Re: [PATCH 1/2] mm, oom: introduce oom reaper

[Ross Zwisler <zwisler@gmail.com>]

On Thu, Dec 24, 2015 at 2:47 AM, Michal Hocko <mhocko@kernel.org> wrote:
> On Wed 23-12-15 16:00:09, Ross Zwisler wrote:
> [...]
>> While running xfstests on next-20151223 I hit a pair of kernel BUGs
>> that bisected to this commit:
>>
>> 1eb3a80d8239 ("mm, oom: introduce oom reaper")
>
> Thank you for the report and the bisection.
>
>> Here is a BUG produced by generic/029 when run against XFS:
>>
>> [  235.751723] ------------[ cut here ]------------
>> [  235.752194] kernel BUG at mm/filemap.c:208!
>
> This is VM_BUG_ON_PAGE(page_mapped(page), page), right? Could you attach
> the full kernel log? It all smells like a race when OOM reaper tears
> down the mapping and there is a truncate still in progress. But hitting
> the BUG_ON just because of that doesn't make much sense to me. OOM
> reaper is essentially MADV_DONTNEED. I have to think about this some
> more, though, but I am in a holiday mode until early next year so please
> bear with me.

The two stack traces were gathered with next-20151223, so the line numbers
may have moved around a bit when compared to the actual "mm, oom: introduce
oom reaper" commit.

> [...]
>> [  235.765638] Call Trace:
>> [  235.765903]  [<ffffffff811c8493>] delete_from_page_cache+0x63/0xd0
>> [  235.766513]  [<ffffffff811dc3e5>] truncate_inode_page+0xa5/0x120
>> [  235.767088]  [<ffffffff811dc648>] truncate_inode_pages_range+0x1a8/0x7f0
>> [  235.767725]  [<ffffffff81021459>] ? sched_clock+0x9/0x10
>> [  235.768239]  [<ffffffff810db37c>] ? local_clock+0x1c/0x20
>> [  235.768779]  [<ffffffff811feba4>] ? unmap_mapping_range+0x64/0x130
>> [  235.769385]  [<ffffffff811febb4>] ? unmap_mapping_range+0x74/0x130
>> [  235.770010]  [<ffffffff810f5c3f>] ? up_write+0x1f/0x40
>> [  235.770501]  [<ffffffff811febb4>] ? unmap_mapping_range+0x74/0x130
>> [  235.771092]  [<ffffffff811dcd58>] truncate_pagecache+0x48/0x70
>> [  235.771646]  [<ffffffff811dcdb2>] truncate_setsize+0x32/0x40
>> [  235.772276]  [<ffffffff8148e972>] xfs_setattr_size+0x232/0x470
>> [  235.772839]  [<ffffffff8148ec64>] xfs_vn_setattr+0xb4/0xc0
>> [  235.773369]  [<ffffffff8127af87>] notify_change+0x237/0x350
>> [  235.773945]  [<ffffffff81257c87>] do_truncate+0x77/0xc0
>> [  235.774446]  [<ffffffff8125800f>] do_sys_ftruncate.constprop.15+0xef/0x150
>> [  235.775156]  [<ffffffff812580ae>] SyS_ftruncate+0xe/0x10
>> [  235.775650]  [<ffffffff81a527b2>] entry_SYSCALL_64_fastpath+0x12/0x76
>> [  235.776257] Code: 5f 5d c3 48 8b 43 20 48 8d 78 ff a8 01 48 0f 44
>> fb 8b 47 48 85 c0 0f 88 2b 01 00 00 48 c7 c6 a8 57 f0 81 48 89 df e8
>> fa 1a 03 00 <0f> 0b 4c 89 ce 44 89 fa 4c 89 e7 4c 89 45 b0 4c 89 4d b8
>> e8 32
>> [  235.778695] RIP  [<ffffffff811c81f6>] __delete_from_page_cache+0x206/0x440
>> [  235.779350]  RSP <ffff8800bab83b60>
>> [  235.779694] ---[ end trace fac9dd65c4cdd828 ]---
>>
>> And a different BUG produced by generic/095, also with XFS:
>>
>> [  609.398897] ------------[ cut here ]------------
>> [  609.399843] kernel BUG at mm/truncate.c:629!
>
> Hmm, I do not see any BUG_ON at this line. But there is
> BUG_ON(page_mapped(page)) at line 620.

Ditto - check out next-20151223 for real line numbers.

>> [  609.400666] invalid opcode: 0000 [#1] SMP
>> [  609.401512] Modules linked in: nd_pmem nd_btt nd_e820 libnvdimm
>> [  609.402719] CPU: 4 PID: 26782 Comm: fio Tainted: G        W
>
> There was a warning before this triggered. The full kernel log would be
> helpful as well.

Sure, I can gather full kernel logs, but it'll probably after the new year.

> [...]
>> [  609.425325] Call Trace:
>> [  609.425797]  [<ffffffff811dc307>] invalidate_inode_pages2+0x17/0x20
>> [  609.426971]  [<ffffffff81482167>] xfs_file_read_iter+0x297/0x300
>> [  609.428097]  [<ffffffff81259ac9>] __vfs_read+0xc9/0x100
>> [  609.429073]  [<ffffffff8125a319>] vfs_read+0x89/0x130
>> [  609.430010]  [<ffffffff8125b418>] SyS_read+0x58/0xd0
>> [  609.430943]  [<ffffffff81a527b2>] entry_SYSCALL_64_fastpath+0x12/0x76
>> [  609.432139] Code: 85 d8 fe ff ff 01 00 00 00 f6 c4 40 0f 84 59 ff
>> ff ff 49 8b 47 20 48 8d 78 ff a8 01 49 0f 44 ff 8b 47 48 85 c0 0f 88
>> bd 01 00 00 <0f> 0b 4d 3b 67 08 0f 85 70 ff ff ff 49 f7 07 00 18 00 00
>> 74 15
> [...]
>> My test setup is a qemu guest machine with a pair of 4 GiB PMEM
>> ramdisk test devices, one for the xfstest test disk and one for the
>> scratch disk.
>
> Is this just a plain ramdisk device or it needs a special configuration?

Just a plain PMEM ram disk with DAX turned off.  Configuration instructions
for PMEM can be found here:

https://nvdimm.wiki.kernel.org/