From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To: Jiacheng Xu <578001344xu@gmail.com>
Cc: netdev@vger.kernel.org, linux-bluetooth@vger.kernel.org,
Jakub Kicinski <kuba@kernel.org>,
"open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>,
Eric Dumazet <edumazet@google.com>,
linux-kernel@vger.kernel.org, marcel@holtmann.org,
johan.hedberg@gmail.com, David Miller <davem@davemloft.net>,
luiz.dentz@gmail.com, Paolo Abeni <pabeni@redhat.com>
Subject: Re: possible deadlock in rfcomm_sk_state_change
Date: Mon, 29 Aug 2022 23:48:01 -0700 [thread overview]
Message-ID: <f53dfd70-f8b3-8401-3f5a-d738b2f242e1@gmail.com> (raw)
In-Reply-To: <CAO4S-mfTNEKCs8ZQcT09wDzxX8MfidmbTVzaFMD3oG4i7Ytynw@mail.gmail.com>
+cc Bluetooth and Networking maintainers
Hi Jiacheng,
On 28/8/22 04:03, Jiacheng Xu wrote:
> Hi,
>
> I believe the deadlock is more than possible but actually real.
> I got a poc that could stably trigger the deadlock.
>
> poc: https://drive.google.com/file/d/1PjqvMtHsrrGM1MIRGKl_zJGR-teAMMQy/view?usp=sharing
>
> Description/Root cause:
> In rfcomm_sock_shutdown(), lock_sock() is called when releasing and
> shutting down socket.
> However, lock_sock() has to be called once more when the sk_state is
> changed because the
> lock is not always held when rfcomm_sk_state_change() is called. One
> such call stack is:
>
> rfcomm_sock_shutdown():
> lock_sock();
> __rfcomm_sock_close():
> rfcomm_dlc_close():
> __rfcomm_dlc_close():
> rfcomm_dlc_lock();
> rfcomm_sk_state_change():
> lock_sock();
>
> Besides the recursive deadlock, there is also an
> issue of a lock hierarchy inversion between rfcomm_dlc_lock() and
> lock_sock() if the socket is locked in rfcomm_sk_state_change().
Thanks for the poc and for following the trail all the way to the root
cause - this was a known issue and I didn't realize the patch wasn't
applied.
> > Reference:
https://lore.kernel.org/all/20211004180734.434511-1-desmondcheongzx@gmail.com/
>
Fwiw, I tested the patch again with syzbot. It still applies cleanly to
the head of bluetooth-next and seems to address the root cause.
Any thoughts from the maintainers on this issue and the proposed fix?
Best,
Desmond
next prev parent reply other threads:[~2022-08-30 6:48 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-27 16:19 possible deadlock in rfcomm_sk_state_change Jiacheng Xu
2022-08-28 11:03 ` Jiacheng Xu
2022-08-30 6:48 ` Desmond Cheong Zhi Xi [this message]
2022-08-30 17:41 ` Luiz Augusto von Dentz
2022-08-30 19:23 ` Luiz Augusto von Dentz
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=f53dfd70-f8b3-8401-3f5a-d738b2f242e1@gmail.com \
--to=desmondcheongzx@gmail.com \
--cc=578001344xu@gmail.com \
--cc=davem@davemloft.net \
--cc=edumazet@google.com \
--cc=johan.hedberg@gmail.com \
--cc=kuba@kernel.org \
--cc=linux-bluetooth@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luiz.dentz@gmail.com \
--cc=marcel@holtmann.org \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).