Re: [BUG] at include/linux/page-flags.h:415 (PageTransHuge)

From: Thomas Hellstrom
Date: Fri Jan 31 2014 - 10:36:13 EST

On 01/31/2014 04:25 PM, Vlastimil Babka wrote:
> On 01/31/2014 03:58 PM, Thomas Hellstrom wrote:
>> On 01/31/2014 03:40 PM, Vlastimil Babka wrote:
>>> On 01/15/2014 05:06 PM, Daniel Borkmann wrote:
>>>> [keeping netdev in loop as well]
>>>>
>>>> On 01/15/2014 03:27 PM, Vlastimil Babka wrote:
>>>>> On 01/13/2014 12:39 PM, Daniel Borkmann wrote:
>>>>>> On 01/13/2014 11:16 AM, Vlastimil Babka wrote:
>>>>>>> On 01/11/2014 02:32 PM, Daniel Borkmann wrote:
>>>>>>>> On 01/11/2014 07:22 AM, Andrew Morton wrote:
>>>>>>>>> On Fri, 10 Jan 2014 19:23:26 +0100 Daniel Borkmann
>>>>>>>>> <borkmann@xxxxxxxxxxxxx> wrote:
>>>>>>>>>
>>>>>>>>>> This is being reliably triggered for each mmaped() packet(7)
>>>>>>>>>> socket from user space, basically during unmapping resp.
>>>>>>>>>> closing the TX socket.
>>>>>>>>>>
>>>>>>>>>> I believe due to some change in transparent hugepages code ?
>>>>>>>>>>
>>>>>>>>>> When I disable transparent hugepages, everything works fine,
>>>>>>>>>> no BUG triggered.
>>>>>>>>>>
>>>>>>>>>> I'd be happy to test patches.
>>>>>>>>> Did the inclusion of c424be1cbbf852e46acc8 ("mm: munlock: fix
>>>>>>>>> a bug
>>>>>>>>> where THP tail page is encountered") in current mainline fix
>>>>>>>>> this?
>>>>>>>> Thanks for your answer Andrew!
>>>>>>>>
>>>>>>>> Hm, I just cherry-picked that onto current net-next as I have
>>>>>>>> some work
>>>>>>>> there, and this time I got ...
>>>>>>>>
>>>>>>>> (User space uses packet mmap() and mlockall(MCL_CURRENT |
>>>>>>>> MCL_FUTURE)
>>>>>>>> and on shutdown munlockall() ...)
>>>>>>>>
>>>>>>>> [ 63.863672] ------------[ cut here ]------------
>>>>>>>> [ 63.863702] kernel BUG at mm/mlock.c:507!
>>>>>>>> [ 63.863721] invalid opcode: 0000 [#1] SMP
>>>>>>>> [ 63.863743] Modules linked in: fuse ebtable_nat xt_CHECKSUM
>>>>>>>> nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE
>>>>>>>> ip6table_nat nf_nat_ipv6 ip6table_mangle ip6t_REJECT
>>>>>>>> nf_conntrack_ipv6 nf_defrag_ipv6 iptable_nat nf_nat_ipv4 nf_nat
>>>>>>>> iptable_mangle nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack
>>>>>>>> nf_conntrack bridge ebtable_filter ebtables stp llc
>>>>>>>> ip6table_filter ip6_tables rfcomm bnep snd_hda_codec_hdmi
>>>>>>>> snd_hda_codec_realtek snd_hda_intel snd_hda_codec iwlwifi
>>>>>>>> cfg80211 snd_hwdep btusb snd_seq bluetooth sdhci_pci
>>>>>>>> snd_seq_device e1000e tpm_tis snd_pcm thinkpad_acpi sdhci ptp
>>>>>>>> tpm uvcvideo pps_core snd_page_alloc snd_timer snd rfkill
>>>>>>>> mmc_core iTCO_wdt iTCO_vendor_support lpc_ich mfd_core
>>>>>>>> soundcore joydev wmi videobuf2_vmalloc videobuf2_memops
>>>>>>>> videobuf2_core i2c_i801 pcspkr videodev media uinput i915
>>>>>>>> [ 63.864152] i2c_algo_bit drm_kms_helper drm i2c_core video
>>>>>>>> [ 63.864181] CPU: 1 PID: 1617 Comm: trafgen Not tainted
>>>>>>>> 3.13.0-rc6+ #15
>>>>>>>> [ 63.864209] Hardware name: LENOVO 2429BP3/2429BP3, BIOS
>>>>>>>> G4ET37WW (1.12 ) 05/29/2012
>>>>>>>> [ 63.864242] task: ffff8801ee060000 ti: ffff8800b5954000
>>>>>>>> task.ti: ffff8800b5954000
>>>>>>>> [ 63.864274] RIP: 0010:[<ffffffff8116fa9a>]
>>>>>>>> [<ffffffff8116fa9a>] munlock_vma_pages_range+0x2ea/0x2f0
>>>>>>>> [ 63.864318] RSP: 0018:ffff8800b5955e08 EFLAGS: 00010202
>>>>>>>> [ 63.864341] RAX: 00000000000001ff RBX: ffff8800b58f7508 RCX:
>>>>>>>> 0000000000000034
>>>>>>>> [ 63.864372] RDX: 00000007f0708992 RSI: ffffea0002c3e700 RDI:
>>>>>>>> ffffea0002c3e700
>>>>>>>> [ 63.864402] RBP: ffff8800b5955ee0 R08: 3800000000000000 R09:
>>>>>>>> a8000b0f9c000000
>>>>>>>> [ 63.864432] R10: 57ffdef066c3e700 R11: ffffff5cfb00c14a R12:
>>>>>>>> ffffea0002c3e700
>>>>>>>> [ 63.864462] R13: ffff8800b5955f48 R14: 00007f0708992000 R15:
>>>>>>>> 00007f0708992000
>>>>>>>> [ 63.864492] FS: 00007f0708b92740(0000)
>>>>>>>> GS:ffff88021e240000(0000) knlGS:0000000000000000
>>>>>>>> [ 63.864526] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>>>>> [ 63.864551] CR2: 00007f33bb373000 CR3: 00000000b2a2c000 CR4:
>>>>>>>> 00000000001407e0
>>>>>>>> [ 63.864581] Stack:
>>>>>>>> [ 63.864593] ffff8800b5955ed0 00007f0708b91fff
>>>>>>>> 00007f0708b92000 ffff8800b5955e48
>>>>>>>> [ 63.864632] 000001ff810c864b ffff8801ee060000
>>>>>>>> 0000000000000000 0000000000000000
>>>>>>>> [ 63.864669] ffff8800b5955e58 ffff8801ee060000
>>>>>>>> 0000000700000086 ffff8801ee060000
>>>>>>>> [ 63.864708] Call Trace:
>>>>>>>> [ 63.864724] [<ffffffff816956bc>] ?
>>>>>>>> _raw_spin_unlock_irq+0x2c/0x30
>>>>>>>> [ 63.864754] [<ffffffff81171b52>] ? vma_merge+0xc2/0x330
>>>>>>>> [ 63.864786] [<ffffffff8116fb9c>] mlock_fixup+0xfc/0x190
>>>>>>>> [ 63.864812] [<ffffffff8116fde7>] do_mlockall+0x87/0xc0
>>>>>>>> [ 63.864836] [<ffffffff811702df>] sys_munlockall+0x2f/0x50
>>>>>>>> [ 63.864873] [<ffffffff8169e192>]
>>>>>>>> system_call_fastpath+0x16/0x1b
>>>>>>>> [ 63.864898] Code: d7 48 89 95 28 ff ff ff e8 a4 04 fe ff 84
>>>>>>>> c0 48 8b 95 28 ff ff ff 0f 85 5a ff ff ff e9 46 ff ff ff e8 3f
>>>>>>>> ac 51 00 e8 34 ac 51 00 <0f> 0b 0f 1f 40 00 0f 1f 44 00 00 55
>>>>>>>> 48 89 e5 41 57 41 56 41 55
>>>>>>>> [ 63.865114] RIP [<ffffffff8116fa9a>]
>>>>>>>> munlock_vma_pages_range+0x2ea/0x2f0
>>>>>>>> [ 63.865148] RSP <ffff8800b5955e08>
>>>>>>>> [ 63.874968] ------------[ cut here ]------------
>>>>>>>>
>>>>>>>> ... when I find some time, I'll try with normal torvalds' tree,
>>>>>>>> maybe some
>>>>>>>> other patches are missing as well, not sure right now.
>>>>>>> Uh so the triggered assertion is the one added by this very
>>>>>>> patch, and there are no more changes wrt this in mainline.
>>>>>>>
>>>>>>> If you can still try debug patches, please try this. Thanks.
>>>>>> Yes, thanks, I'll come back to you some time by today.
>>>>> Daniel sent me (off-list) instructions to reproduce:
>>>>>
>>>>>> Then in the kernel source tree, you'll find:
>>>>>>
>>>>>> tools/testing/selftests/net/
>>>>>>
>>>>>> There, just do a 'make' and run ./psock_tpacket
>>>>> It reproduces deterministically in mainline since 3.12, i.e. my
>>>>> munlock
>>>>> performance series. Based on the initial debug output, I've
>>>>> expanded the
>>>>> debug patch below a bit:
>>>>>
>>>>>>> From: Vlastimil Babka <vbabka@xxxxxxx>
>>>>>>> Date: Mon, 13 Jan 2014 11:13:53 +0100
>>>>>>> Subject: [PATCH] debug munlock_vma_pages_range
>>>>>>>
>>>>>>> ---
>>>>>>> mm/mlock.c | 22 ++++++++++++++++++++--
>>>>>>> 1 file changed, 20 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/mm/mlock.c b/mm/mlock.c
>>>>>>> index c59c420..7d0e29a 100644
>>>>>>> --- a/mm/mlock.c
>>>>>>> +++ b/mm/mlock.c
>>>>>>> @@ -448,12 +448,14 @@ 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;
>>>>>>> @@ -504,7 +506,23 @@ 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);
>>>>>>> + printk("start=%lu pfn=%lu orig_start=%lu "
>>>>>>> + "prev_page_increm=%lu page_mask=%u "
>>>>>>> + "vm_start=%lu vm_end=%lu vm_flags=%lu\n",
>>>>>>> + start, page_to_pfn(page), orig_start,
>>>>>>> + page_increm, page_mask,
>>>>>>> + vma->vm_start, vma->vm_end,
>>>>>>> + vma->vm_flags);
>>>>> + printk("vm_ops=%pF, open=%pF, fault=%pF,
>>>>> remap_pages=%pF\n", vma->vm_ops,
>>>>> + vma->vm_ops->open,
>>>>> vma->vm_ops->fault, vma->vm_ops->remap_pages);
>>>>> + if (PageCompound(page)) {
>>>>> + printk("page is compound with
>>>>> order=%d\n", compound_order(page));
>>>>> + }
>>>>>>> + if (PageTail(page)) {
>>>>>>> + struct page *first_page = page->first_page;
>>>>>>> + printk("first_page pfn=%lu\n",
>>>>>>> + page_to_pfn(first_page));
>>>>>>> + dump_page(first_page);
>>>>>>> + }
>>>>>>> + VM_BUG_ON(true);
>>>>>>> + }
>>>>>>> page_increm = 1 + page_mask;
>>>>>>> start += page_increm * PAGE_SIZE;
>>>>>>> next:
>>>>>>>
>>>>> And got output like this:
>>>>>
>>>>> page:ffffea0002474a40 count:5 mapcount:1 mapping: (null)
>>>>> index:0x0
>>>>> page flags: 0x100000000004004(referenced|head)
>>>>> start=140242647736320 pfn=682616 orig_start=140242647736320
>>>>> prev_page_increm=0 page_mask=511 vm_start=140242647736320
>>>>> vm_end=140242651930624 vm_flags=268435707
>>>>> vm_ops=packet_mmap_ops+0x0/0xfffffffffffff8e0 [af_packet],
>>>>> open=packet_mm_open+0x0/0x30 [af_packet], fault= (null),
>>>>> remap_pages= (null)
>>>>> page is compound with order=2
>>>>>
>>>>> Observations:
>>>>> - address 140242647736320 is where the vma starts, and is not
>>>>> aligned to 512 pages
>>>>> (so it cannot be a THP head which the munlock expects). Yet
>>>>> there is a head page
>>>>> that triggers the PageTransHuge() and consequently
>>>>> hpage_nr_pages() in munlock_vma_page()
>>>>> That's why page_mask is determined to be 511 and the code
>>>>> thinks it's in the
>>>>> middle of a THP page.
>>>>> - in fact, the page is a compound page with order=2
>>>>> - the VM flags (except (may)read/write) are VM_SHARED and VM_MIXEDMAP
>>>>> - the vma was mmapped by packet_mmap() (net/packet/af_packet.c)
>>>>> which uses
>>>>> vm_insert_page(), which adds the VM_MIXEDMAP flag
>>>>> - the buffers that are mapped were allocated by
>>>>> alloc_one_pg_vec_page()
>>>>> where flags indeed include __GFP_COMP
>>>>>
>>>>> So clearly there is a way to have mlock/munlock operate on a vma
>>>>> that contains
>>>>> compound pages and confuse the checks for PageTransHuge().
>>>>>
>>>>> The checks for THP in munlock came with commit ff6a6da60b89 ("mm:
>>>>> accelerate munlock()
>>>>> treatment of THP pages"), i.e. since 3.9, but did not trigger a
>>>>> bug. It however
>>>>> makes munlock_vma_pages_range() skip pages until the next
>>>>> 512-pages-aligned page,
>>>>> when it encounters a head page. If the head page is of smaller
>>>>> order and is followed
>>>>> by normal LRU pages (theoretically, I'm not sure if that's
>>>>> possible, or done anywhere),
>>>>> they wouldn't get munlocked.
>>>>>
>>>>> My commit 7225522bb429 ("mm: munlock: batch non-THP page isolation
>>>>> and
>>>>> munlock+putback using pagevec") (since 3.12) has added a new
>>>>> PageTransHuge() check
>>>>> that can trigger on tail pages of the compound page here. Commit
>>>>> c424be1cbbf852e46acc8
>>>>> ("mm: munlock: fix a bug where THP tail page is encountered") in
>>>>> current rc's removes
>>>>> one class of bugs here, but still non-THP compound pages are not
>>>>> expected in mlock/munlock,
>>>>> which leads to this assertion failing.
>>>>>
>>>>> The question is what is the correct fix, and I'm not that familiar
>>>>> with VM_MIXEDMAP
>>>>> to decide.
>>>>>
>>>>> Option 1: mlocking VM_MIXEDMAP vma's has no sense. They should be
>>>>> treated like VM_PFNMAP
>>>>> and added to VM_SPECIAL, which makes m(un)lock skip
>>>>> them completely.
>>>>>
>>>>> Option 2: if indeed VM_MIXEDMAP can contain PageLRU pages for
>>>>> which mlocking is useful,
>>>>> VM_NO_THP should be checked in munlock before
>>>>> attempting PageTransHuge() and
>>>>> friends. VM_NO_THP already contains VM_MIXEDMAP, so
>>>>> knowing that there can be
>>>>> no THP means we don't try optimize for it and no
>>>>> unexpected head pages trip us.
>>>>>
>>>>> Thoughts?
>>> OK, here's a RFC patch to hopefully help get us somewhere. I went for
>>> Option1, as I didn't see anyone using VM_MIXEDMAP also for LRU pages,
>>> and Option2 was ugly to implement and also seemed quite arbitrary. I'm
>>> not sure if making VM_MIXEDMAP also non-mergeable this way is an issue
>>> though.
>>>
>>>
>>
>> Hi!
>>
>> Forgive an ignorant question, but are anonymous COW'd pages LRU pages?
>
> I believe so, but I've checked where VM_MIXEDMAP is used in TTM and it
> seems all those vma's are also VM_IO which means they are already
> included in VM_SPECIAL and this change won't affect them.
>
> Vlastimil
>

OK. Thanks.

/Thomas




>> The reason I'm asking is that TTM VM_MIXEDMAP vmas may contain such
>> pages.
>>
>> /Thomas
>>
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