Re: [PATCH] USB: usbtmc: Fix RCU stall warning

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jul 21, 2021 at 07:30:39AM +0000, Zhang, Qiang wrote:
> 
> 
> ________________________________________
> From: Greg KH <gregkh@linuxfoundation.org>
> Sent: Wednesday, 21 July 2021 15:08
> To: Zhang, Qiang
> Cc: stern@rowland.harvard.edu; dvyukov@google.com; paulmck@kernel.org; dpenkler@gmail.com; guido.kiener@rohde-schwarz.com; linux-usb@vger.kernel.org
> Subject: Re: [PATCH] USB: usbtmc: Fix RCU stall warning
> 
> [Please note: This e-mail is from an EXTERNAL e-mail address]
> 
> On Tue, Jun 29, 2021 at 11:32:36AM +0800, qiang.zhang@windriver.com wrote:
> > From: Zqiang <qiang.zhang@windriver.com>
> 
> >I need a "full" name here, and in the signed-off-by line please.
> 
> >
> > rcu: INFO: rcu_preempt self-detected stall on CPU
> > rcu:    1-...!: (2 ticks this GP) idle=d92/1/0x4000000000000000
> >         softirq=25390/25392 fqs=3
> >         (t=12164 jiffies g=31645 q=43226)
> > rcu: rcu_preempt kthread starved for 12162 jiffies! g31645 f0x0
> >      RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
> > rcu:    Unless rcu_preempt kthread gets sufficient CPU time,
> >         OOM is now expected behavior.
> > rcu: RCU grace-period kthread stack dump:
> > task:rcu_preempt     state:R  running task
> >
> > In the case of system use dummy_hcd as usb controller, when the
> > usbtmc devices is disconnected, in usbtmc_interrupt(), if the urb
> > status is unknown, the urb will be resubmit, the urb may be insert
> > to dum_hcd->urbp_list again, this will cause the dummy_timer() not
> > to exit for a long time, beacause the dummy_timer() be called in
> > softirq and local_bh is disable, this not only causes the RCU reading
> > critical area to consume too much time but also makes the tasks in
> > the current CPU runq not run in time, and that triggered RCU stall.
> >
> > return directly when find the urb status is not zero to fix it.
> >
> > Reported-by: syzbot+e2eae5639e7203360018@syzkaller.appspotmail.com
> > Signed-off-by: Zqiang <qiang.zhang@windriver.com>
> 
> >What commit does this fix?  Does it need to go to stable kernels?
> 
>  I will add fix tags resend,   need to go to stable kernel
> 
> >
> >What about the usbtmc maintainers, what do they think about this?
> 
>  Alan Stern reviewed this change before.

I do not see that on this commit :(