netdev - Re: [PATCH v2 net-next 06/14] netlink: hold nlk->cb_mutex longer in __netlink_dump

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Date: Mon, 10 Jun 2024 14:59:19 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Dmitry Vyukov <dvyukov@...gle.com>
Cc: Jiri Pirko <jiri@...nulli.us>, "David S . Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	Ido Schimmel <idosch@...dia.com>, Jiri Pirko <jiri@...dia.com>, eric.dumazet@...il.com
Subject: Re: [PATCH v2 net-next 06/14] netlink: hold nlk->cb_mutex longer in __netlink_dump_start()

On Sun, Jun 9, 2024 at 10:29 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> On 2024/06/09 17:17, Tetsuo Handa wrote:
> > Hello.
> >
> > While investigating hung task reports involving rtnl_mutex, I came to
> > suspect that commit b5590270068c ("netlink: hold nlk->cb_mutex longer
> > in __netlink_dump_start()") is buggy, for that commit made only
> > mutex_lock(nlk->cb_mutex) side conditionally. Why don't we need to make
> > mutex_unlock(nlk->cb_mutex) side conditionally?
> >
>
> Sorry for the noise. That commit should be correct, for the caller
> no longer calls mutex_unlock(nlk->cb_mutex).
>
> I'll try a debug printk() patch for linux-next.

I also have a lot of hung task reports as well, but in most reports
the console is flooded
before the crashes.


[  276.515597][    C1] yealink 4-1:36.0: urb_ctl_callback - urb status -71
[  276.522774][    C1] yealink 4-1:36.0: urb_irq_callback - urb status -71
[  276.529566][    C1] yealink 4-1:36.0: unexpected response 0
[  276.535875][    C1] yealink 4-1:36.0: urb_ctl_callback - urb status -71
[  276.543011][    C1] yealink 4-1:36.0: urb_irq_callback - urb status -71
[  276.549951][    C1] yealink 4-1:36.0: unexpected response 0
[  276.556111][    C1] yealink 4-1:36.0: urb_ctl_callback - urb status -71
[  276.563143][    C1] yealink 4-1:36.0: urb_irq_callback - urb status -71
[  276.570382][    C1] yealink 4-1:36.0: unexpected response 0
[  276.576399][    C1] yealink 4-1:36.0: urb_ctl_callback - urb status -71
[  276.584381][    C1] yealink 4-1:36.0: urb_irq_callback - urb status -71
[  276.591617][    C1] yealink 4-1:36.0: unexpected response 0
[  276.597904][    C1] yealink 4-1:36.0: urb_ctl_callback - urb status -71
[  276.605126][    C1] yealink 4-1:36.0: urb_irq_callback - urb status -71
[  276.612153][    C1] yealink 4-1:36.0: unexpected response 0
[  276.618588][    C1] yealink 4-1:36.0: urb_ctl_callback - urb status -71
[  276.626153][    C1] yealink 4-1:36.0: urb_irq_callback - urb status -71
[  276.631595][   T30] INFO: task dhcpcd:4749 blocked for more than 143 seconds.
[  276.633015][    C1] yealink 4-1:36.0: unexpected response 0
[  276.646813][    C1] yealink 4-1:36.0: urb_ctl_callback - urb status -71
[  276.654401][   T30]       Not tainted
6.10.0-rc2-syzkaller-00269-g96e09b8f8166 #0


2024/06/08 02:48:35 SYZFATAL: failed to recv *flatrpc.HostMessageRaw: EOF

[  276.654461][    C1] yealink 4-1:36.0: urb_irq_callback - urb status -71

I wonder how to deal with SYZFATAL, maybe the reports are truncated and we
do not see who owns rtnl mutex.