On Wed, Jul 21, 2021 at 11:44:23AM +0200, dave penkler wrote: > On Wed, 21 Jul 2021 at 09:52, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Wed, Jul 21, 2021 at 09:41:15AM +0200, dave penkler wrote: > > > 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. > > > > I do not understand, is this change ok or not? > > > > Why do usbtmc applications need to know if babbling happens or not? > > > > confused, > Sorry, the issue this patch is trying to fix occurs because the > current usbtmc driver resubmits the URB when it gets an EPROTO return. > The dummy usb host controller driver used in the syzbot tests keeps > returning the resubmitted URB with EPROTO causing a loop that starves > RCU. With an actual HCI driver it either recovers or returns an EPIPE. > In either case no loop occurs. So for my part as a user and maintainer > this patch is not ok. Thanks for the review. Zqiang, can you fix this patch up based on this please? thanks, greg k-h
