________________________________________ From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> Sent: Wednesday, 21 July 2021 15:08 To: Zhang, Qiang Cc: stern@xxxxxxxxxxxxxxxxxxx; dvyukov@xxxxxxxxxx; paulmck@xxxxxxxxxx; dpenkler@xxxxxxxxx; guido.kiener@xxxxxxxxxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx 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@xxxxxxxxxxxxx wrote: > From: Zqiang <qiang.zhang@xxxxxxxxxxxxx> >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@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxxxxxx> >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. Thanks Qiang > >thanks, > >greg k-h
