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Subject: Re: WARNING: bad unlock balance in xfs_iunlock
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     "Darrick J. Wong" <darrick.wong@oracle.com>,
        Dave Chinner <david@fromorbit.com>,
        syzbot <syzbot+84a67953651a971809ba@syzkaller.appspotmail.com>,
        LKML <linux-kernel@vger.kernel.org>, linux-xfs@vger.kernel.org,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Theodore Ts'o <tytso@mit.edu>,
        syzkaller <syzkaller@googlegroups.com>
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Date:   Tue, 8 May 2018 21:48:54 -0500
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On 5/8/18 2:52 AM, Dmitry Vyukov wrote:
>> Or put another way, how did you arrive at the fs image values in the reproducer,
>> i.e.:
> Currently they are completely random, nobody taught syzkaller about AGFs, etc.

So you just combine a few megabytes of purely random bits out of thin air until
you get something that approximates an xfs filesystem?  Google must have more
computing power than I was aware of.

-Eric

>> oid loop()
>> {
>>   memcpy((void*)0x20000000, "xfs", 4);
>>   memcpy((void*)0x20000100, "./file0", 8);
>>   *(uint64_t*)0x20000200 = 0x20010000;
>>   memcpy((void*)0x20010000,
>>          "\x58\x46\x53\x42\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00"
>>          "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x9f\x98"
>>          "\x99\xff\xcb\xa1\x4e\xe6\xad\x52\x08\x20\x67\x09\xed\x75\x00\x00\x00"
>>          "\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x35\xe0\x00\x00\x00\x00"
>>          "\x00\x00\x35\xe1\x00\x00\x00\x00\x00\x00\x35\xe2\x00\x00\x00\x01\x00"
>>          "\x00\x10\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x03\x55\xb4\xa4"
>>          "\x02\x00\x01\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
>>          "\x00\x0c\x09\x08\x04\x0c\x00\x00\x19\x00\x00\x00\x00\x00\x00\x00\x40"
>>          "\x00\x00\x00\x00\x00\x00\x00\x3d\x00\x00\x00\x00\x00\x00\x0c\xa3\x00"
>>          "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
>>          "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00"
>>          "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x02\x02",
>>          204);
>>
>> ...
>>
>> The in-memory xfs filesystem it constructs is damaged, is that an intentional
>> part of the fuzzing during the test?
> Yes, invalid inputs is part of testing.