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

From	Cong Wang <xiyou.wangcong@gmail.com>
Newsgroups	linux.kernel
Subject	Re: fs, net: deadlock between bind/splice on af_unix
Date	2017-01-17 22:30 +0100
Message-ID	<t0Juh-3NG-3@gated-at.bofh.it> (permalink)
References	(2 earlier) <sMgVc-4sj-17@gated-at.bofh.it> <sMiki-5ep-11@gated-at.bofh.it> <sMn0B-8kb-1@gated-at.bofh.it> <sMnai-8nx-13@gated-at.bofh.it> <t0bVE-6TE-13@gated-at.bofh.it>
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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.

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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