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Subject: Re: kernel BUG at fs/inode.c:LINE!
To: Dmitry Vyukov <dvyukov@google.com>,
        Al Viro <viro@zeniv.linux.org.uk>
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From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
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Date: Tue, 18 Dec 2018 19:40:50 +0900
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On 2018/12/17 19:08, Dmitry Vyukov wrote:
> On Mon, Dec 17, 2018 at 8:21 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
>>>  slab_pre_alloc_hook mm/slab.h:423 [inline]
>>>  slab_alloc mm/slab.c:3365 [inline]
>>>  kmem_cache_alloc+0x2c4/0x730 mm/slab.c:3539
>>>  __d_alloc+0xc8/0xb90 fs/dcache.c:1599
>>> ------------[ cut here ]------------
>>> kernel BUG at fs/inode.c:1566!
>>>  d_alloc_anon fs/dcache.c:1698 [inline]
>>>  d_make_root+0x43/0xc0 fs/dcache.c:1885
>>>  autofs_fill_super+0x6f1/0x1c30 fs/autofs/inode.c:273
>>
>> Huh?  BUG is in iput(), AFAICS, so the stack trace is rather misreported.
> 
> Yes, it's a known problem that kernel is generally incapable of
> producing parsable crash reports. I think Tetsuo is working on a
> solution, but it takes very large amount of discussions and months of
> time.

The solution, CONFIG_PRINTK_FROM option (which will be renamed to CONFIG_PRINTK_CALLER
option tomorrow), just arrived at linux-next-20181218. We can try it...

But currently syzbot cannot boot using linux-next-20181218 due to
"Kernel panic - not syncing: Can't create rootfs" presumably due to changes merged by
"Merge branches 'work.mount', 'work.misc', 'misc.misc' and 'work.iov_iter' into for-next".
I think that we need to examine this "Can't create rootfs" problem, for
the merge window is approaching...