Subject: usb: dwc2: NMI watchdog: BUG: soft lockup - CPU#0 stuck for 146s

From: [email-masked] (Johan Hovold)
Date: Wed, 10 May 2017 18:31:50 +0200

On Mon, May 08, 2017 at 10:22:08PM +0200, Stefan Wahren wrote:
> 
> > Stefan Wahren <[email-masked]> hat am 25. April 2017 um 20:11 geschrieben:
> > 
> > 
> > > Stefan Wahren <[email-masked]> hat am 22. April 2017 um 22:50 geschrieben:
> > > 
> > > 
> > > Hi,
> > > 
> > > > Eric Anholt <[email-masked]> hat am 20. April 2017 um 20:54 geschrieben:
> > > > 
> > > > 
> > > > Stefan Wahren <[email-masked]> writes:
> > > > 
> > > > > Hi,
> > > > >
> > > > >> Doug Anderson <[email-masked]> hat am 18. April 2017 um 22:41 geschrieben:
> > > > >> 
> > > > >> 
> > > > >> It's hard to know for sure that all of this time is really in
> > > > >> urb_enqueue().  Possible we could have task switched out and been
> > > > >> blocked elsewhere.  Using ftrace to get more fine-grained timings
> > > > >> would be useful.  ktime_get(), ktime_sub(), and ktime_to_us() are your
> > > > >> friends here if you want to use trace_printk.
> > > > >
> > > > > i'm a newbie to ftrace, so i hope this would be helpful.
> > > > >
> > > > > # connect PL2303 to the onboard hub
> > > > > # echo 0 > options/sleep-time
> > > > > # echo 0 > function_profile_enabled
> > > > > # echo 1 > function_profile_enabled
> > > > > # ./usb_test
> > > > > # Waiting for at least 20 seconds and then disconnect PL2303
> > > > > # echo 0 > function_profile_enabled
> > > > > # cat trace_stat/function0
> > > > >
> > > > >   Function                               Hit    Time            Avg             s^2
> > > > >   --------                               ---    ----            ---             ---
> > > > >   bcm2835_handle_irq                  361347    219567633 us     607.636 us      1485199 us  
> > > > >   __handle_domain_irq                1082482    212639551 us     196.437 us      3642030 us  
> > > > >   generic_handle_irq                 1082482    100592051 us     92.927 us       50511334 us 
> > > > >   irq_exit                           1082482    98197771 us     90.715 us       29649040 us 
> > > > >   handle_level_irq                   1082482    95812379 us     88.511 us       51910093 us 
> > > > 
> > > > If I'm reading this output right, we're spending half of our interrupt
> > > > processing time in irq_exit(), so even if dwc2's interrupt was free (the
> > > > generic_handle_irq() chain), we'd be eating about half the CPU getting
> > > > back out of the interrupt handler, right?
> > > > 
> > > > I don't really know anything about DWC2 or USB, but is there any way we
> > > > could mitigate the interrupt frequency with this hardware?  If nothing
> > > > else, could we loop reading gintsts until it reads back 0?
> > > 
> > > first of all i updated my kernel to 4.11rc7 and the issue still
> > > occures. Today i had some time to investigate this issue further
> > > and i made some interesting observations:
> > > 
> > > 1. The lockup doesn't occure always after starting usb_test. In
> > > rare cases i was able to run the program without lockup.
> > > 2. In case the lockup occured we are always able to "rescue" the
> > > BCM2835 from this state by sending some serial data to the PL2303.
> > 
> > Based on this scenario i patched the interrupt routine to detect the
> > interrupt storm and normal condition. So i can dump the global and
> > host registers in both situations (bad and goodcase).
> > 
> > Here is the diff between both register dumps, maybe someone see
> > something interesting:
> > 
> > --- badcase.txt	2017-04-25 18:02:59.000000000 +0000
> > +++ goodcase.txt	2017-04-25 18:02:59.000000000 +0000
> > @@ -4,12 +4,12 @@
> >   dwc2_dump_global_registers: GAHBCFG	 @0xCC850008 : 0x00000031
> >   dwc2_dump_global_registers: GUSBCFG	 @0xCC85000C : 0x20001700
> >   dwc2_dump_global_registers: GRSTCTL	 @0xCC850010 : 0x80000000
> > - dwc2_dump_global_registers: GINTSTS	 @0xCC850014 : 0x06000021
> > + dwc2_dump_global_registers: GINTSTS	 @0xCC850014 : 0x06000029
> >   dwc2_dump_global_registers: GINTMSK	 @0xCC850018 : 0xF300080E
> > - dwc2_dump_global_registers: GRXSTSR	 @0xCC85001C : 0x00070044
> > + dwc2_dump_global_registers: GRXSTSR	 @0xCC85001C : 0x000F0001
> >   dwc2_dump_global_registers: GRXFSIZ	 @0xCC850024 : 0x00000306
> >   dwc2_dump_global_registers: GNPTXFSIZ	 @0xCC850028 : 0x01000306
> > - dwc2_dump_global_registers: GNPTXSTS	 @0xCC85002C : 0x1D080100
> > + dwc2_dump_global_registers: GNPTXSTS	 @0xCC85002C : 0x18080100
> > ...
> 
> @Doug, @John Y., @Johan: Any further ideas to narrow down the reason
> for this interrupt storm?

No, sorry.

I suggested earlier that you could try commenting out the interrupt-URB
submission in a naive attempt to narrow it down since that is an obvious
difference from the ftdi driver, but then again so are the frequent ftdi
status bulk messages (and any other timing differences).

Seems like you need to dig into dwc2.

Johan