Re: [3.15rc1] BUG at mm/filemap.c:202!

[Richard Weinberger <richard.weinberger@gmail.com>]

On Wed, Apr 16, 2014 at 10:40 PM, Hugh Dickins <hughd@google.com> wrote:
> On Tue, 15 Apr 2014, Dave Jones wrote:
>
>> kernel BUG at mm/filemap.c:202!
>> invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
>> Modules linked in: tun fuse bnep rfcomm nfnetlink llc2 af_key ipt_ULOG can_raw can_bcm scsi_transport_iscsi nfc caif_socket caif af_802154 ieee802154 phonet af_r
>> xrpc can pppoe pppox ppp_generic slhc irda crc_ccitt rds rose x25 atm netrom appletalk ipx p8023 psnap p8022 llc ax25 cfg80211 coretemp hwmon x86_pkg_temp_thermal kvm_intel kvm
>>  xfs libcrc32c snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic crct10dif_pclmul crc32c_intel ghash_clmulni_intel snd_hda_intel snd_hda_controller snd_hda_codec e
>> 1000e btusb bluetooth microcode pcspkr serio_raw snd_hwdep snd_seq snd_seq_device snd_pcm 6lowpan_iphc usb_debug rfkill ptp pps_core shpchp snd_timer snd soundcore
>> CPU: 3 PID: 14244 Comm: trinity-main Not tainted 3.15.0-rc1+ #188
>> task: ffff8801be2c50a0 ti: ffff8801d6830000 task.ti: ffff8801d6830000
>> RIP: 0010:[<ffffffff9915b4d5>]  [<ffffffff9915b4d5>] __delete_from_page_cache+0x315/0x320
>> RSP: 0018:ffff8801d6831b10  EFLAGS: 00010046
>> RAX: 0000000000000000 RBX: 0000000000000003 RCX: 000000000000001d
>> RDX: 000000000000012a RSI: ffffffff99a9a1c0 RDI: ffffffff99a6dad5
>> RBP: ffff8801d6831b60 R08: 000000000000005d R09: ffff8801b0361530
>> R10: ffff8801d6831b28 R11: 0000000000000000 R12: ffffea000734d440
>> R13: ffff880241235008 R14: 0000000000000000 R15: ffff880241235010
>> FS:  00007f81925cf740(0000) GS:ffff880244600000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 0000000000630058 CR3: 0000000019c0e000 CR4: 00000000001407e0
>> DR0: 0000000000df3000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
>> Stack:
>>  ffff880241235020 ffff880241235038 ffff8801b0361530 ffff8801b0361640
>>  000000001da16adc ffffea000734d440 ffff880241235020 0000000000000000
>>  0000000000000000 000000000000005d ffff8801d6831b88 ffffffff9915b51d
>> Call Trace:
>>  [<ffffffff9915b51d>] delete_from_page_cache+0x3d/0x70
>>  [<ffffffff9916ab7b>] truncate_inode_page+0x5b/0x90
>>  [<ffffffff991759ab>] shmem_undo_range+0x30b/0x780
>>  [<ffffffff990a99e5>] ? local_clock+0x25/0x30
>>  [<ffffffff99175e34>] shmem_truncate_range+0x14/0x30
>>  [<ffffffff99175f1d>] shmem_evict_inode+0xcd/0x150
>>  [<ffffffff991e46e7>] evict+0xa7/0x170
>>  [<ffffffff991e5005>] iput+0xf5/0x180
>>  [<ffffffff991df390>] dentry_kill+0x210/0x250
>>  [<ffffffff991df43c>] dput+0x6c/0x110
>>  [<ffffffff991c8c19>] __fput+0x189/0x200
>>  [<ffffffff991c8cde>] ____fput+0xe/0x10
>>  [<ffffffff990900b4>] task_work_run+0xb4/0xe0
>>  [<ffffffff9906ea92>] do_exit+0x302/0xb80
>>  [<ffffffff99349843>] ? __this_cpu_preempt_check+0x13/0x20
>>  [<ffffffff9907038c>] do_group_exit+0x4c/0xc0
>>  [<ffffffff99070414>] SyS_exit_group+0x14/0x20
>>  [<ffffffff9975a964>] tracesys+0xdd/0xe2
>> Code: 4c 89 30 e9 80 fe ff ff 48 8b 75 c0 4c 89 ff e8 e2 8e 1c 00 84 c0 0f 85 6c fe ff ff e9 4f fe ff ff 0f 1f 44 00 00 e8 4e 85 5e 00 <0f> 0b e8 84 1d f1 ff 0f :
>>
>>
>>  202         BUG_ON(page_mapped(page));
>
> I've been wrestling with this report, but made no progress;
> maybe if I set down a few thoughts, someone can help us forward.
>
> It is reasonable to assume (but unreasonable to hold on too tightly
> to the assumption) that this is related to Dave's contemporaneous
> report of BUG: Bad rss-counter state mm:ffff88023fc73c00 idx:0 val:5
>
> I don't know if they both occurred in the same session; but whether
> or not they did, the BUG_ON(page_mapped(page)) from inode eviction
> implies that not every pte mapping a shmem file page had been located
> when its last mapper exited; and the rss-counter message implies that
> there were five pte mappings of file(s) which could not be located
> when their mapper exited.
>
> It is also reasonable to assume (but unreasonable to hold on too
> tightly to the assumption) that this is another manifestation of
> the same unsolved mm/filemap.c:202 that Sasha reported on rc5-next
> a month ago, https://lkml.org/lkml/2014/3/7/298
>
> Now that one occurred, not while evicting a shmem inode, but while
> punching a hole in it with madvise(,,MADV_REMOVE).  At the time I
> set it aside to consider when improving shmem_fallocate(), but now
> it looks more like a precursor of Dave's.
>
> One way this could happen is if we have racing tasks setting up
> ptes without the necessary locking, one placing its pte on top of
> another's, so page_mapcount goes up by 2 but comes down by 1 later.
> But I failed to find anywhere in the code in danger of doing that.
>
> Another way it could happen is if a vma is removed from i_mmap tree
> and i_mmap_nonlinear list, without zap_pte_range() having zapped all
> of its ptes; but I don't see where that could happen either.
>
> Sasha's came before shmem participated in Kirill's filemap_map_pages
> fault-around; but his pte_same/pte_none checking under ptl there looks
> correct anyway.  I've not found any recent change likely to blame.
>
> Help!

Using a trinity as of today I'm able to trigger this bug on UML within seconds.
If you want me to test patch, I can help.

I'm also observing one strange fact, I can trigger this on any kernel version.
So far I've managed UML to crash on 3.0 to 3.15-rc...

-- 
Thanks,
//richard

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