105/0x110
>> [  588.707515]  [<ffffffff8115c8c0>] ? set_kthreadd_affinity+0x30/0x30
>> [  588.707515]  [<ffffffff843a6a7c>] ret_from_fork+0x7c/0xb0
>> [  588.707515]  [<ffffffff8115c8c0>] ? set_kthreadd_affinity+0x30/0x30
>> [  588.707515] Code: c0 48 83 c4 18 89 d0 5b 41 5c 41 5d 41 5e 41 5f c9 c3 66 0f 1f 84
>> 00 00 00 00 00 55 48 89 e5 66 66 66 66 90 48 8b 07 a8 01 75 10 <0f> 0b 66 0f 1f 44 00 0
>> 0 eb fe 66 0f 1f 44 00 00 f6 47 08 01 74
>> [  588.707515] RIP  [<ffffffff81289c80>] rmap_walk+0x10/0x50
>> [  588.707515]  RSP <ffff8800624518d8>
>>
>> Reported-by: Sasha Levin <sasha.levin@oracle.com>
>> Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
>> ---
>>  mm/ksm.c  |  5 +++++
>>  mm/rmap.c | 20 ++++++++++++++++++--
>>  2 files changed, 23 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/ksm.c b/mm/ksm.c
>> index c9a28dd..76d96df 100644
>> --- a/mm/ksm.c
>> +++ b/mm/ksm.c
>> @@ -1899,6 +1899,11 @@ int rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
>>         int search_new_forks = 0;
>>
>>         VM_BUG_ON(!PageKsm(page));
>> +
>> +       /*
>> +        * Rely on the page lock to protect against concurrent modifications
>> +        * to that page's node of the stable tree.
>> +        */
>>         VM_BUG_ON(!PageLocked(page));
>>
>>         stable_node = page_stable_node(page);
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index d792e71..db83961 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -769,6 +769,10 @@ int page_referenced(struct page *page,
>>         struct page_referenced_arg pra = {
>>                 .mapcount = page_mapcount(page),
>>                 .memcg = memcg,
>> +               /*
>> +                * reuse referenced field for the locked anonymous page check
>> +                */
>> +               .referenced = is_locked && PageAnon(page) && !PageKsm(page),
>>         };
>>         struct rmap_walk_control rwc = {
>>                 .rmap_one = page_referenced_one,
>> @@ -1587,6 +1591,12 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
>>         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
>>         struct anon_vma_chain *avc;
>>         int ret = SWAP_AGAIN;
>> +       struct page_referenced_arg *pra = rwc->arg;
>> +
>> +       if (pra->referenced) {
>> +               VM_BUG_ON(!PageLocked(page));
>> +               pra->referenced = 0;
>> +       }
>>
> 
>I don't this is needed.

I think I have aready explained why need it. ;-)

Regards,
Wanpeng Li 

>
>-- 
>Regards,
>--Bob

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