________________________________________ From: dave penkler <dpenkler@xxxxxxxxx> Sent: Wednesday, 21 July 2021 15:41 To: Greg KH Cc: Zhang, Qiang; Alan Stern; Dmitry Vyukov; paulmck@xxxxxxxxxx; Guido; USB Subject: Re: [PATCH] USB: usbtmc: Fix RCU stall warning [Please note: This e-mail is from an EXTERNAL e-mail address] On Wed, 21 Jul 2021 at 09:08, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > 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? > > What about the usbtmc maintainers, what do they think about this? >This patch makes the babbling endpoint retry/recovery code in the real >world usb host controller drivers redundant and would prevent usbtmc >applications from benefiting from it. Due to use dummy_hcd host, as explained earlier the RCU stall happens all the time, Is there a better way to solve it ？ Thanks Qiang > > thanks, > > greg k-h
