RE: [PATCH] usb: host: ohci: fix a race condition between shutdown and irq

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Hi Alan,

> From: Alan Stern, Sent: Tuesday, August 27, 2019 12:58 AM
> 
> On Mon, 26 Aug 2019, Yoshihiro Shimoda wrote:
> 
> > Hi Alan,
> >
> > > From: Alan Stern, Sent: Saturday, August 24, 2019 12:33 AM
> > >
> > > On Fri, 23 Aug 2019, Yoshihiro Shimoda wrote:
<snip>
> > > > The ohci_shutdown() should hold the spin lock while disabling
> > > > the interruption and changing the rh_state flag. Note that
> > > > io_watchdog_func() also calls the ohci_shutdown() and it
> > > > already held the spin lock, so that the patch makes a new
> > > > function as _ohci_shutdown().
> > >
> > > I don't understand this description.  It sounds like the OHCI
> > > controller generates an interrupt request, and then ohci_shutdown()
> > > disables the interrupt request before the handler can run.  When the
> > > handler does run, it sees that no interrupts are enabled and so it
> > > returns IRQ_NOTMINE, leading to the error shown above.
> > >
> > > How will holding the spinlock fix this problem?
> >
> > I'm sorry for lacking description. I should have described the following
> > descriptions instead of that. What do you think?
> >
> > --
> > ohci_shutdown() disables all the interrupt and rh_state is set to
> > OHCI_RH_HALTED. In other hand, ohci_irq() is possible to enable
> > OHCI_INTR_SF and OHCI_INTR_MIE on ohci_irq(). Note that OHCI_INTR_SF
> > is possible to be set by start_ed_unlink() which is called:
> >  ohci_irq()
> >   -> process_done_list()
> >    -> takeback_td()
> >     -> start_ed_unlink()
> >
> > So, ohci_irq() has the following condition, the issue happens by
> > &ohci->regs->intrenable = OHCI_INTR_MIE | OHCI_INTR_SF and
> > ohci->rh_state = OHCI_RH_HALTED:
> >
> > 	/* interrupt for some other device? */
> > 	if (ints == 0 || unlikely(ohci->rh_state == OHCI_RH_HALTED))
> > 		return IRQ_NOTMINE;
> >
> > To fix the issue, ohci_shutdown() holds the spin lock while disabling
> > the interruption and changing the rh_state flag to prevent reenable
> > the OHCI_INTR_MIE unexpectedly. Note that io_watchdog_func() also calls
> > the ohci_shutdown() and it already held the spin lock, so that the patch
> > makes a new function as _ohci_shutdown().
> 
> Okay, that's a lot better.  Please resubmit the patch with the new
> description.

Thank you for your review! I have submitted v2 patch as the following:
https://patchwork.kernel.org/patch/11115947/

Best regards,
Yoshihiro Shimoda





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