Re: [PATCH] usb: ehci: fix deadlock when threadirqs option is used

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On Wed, 19 Feb 2014, Stanislaw Gruszka wrote:

> ehci_irq() and ehci_hrtimer_func() can deadlock on ehci->lock when
> threadirqs option is used. To prevent the deadlock use
> spin_lock_irqsave() in ehci_irq().
> 
> This change can be reverted when hrtimer callbacks become threaded.
> 
> Signed-off-by: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
> ---
>  drivers/usb/host/ehci-hcd.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
> index 4711427..0bc6410 100644
> --- a/drivers/usb/host/ehci-hcd.c
> +++ b/drivers/usb/host/ehci-hcd.c
> @@ -685,8 +685,15 @@ static irqreturn_t ehci_irq (struct usb_hcd *hcd)
>  	struct ehci_hcd		*ehci = hcd_to_ehci (hcd);
>  	u32			status, masked_status, pcd_status = 0, cmd;
>  	int			bh;
> +	unsigned long		flags;
>  
> -	spin_lock (&ehci->lock);
> +	/*
> +	 * For threadirqs option we use spin_lock_irqsave() variant to prevent
> +	 * deadlock with ehci hrtimer callback, because hrtimer callbacks run
> +	 * in interrupt context even when threadirqs is specified. We can go
> +	 * back to spin_lock() variant when hrtimer callbacks become threaded.
> +	 */
> +	spin_lock_irqsave(&ehci->lock, flags);
>  
>  	status = ehci_readl(ehci, &ehci->regs->status);
>  
> @@ -704,7 +711,7 @@ static irqreturn_t ehci_irq (struct usb_hcd *hcd)
>  
>  	/* Shared IRQ? */
>  	if (!masked_status || unlikely(ehci->rh_state == EHCI_RH_HALTED)) {
> -		spin_unlock(&ehci->lock);
> +		spin_unlock_irqrestore(&ehci->lock, flags);
>  		return IRQ_NONE;
>  	}
>  
> @@ -815,7 +822,7 @@ dead:
>  
>  	if (bh)
>  		ehci_work (ehci);
> -	spin_unlock (&ehci->lock);
> +	spin_unlock_irqrestore(&ehci->lock, flags);
>  	if (pcd_status)
>  		usb_hcd_poll_rh_status(hcd);
>  	return IRQ_HANDLED;

Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>

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