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

[Greg KH <gregkh@linuxfoundation.org>]

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?

What about the usbtmc maintainers, what do they think about this?

thanks,

greg k-h