On Tue, 2 May 2017, Mathias Nyman wrote:
> On 01.05.2017 22:41, Alan Stern wrote:
> > With threaded interrupts, bottom-half handlers are called with
> > interrupts enabled. Therefore they can't safely use spin_lock(); they
> > have to use spin_lock_irqsave(). Lockdep warns about a violation
> > occurring in xhci_irq():
> >
> > =========================================================
> > [ INFO: possible irq lock inversion dependency detected ]
> > 4.11.0-rc8-dbg+ #1 Not tainted
> > ---------------------------------------------------------
> > swapper/7/0 just changed the state of lock:
> > (&(&ehci->lock)->rlock){-.-...}, at: [<ffffffffa0130a69>]
> > ehci_hrtimer_func+0x29/0xc0 [ehci_hcd]
> > but this lock took another, HARDIRQ-unsafe lock in the past:
> > (hcd_urb_list_lock){+.....}
> >
> >
> > and interrupts could create inverse lock ordering between them.
> >
> > other info that might help us debug this:
> > Possible interrupt unsafe locking scenario:
> >
> > CPU0 CPU1
> > ---- ----
> > lock(hcd_urb_list_lock);
> > local_irq_disable();
> > lock(&(&ehci->lock)->rlock);
> > lock(hcd_urb_list_lock);
> > <Interrupt>
> > lock(&(&ehci->lock)->rlock);
> > *** DEADLOCK ***
> >
> > no locks held by swapper/7/0.
> > the shortest dependencies between 2nd lock and 1st lock:
> > -> (hcd_urb_list_lock){+.....} ops: 252 {
> > HARDIRQ-ON-W at:
> > __lock_acquire+0x602/0x1280
> > lock_acquire+0xd5/0x1c0
> > _raw_spin_lock+0x2f/0x40
> > usb_hcd_unlink_urb_from_ep+0x1b/0x60 [usbcore]
> > xhci_giveback_urb_in_irq.isra.45+0x70/0x1b0
> > [xhci_hcd]
> > finish_td.constprop.60+0x1d8/0x2e0 [xhci_hcd]
> > xhci_irq+0xdd6/0x1fa0 [xhci_hcd]
> > usb_hcd_irq+0x26/0x40 [usbcore]
> > irq_forced_thread_fn+0x2f/0x70
> > irq_thread+0x149/0x1d0
> > kthread+0x113/0x150
> > ret_from_fork+0x2e/0x40
> >
> > This patch fixes the problem.
> >
> > Signed-off-by: Alan Stern <[email protected]>
> > Reported-and-tested-by: Bart Van Assche <[email protected]>
> > CC: <[email protected]>
>
> Acked-by: Mathias Nyman <[email protected]>
Mathias, will you take this patch or should I send it to Greg?
Alan Stern
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