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

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

[Daniel Borkmann]

[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@iogearbox.net> 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@suse.cz>
>>> 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?

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

[Vlastimil Babka]

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@iogearbox.net> 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@suse.cz>
>>>> 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.

Actually a nice third option would be that the vma in question would
include also another flag (other than VM_MIXEDMAP) that would declare it
can contain compound pages. But I didn't find any such rule documented,
perhaps VM_IO would be a candidate?

I added people that touched VM_MIXEDMAP in the past to CC.


-------8<-------
From: Vlastimil Babka <vbabka@suse.cz>
Date: Fri, 31 Jan 2014 11:50:21 +0100
Subject: [PATCH] mm: include VM_MIXEDMAP flag in the VM_SPECIAL list to avoid
 m(un)locking

Daniel Borkmann reported a bug with VM_BUG_ON assertions failing where
munlock_vma_pages_range() thinks it's unexpectedly in the middle of a THP page.
This can be reproduced in tools/testing/selftests/net/ by running make and
then ./psock_tpacket.

The problem is that an order=2 compound page (allocated by
alloc_one_pg_vec_page() is part of the munlocked VM_MIXEDMAP vma (mapped by
packet_mmap()) and mistaken for a THP page and assumed to be order=9.

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 just makes munlock_vma_pages_range() skip such compound pages until the next
512-pages-aligned page, when it encounters a head page. This is however not a
problem for vma's where mlocking has no effect anyway, but it can distort the
accounting.
Since commit 7225522bb ("mm: munlock: batch non-THP page isolation and
munlock+putback using pagevec") this can trigger a VM_BUG_ON in PageTransHuge()
check.

This patch fixes the issue by adding VM_MIXEDMAP flag to VM_SPECIAL - a list of
flags that make vma's non-mlockable and non-mergeable. The reasoning is that
VM_MIXEDMAP vma's are similar to VM_PFNMAP, which is already on the VM_SPECIAL
list, and both are intended for non-LRU pages where mlocking makes no sense
anyway.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Daniel Borkmann <borkmann@iogearbox.net>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: John David Anglin <dave.anglin@bell.net>
Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Carsten Otte <cotte@de.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jared Hulbert <jaredeh@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 include/linux/mm.h | 2 +-
 mm/huge_memory.c   | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f28f46e..f9b04ac 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -175,7 +175,7 @@ extern unsigned int kobjsize(const void *objp);
  * Special vmas that are non-mergable, non-mlock()able.
  * Note: mm/huge_memory.c VM_NO_THP depends on this definition.
  */
-#define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_PFNMAP)
+#define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_PFNMAP | VM_MIXEDMAP)
 
 /*
  * mapping from the currently active vm_flags protection bits (the
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 82166bf..f32fffb 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1963,7 +1963,7 @@ out:
 	return ret;
 }
 
-#define VM_NO_THP (VM_SPECIAL|VM_MIXEDMAP|VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
+#define VM_NO_THP (VM_SPECIAL|VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
 
 int hugepage_madvise(struct vm_area_struct *vma,
 		     unsigned long *vm_flags, int advice)
-- 
1.8.4.5


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

[Thomas Hellstrom]

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@iogearbox.net> 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 videode
 v 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@suse.cz>
>>>>> 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?
The reason I'm asking is that TTM VM_MIXEDMAP vmas may contain such pages.

/Thomas

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

[Vlastimil Babka]

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@iogearbox.net> 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 videod
 ev 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@suse.cz>
>>>>>> 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

> The reason I'm asking is that TTM VM_MIXEDMAP vmas may contain such pages.
>
> /Thomas
>
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Re: [BUG] at include/linux/page-flags.h:415 (PageTransHuge)

[Thomas Hellstrom]

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@iogearbox.net> 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@suse.cz>
>>>>>>> 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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Re: [BUG] at include/linux/page-flags.h:415 (PageTransHuge)

[Hannes Frederic Sowa]

Hi!

On Fri, Jan 31, 2014 at 03:40:38PM +0100, Vlastimil Babka wrote:
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Fri, 31 Jan 2014 11:50:21 +0100
> Subject: [PATCH] mm: include VM_MIXEDMAP flag in the VM_SPECIAL list to avoid
>  m(un)locking
> 
> Daniel Borkmann reported a bug with VM_BUG_ON assertions failing where
> munlock_vma_pages_range() thinks it's unexpectedly in the middle of a THP page.
> This can be reproduced in tools/testing/selftests/net/ by running make and
> then ./psock_tpacket.
> 
> The problem is that an order=2 compound page (allocated by
> alloc_one_pg_vec_page() is part of the munlocked VM_MIXEDMAP vma (mapped by
> packet_mmap()) and mistaken for a THP page and assumed to be order=9.
> 
> 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 just makes munlock_vma_pages_range() skip such compound pages until the next
> 512-pages-aligned page, when it encounters a head page. This is however not a
> problem for vma's where mlocking has no effect anyway, but it can distort the
> accounting.
> Since commit 7225522bb ("mm: munlock: batch non-THP page isolation and
> munlock+putback using pagevec") this can trigger a VM_BUG_ON in PageTransHuge()
> check.
> 
> This patch fixes the issue by adding VM_MIXEDMAP flag to VM_SPECIAL - a list of
> flags that make vma's non-mlockable and non-mergeable. The reasoning is that
> VM_MIXEDMAP vma's are similar to VM_PFNMAP, which is already on the VM_SPECIAL
> list, and both are intended for non-LRU pages where mlocking makes no sense
> anyway.

I also ran into this problem and wanted to ask what the status of this
patch is? Does it need further testing? I can surely help with that. ;)

Thanks,

  Hannes

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

[Daniel Borkmann]

Hi Vlastimil,

On 02/07/2014 07:58 PM, Hannes Frederic Sowa wrote:
> On Fri, Jan 31, 2014 at 03:40:38PM +0100, Vlastimil Babka wrote:
>> From: Vlastimil Babka <vbabka@suse.cz>
>> Date: Fri, 31 Jan 2014 11:50:21 +0100
>> Subject: [PATCH] mm: include VM_MIXEDMAP flag in the VM_SPECIAL list to avoid
>>   m(un)locking
>>
>> Daniel Borkmann reported a bug with VM_BUG_ON assertions failing where
>> munlock_vma_pages_range() thinks it's unexpectedly in the middle of a THP page.
>> This can be reproduced in tools/testing/selftests/net/ by running make and
>> then ./psock_tpacket.
>>
>> The problem is that an order=2 compound page (allocated by
>> alloc_one_pg_vec_page() is part of the munlocked VM_MIXEDMAP vma (mapped by
>> packet_mmap()) and mistaken for a THP page and assumed to be order=9.
>>
>> 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 just makes munlock_vma_pages_range() skip such compound pages until the next
>> 512-pages-aligned page, when it encounters a head page. This is however not a
>> problem for vma's where mlocking has no effect anyway, but it can distort the
>> accounting.
>> Since commit 7225522bb ("mm: munlock: batch non-THP page isolation and
>> munlock+putback using pagevec") this can trigger a VM_BUG_ON in PageTransHuge()
>> check.
>>
>> This patch fixes the issue by adding VM_MIXEDMAP flag to VM_SPECIAL - a list of
>> flags that make vma's non-mlockable and non-mergeable. The reasoning is that
>> VM_MIXEDMAP vma's are similar to VM_PFNMAP, which is already on the VM_SPECIAL
>> list, and both are intended for non-LRU pages where mlocking makes no sense
>> anyway.

Thanks a lot for your efforts.

Is your patch queued up somewhere for mainline and stable?

> I also ran into this problem and wanted to ask what the status of this
> patch is? Does it need further testing? I can surely help with that. ;)
>
> Thanks,
>
>    Hannes
>

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