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Re: fs, net: deadlock between bind/splice on af_unix

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On Wed, Jan 18, 2017 at 1:17 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Tue, Jan 17, 2017 at 10:21 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>> On Mon, Jan 16, 2017 at 1:32 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
>>> On Fri, Dec 9, 2016 at 7:41 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>>>> On Thu, Dec 08, 2016 at 10:32:00PM -0800, Cong Wang wrote:
>>>>
>>>>> > Why do we do autobind there, anyway, and why is it conditional on
>>>>> > SOCK_PASSCRED?  Note that e.g. for SOCK_STREAM we can bloody well get
>>>>> > to sending stuff without autobind ever done - just use socketpair()
>>>>> > to create that sucker and we won't be going through the connect()
>>>>> > at all.
>>>>>
>>>>> In the case Dmitry reported, unix_dgram_sendmsg() calls unix_autobind(),
>>>>> not SOCK_STREAM.
>>>>
>>>> Yes, I've noticed.  What I'm asking is what in there needs autobind triggered
>>>> on sendmsg and why doesn't the same need affect the SOCK_STREAM case?
>>>>
>>>>> I guess some lock, perhaps the u->bindlock could be dropped before
>>>>> acquiring the next one (sb_writer), but I need to double check.
>>>>
>>>> Bad idea, IMO - do you *want* autobind being able to come through while
>>>> bind(2) is busy with mknod?
>>>
>>>
>>> Ping. This is still happening on HEAD.
>>>
>>
>> Thanks for your reminder. Mind to give the attached patch (compile only)
>> a try? I take another approach to fix this deadlock, which moves the
>> unix_mknod() out of unix->bindlock. Not sure if there is any unexpected
>> impact with this way.
>
>
> I instantly hit:
>

Oh, sorry about it, I forgot to initialize struct path...

Attached is the updated version, I just did a boot test, no crash at least. ;)

Thanks!

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Re: fs, net: deadlock between bind/splice on af_unix Cong Wang <xiyou.wangcong@gmail.com> - 2017-01-17 22:30 +0100
  Re: fs, net: deadlock between bind/splice on af_unix Dmitry Vyukov <dvyukov@google.com> - 2017-01-18 10:30 +0100
    Re: fs, net: deadlock between bind/splice on af_unix Cong Wang <xiyou.wangcong@gmail.com> - 2017-01-20 06:00 +0100
      Re: fs, net: deadlock between bind/splice on af_unix Dmitry Vyukov <dvyukov@google.com> - 2017-01-21 00:00 +0100
        Re: fs, net: deadlock between bind/splice on af_unix Cong Wang <xiyou.wangcong@gmail.com> - 2017-01-23 20:10 +0100
  Re: fs, net: deadlock between bind/splice on af_unix Mateusz Guzik <mguzik@redhat.com> - 2017-01-27 00:40 +0100
    Re: fs, net: deadlock between bind/splice on af_unix Cong Wang <xiyou.wangcong@gmail.com> - 2017-01-27 06:20 +0100
      Re: fs, net: deadlock between bind/splice on af_unix Mateusz Guzik <mguzik@redhat.com> - 2017-01-27 07:50 +0100

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