Messages in this thread Patch in this message | | | Date | Mon, 28 Jun 2021 10:17:51 -0400 | From | Alan Stern <> | Subject | Re: [syzbot] INFO: rcu detected stall in tx |
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On Mon, Jun 28, 2021 at 06:38:37AM +0000, Zhang, Qiang wrote: > > > ________________________________________ > From: Dmitry Vyukov <dvyukov@google.com> > Sent: Monday, 19 April 2021 15:27 > To: syzbot; Greg Kroah-Hartman; guido.kiener@rohde-schwarz.com; dpenkler@gmail.com; lee.jones@linaro.org; USB list > Cc: bp@alien8.de; dwmw@amazon.co.uk; hpa@zytor.com; linux-kernel@vger.kernel.org; luto@kernel.org; mingo@redhat.com; syzkaller-bugs@googlegroups.com; tglx@linutronix.de; x86@kernel.org > Subject: Re: [syzbot] INFO: rcu detected stall in tx > > [Please note: This e-mail is from an EXTERNAL e-mail address] > > On Mon, Apr 19, 2021 at 9:19 AM syzbot > <syzbot+e2eae5639e7203360018@syzkaller.appspotmail.com> wrote: > > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 50987bec Merge tag 'trace-v5.12-rc7' of git://git.kernel.o.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=1065c5fcd00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=398c4d0fe6f66e68 > > dashboard link: https://syzkaller.appspot.com/bug?extid=e2eae5639e7203360018 > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+e2eae5639e7203360018@syzkaller.appspotmail.com > > > > usbtmc 5-1:0.0: unknown status received: -71 > > usbtmc 3-1:0.0: unknown status received: -71 > > usbtmc 5-1:0.0: unknown status received: -71 > > >The log shows an infinite stream of these before the stall, so I > >assume it's an infinite loop in usbtmc. > >+usbtmc maintainers > > > >[ 370.171634][ C0] usbtmc 6-1:0.0: unknown status received: >-71 > >[ 370.177799][ C1] usbtmc 3-1:0.0: unknown status received: >-71
> This seems like a long time in the following cycle, when the callback function usbtmc_interrupt() find unknown status error, it will submit urb again. the urb may be insert urbp_list. > due to the dummy_timer() be called in bh-disable. > This will result in the RCU reading critical area not exiting for a long time (note: bh_disable/enable, preempt_disable/enable is regarded as the RCU critical reading area ), and prevent rcu_preempt kthread be schedule and running.
> Whether to return directly when we find the urb status is unknown error?
Yes.
> diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c > index 74d5a9c5238a..39d44339c03f 100644 > --- a/drivers/usb/class/usbtmc.c > +++ b/drivers/usb/class/usbtmc.c > @@ -2335,6 +2335,7 @@ static void usbtmc_interrupt(struct urb *urb) > return; > default: > dev_err(dev, "unknown status received: %d\n", status); > + return; > } > exit: > rv = usb_submit_urb(urb, GFP_ATOMIC);
This is the right thing to do. In fact, you should also change the code above this. There's no real need for special handling of the -ECONNRESET, -ENOENT, ..., -EPIPE codes, since the driver will do the same thing no matter what the code is.
Alan Stern
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