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Date: Mon, 17 Mar 2014 18:58:14 -0400
From: Sasha Levin <sasha.levin@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>, Bob Liu <bob.liu@...cle.com>
CC: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
Rik van Riel <riel@...hat.com>, joern@...fs.org,
Michel Lespinasse <walken@...gle.com>
Subject: Re: [PATCH 1/3] mm: munlock: fix a bug where THP tail page is encountered
On 03/17/2014 06:20 PM, Vlastimil Babka wrote:
> On 17.3.2014 22:08, Sasha Levin wrote:
>> On 03/17/2014 08:38 AM, Vlastimil Babka wrote:
>>> On 03/15/2014 04:06 AM, Sasha Levin wrote:
>>>> On 03/14/2014 07:55 PM, Sasha Levin wrote:
>>>>> On 12/17/2013 08:00 AM, Vlastimil Babka wrote:
>>>>>> From: Vlastimil Babka<vbabka@...e.cz>
>>>>>> Date: Fri, 13 Dec 2013 14:25:21 +0100
>>>>>> Subject: [PATCH 1/3] mm: munlock: fix a bug where THP tail page is encountered
>>>>>>
>>>>>> Since commit ff6a6da60 ("mm: accelerate munlock() treatment of THP pages")
>>>>>> munlock skips tail pages of a munlocked THP page. However, when the head page
>>>>>> already has PageMlocked unset, it will not skip the tail pages.
>>>>>>
>>>>>> Commit 7225522bb ("mm: munlock: batch non-THP page isolation and
>>>>>> munlock+putback using pagevec") has added a PageTransHuge() check which
>>>>>> contains VM_BUG_ON(PageTail(page)). Sasha Levin found this triggered using
>>>>>> trinity, on the first tail page of a THP page without PageMlocked flag.
>>>>>>
>>>>>> This patch fixes the issue by skipping tail pages also in the case when
>>>>>> PageMlocked flag is unset. There is still a possibility of race with THP page
>>>>>> split between clearing PageMlocked and determining how many pages to skip.
>>>>>> The race might result in former tail pages not being skipped, which is however
>>>>>> no longer a bug, as during the skip the PageTail flags are cleared.
>>>>>>
>>>>>> However this race also affects correctness of NR_MLOCK accounting, which is to
>>>>>> be fixed in a separate patch.
>>>>>
>>>>> I've hit the same thing again, on the latest -next, this time with a different trace:
>>>>>
>>>>> [ 539.199120] page:ffffea0013249a80 count:0 mapcount:1 mapping: (null) index:0x0
>>>>> [ 539.200429] page flags: 0x12fffff80008000(tail)
>>>>> [ 539.201167] ------------[ cut here ]------------
>>>>> [ 539.201889] kernel BUG at include/linux/page-flags.h:415!
>>>>> [ 539.202859] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
>>>>> [ 539.204588] Dumping ftrace buffer:
>>>>> [ 539.206415] (ftrace buffer empty)
>>>>> [ 539.207022] Modules linked in:
>>>>> [ 539.207503] CPU: 3 PID: 18262 Comm: trinity-c228 Tainted: G W 3.14.0-rc6-next-20140313-sasha-00010-gb8c1db1-dirty #217
>>>>> [ 539.209012] task: ffff880627b10000 ti: ffff8805a44c2000 task.ti: ffff8805a44c2000
>>>>> [ 539.209989] RIP: munlock_vma_pages_range+0x93/0x1d0 (include/linux/page-flags.h:415 mm/mlock.c:494)
>>>>> [ 539.210263] RSP: 0000:ffff8805a44c3e08 EFLAGS: 00010246
>>>>> [ 539.210263] RAX: ffff88052ae126a0 RBX: 000000000006a000 RCX: 0000000000000099
>>>>> [ 539.210263] RDX: 0000000000000000 RSI: ffff880627b10cf0 RDI: 0000000004c926a0
>>>>> [ 539.210263] RBP: ffff8805a44c3ec8 R08: 0000000000000001 R09: 0000000000000001
>>>>> [ 539.210263] R10: 0000000000000001 R11: 0000000000000001 R12: ffffea0013249a80
>>>>> [ 539.210263] R13: ffff88039dc95a00 R14: 000000000006b000 R15: ffff8805a44c3e94
>>>>> [ 539.210263] FS: 00007fd6ce14a700(0000) GS:ffff88042b800000(0000) knlGS:0000000000000000
>>>>> [ 539.210263] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>>>> [ 539.210263] CR2: 00007fd6ce0ef6ac CR3: 00000006025cd000 CR4: 00000000000006a0
>>>>> [ 539.210263] DR0: 0000000000698000 DR1: 0000000000000000 DR2: 0000000000000000
>>>>> [ 539.210263] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
>>>>> [ 539.210263] Stack:
>>>>> [ 539.210263] 0000000000000000 0000000000000000 00018805a44c3e38 0000000000000000
>>>>> [ 539.210263] 0000000000000000 ffff88039dc95a00 00000000a44c3e88 0000000000000000
>>>>> [ 539.210263] 00ff8805a44c3e58 ffff880528f0a0f0 ffff8805a44c3eb8 ffff88039dc95a00
>>>>> [ 539.210263] Call Trace:
>>>>> [ 539.210263] do_munmap+0x1d2/0x360 (mm/internal.h:168 mm/mmap.c:2547)
>>>>> [ 539.210263] ? down_write+0xa6/0xc0 (kernel/locking/rwsem.c:51)
>>>>> [ 539.210263] ? vm_munmap+0x46/0x80 (mm/mmap.c:2571)
>>>>> [ 539.210263] vm_munmap+0x54/0x80 (mm/mmap.c:2572)
>>>>> [ 539.210263] SyS_munmap+0x2c/0x40 (mm/mmap.c:2577)
>>>>> [ 539.210263] tracesys+0xdd/0xe2 (arch/x86/kernel/entry_64.S:749)
>>>>> [ 539.210263] Code: ff 49 89 c4 48 85 c0 0f 84 f3 00 00 00 48 3d 00 f0 ff ff 0f 87 e7 00 00 00 48 8b 00 66 85 c0 79 17 31 f6 4c 89 e7 e8 4d d2 fc ff <0f> 0b 0f 1f 00 eb fe 66 0f 1f 44 00 00 49 8b 04 24 f6 c4 40 74
>>>>> [ 539.210263] RIP munlock_vma_pages_range+0x93/0x1d0 (include/linux/page-flags.h:415 mm/mlock.c:494)
>>>>> [ 539.210263] RSP <ffff8805a44c3e08>
>>>>> [ 539.236666] ---[ end trace 4e90dc9141579181 ]---
>>>>>
>>>>>
>>>>> Thanks,
>>>>> Sasha
>>>>
>>>> And another related trace:
>>>>
>>>> [ 741.192502] kernel BUG at mm/mlock.c:528!
>>>> [ 741.193088] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
>>>> [ 741.194177] Dumping ftrace buffer:
>>>> [ 741.194645] (ftrace buffer empty)
>>>> [ 741.195109] Modules linked in:
>>>> [ 741.195728] CPU: 23 PID: 19908 Comm: trinity-c264 Tainted: G W 3.14.0-rc6-next-20140314-sasha-00012-g5590866 #219
>>>> [ 741.197549] task: ffff88061fc2b000 ti: ffff8805decb8000 task.ti: ffff8805decb8000
>>>> [ 741.198548] RIP: munlock_vma_pages_range+0x176/0x1d0 (mm/mlock.c:528)
>>>> [ 741.199754] RSP: 0018:ffff8805decb9e08 EFLAGS: 00010206
>>>> [ 741.200085] RAX: 00000000000001ff RBX: 0000000000111000 RCX: 0000000000000000
>>>> [ 741.200085] RDX: 0000000000000111 RSI: ffffffff81295fdd RDI: ffffffff84490705
>>>> [ 741.200085] RBP: ffff8805decb9ec8 R08: 0000000000000000 R09: 0000000000000000
>>>> [ 741.200085] R10: 0000000000000001 R11: 0000000000000000 R12: fffffffffffffff2
>>>> [ 741.200085] R13: ffff880221044e00 R14: 0000000000112000 R15: ffff8805decb9e94
>>>> [ 741.200085] FS: 00007f4bec6bc700(0000) GS:ffff88082ba00000(0000) knlGS:0000000000000000
>>>> [ 741.200085] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>>> [ 741.200085] CR2: 0000000003109a98 CR3: 00000005decaf000 CR4: 00000000000006a0
>>>> [ 741.200085] Stack:
>>>> [ 741.200085] 0000000000000000 0000000000000000 00018805decb9e38 0000000000000000
>>>> [ 741.200085] 0000000000000000 ffff880221044e00 00000000decb9e88 0000000000000000
>>>> [ 741.200085] 00ff8805decb9e58 ffff880ff376f450 ffff8805decb9eb8 ffff880221044e00
>>>> [ 741.200085] Call Trace:
>>>> [ 741.200085] do_munmap+0x1d2/0x360 (mm/internal.h:168 mm/mmap.c:2547)
>>>> [ 741.200085] ? down_write+0xa6/0xc0 (kernel/locking/rwsem.c:51)
>>>> [ 741.200085] ? vm_munmap+0x46/0x80 (mm/mmap.c:2571)
>>>> [ 741.200085] vm_munmap+0x54/0x80 (mm/mmap.c:2572)
>>>> [ 741.200085] SyS_munmap+0x2c/0x40 (mm/mmap.c:2577)
>>>> [ 741.200085] tracesys+0xdd/0xe2 (arch/x86/kernel/entry_64.S:749)
>>>> [ 741.200085] Code: fd ff ff 4c 89 e6 48 89 c3 48 8d bd 40 ff ff ff e8 80 fa ff ff eb 2f 66 0f 1f 44 00 00 8b 45 cc 48 89 da 48 c1 ea 0c 85 d0 74 12 <0f> 0b 0f 1f 84 00 00 00 00 00 eb fe 66 0f 1f 44 00 00 ff c0 48
>>>> [ 741.200085] RIP munlock_vma_pages_range+0x176/0x1d0 (mm/mlock.c:528)
>>>> [ 741.200085] RSP <ffff8805decb9e08>
>>>
>>> Sigh, again? I really wonder what is it this time :)
>>> Please try this debug patch, hopefully we learn something:
>>>
>>> diff --git a/mm/mlock.c b/mm/mlock.c
>>> index 4e1a6816..7094bac 100644
>>> --- a/mm/mlock.c
>>> +++ b/mm/mlock.c
>>> @@ -469,12 +469,14 @@ static unsigned long __munlock_pagevec_fill(struct pagevec *pvec,
>>> void munlock_vma_pages_range(struct vm_area_struct *vma,
>>> unsigned long start, unsigned long end)
>>> {
>>> + unsigned long orig_start = start;
>>> + unsigned long page_increm = 0;
>>> +
>>> vma->vm_flags &= ~VM_LOCKED;
>>>
>>> while (start < end) {
>>> struct page *page = NULL;
>>> unsigned int page_mask;
>>> - unsigned long page_increm;
>>> struct pagevec pvec;
>>> struct zone *zone;
>>> int zoneid;
>>> @@ -491,6 +493,24 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
>>> &page_mask);
>>>
>>> if (page && !IS_ERR(page)) {
>>> + if (PageTail(page)) {
>>> + struct page *first_page;
>>> + dump_page(page, "Unexpected PageTail");
>>> + printk("start=%lu pfn=%lu orig_start=%lu "
>>> + "page_increm=%lu "
>>> + "vm_start=%lu vm_end=%lu vm_flags=%lu\n",
>>> + start, page_to_pfn(page), orig_start,
>>> + page_increm,
>>> + vma->vm_start, vma->vm_end,
>>> + vma->vm_flags);
>>> + first_page = page->first_page;
>>> + printk("first_page pfn=%lu\n",
>>> + page_to_pfn(first_page));
>>> + dump_page(first_page, "first_page of unexpected PageTail page");
>>> + if (PageCompound(first_page))
>>> + printk("first_page is compound with order=%d\n", compound_order(first_page));
>>> + VM_BUG_ON(true);
>>> + }
>>> if (PageTransHuge(page)) {
>>> lock_page(page);
>>> /*
>>> @@ -525,7 +545,25 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
>>> }
>>> }
>>> /* It's a bug to munlock in the middle of a THP page */
>>> - VM_BUG_ON((start >> PAGE_SHIFT) & page_mask);
>>> + if ((start >> PAGE_SHIFT) & page_mask) {
>>> + dump_page(page, "unexpected middle of THP page");
>>> + printk("start=%lu pfn=%lu orig_start=%lu "
>>
>> In this scenario page might be error or NULL, no?
>>
>
> Hm I doubt page_mask would be nonzero in such case, but who knows what weirdness causes this...
> Feel free to move the dump_page() below printk() so we still get useful info before it crashes on
> dump_page() in such situation.
It happened once, so I moved it, but in the meanwhile I got something useful:
[ 1753.907376] page:ffffea0017130c40 count:0 mapcount:1 mapping: (null) index:0x2
[ 1753.908327] page flags: 0x16fffff80008000(tail)
[ 1753.908973] page dumped because: Unexpected PageTail
[ 1753.909595] start=140340826935296 pfn=6048817 orig_start=140340826935296 page_increm=0 vm_start=140340826935296 vm_end=140340826939392 vm_flags=1210057078
[ 1753.911220] first_page pfn=6048768
[ 1753.911692] page:ffffea0017130000 count:2 mapcount:1 mapping:ffff880612b41f01 index:0x7fa3a5200
[ 1753.912733] page flags: 0x16fffff80384028(uptodate|lru|head|swapbacked|unevictable|mlocked)
[ 1753.913464] page dumped because: first_page of unexpected PageTail page
[ 1753.914387] pc:ffff88062adcc000 pc->flags:2 pc->mem_cgroup:ffff88012b474520
[ 1753.914387] first_page is compound with order=9
[ 1753.914387] ------------[ cut here ]------------
[ 1753.914387] kernel BUG at mm/mlock.c:512!
[ 1753.914387] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 1753.914387] Dumping ftrace buffer:
[ 1753.914387] (ftrace buffer empty)
[ 1753.914387] Modules linked in:
[ 1753.914387] CPU: 26 PID: 36822 Comm: trinity-c337 Tainted: G W 3.14.0-rc6-next-20140317-sasha-00012-ge933921-dirty #226
[ 1753.914387] task: ffff88090cdeb000 ti: ffff88090a868000 task.ti: ffff88090a868000
[ 1753.914387] RIP: 0010:[<ffffffff8129ca7a>] [<ffffffff8129ca7a>] munlock_vma_pages_range+0x12a/0x340
[ 1753.914387] RSP: 0018:ffff88090a869dd8 EFLAGS: 00010292
[ 1753.914387] RAX: 0000000000000023 RBX: ffffea0017130000 RCX: 0000000000000006
[ 1753.914387] RDX: 0000000000000006 RSI: ffff88090cdebcf0 RDI: 0000000000000282
[ 1753.914387] RBP: ffff88090a869ec8 R08: 0000000000000001 R09: 0000000000000001
[ 1753.914387] R10: 0000000000000001 R11: 0000000000000001 R12: 00007fa3a5231000
[ 1753.914387] R13: ffff880613c69400 R14: 0000160000000000 R15: 0000000000000000
[ 1753.914387] FS: 00007fa3a9081700(0000) GS:ffff880b2ba00000(0000) knlGS:0000000000000000
[ 1753.914387] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 1753.914387] CR2: 0000000002fff0a8 CR3: 00000008fa08d000 CR4: 00000000000006a0
[ 1753.914387] Stack:
[ 1753.914387] 00007fa3a5232000 0000000048200176 00007fa3a552a000 ffff880613c6a800
[ 1753.914387] 00007fa3a552a000 00007fa3a5231000 0000000000000000 0000000000000000
[ 1753.914387] 000188090a869e38 0000000000000000 0000000000000000 ffff880613c69400
[ 1753.914387] Call Trace:
[ 1753.914387] [<ffffffff812a0302>] do_munmap+0x1d2/0x360
[ 1753.914387] [<ffffffff844a42e6>] ? down_write+0xa6/0xc0
[ 1753.914387] [<ffffffff812a04d6>] ? vm_munmap+0x46/0x80
[ 1753.914387] [<ffffffff812a04e4>] vm_munmap+0x54/0x80
[ 1753.914387] [<ffffffff812a053c>] SyS_munmap+0x2c/0x40
[ 1753.914387] [<ffffffff844b04d0>] tracesys+0xdd/0xe2
[ 1753.914387] Code: 85 48 89 df e8 98 d0 fc ff 66 f7 03 00 c0 74 1b 48 8b 03 31 f6 f6 c4 40 74 03 8b 73 68 48 c7 c7 58 7d 6e 85 31 c0 e8 52 1f 20 03 <0f> 0b 0f 1f 40 00 eb fe 66 0f 1f 44 00 00 48 8b 03 66 85 c0 79
[ 1753.914387] RIP [<ffffffff8129ca7a>] munlock_vma_pages_range+0x12a/0x340
[ 1753.914387] RSP <ffff88090a869dd8>
Thanks,
Sasha
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