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SubjectRe: OHCI root_port_reset() deadly loop...
> Regardless, here is a patch that hardens the OHCI reset handling
> loops so that they break out instead of hanging the entire system
> should this condition occur. It's at least better than what the
> code does to a user right now which is hang the box completely:
>
> [USB] ohci: Do not hang the system if port reset does not complete.
>
> Signed-off-by: David S. Miller <davem@davemloft.net>
>
> diff --git a/drivers/usb/host/ohci-hub.c b/drivers/usb/host/ohci-hub.c
> index bb9cc59..77ae5b4 100644
> --- a/drivers/usb/host/ohci-hub.c
> +++ b/drivers/usb/host/ohci-hub.c
> @@ -563,14 +563,19 @@ static inline int root_port_reset (struct ohci_hcd *ohci, unsigned port)
> u32 temp;
> u16 now = ohci_readl(ohci, &ohci->regs->fmnumber);
> u16 reset_done = now + PORT_RESET_MSEC;
> + int limit_1;
>
> /* build a "continuous enough" reset signal, with up to
> * 3msec gap between pulses. scheduler HZ==100 must work;
> * this might need to be deadline-scheduled.
> */
> - do {
> + limit_1 = 100;
> + while (--limit_1 >= 0) {

Don't need this "limit_1" timeout; "reset_done" handles all
the timeout needed there. The regs->fmnumber is essentially
a millisecond counter.


> + int limit_2;
> +
> /* spin until any current reset finishes */
> - for (;;) {
> + limit_2 = PORT_RESET_MSEC * 2;

This is the loop that didn't terminate for you, right?
PORT_RESET_HW_MSEC is the ceiling you should use here,
not PORT_RESET_MSEC.


> + while (--limit_2 >= 0) {
> temp = ohci_readl (ohci, portstat);
> /* handle e.g. CardBus eject */
> if (temp == ~(u32)0)
> @@ -579,6 +584,10 @@ static inline int root_port_reset (struct ohci_hcd *ohci, unsigned port)
> break;
> udelay (500);
> }
> + if (limit_2 < 0) {
> + ohci_warn(ohci, "Root port inner-loop reset timeout, "
> + "portstat[%08x]\n", temp);
> + }

What values do you see for "portstat"?

I suspect there will be some flag set which would allow a more
immediate exit from that loop. RH_PS_CCS might clear, for example.

And in any case, if that fails I don't see any reason not to just
break, and return immediately.

>
> if (!(temp & RH_PS_CCS))
> break;
> @@ -589,7 +598,14 @@ static inline int root_port_reset (struct ohci_hcd *ohci, unsigned port)
> ohci_writel (ohci, RH_PS_PRS, portstat);
> msleep(PORT_RESET_HW_MSEC);
> now = ohci_readl(ohci, &ohci->regs->fmnumber);
> - } while (tick_before(now, reset_done));
> + if (!tick_before(now, reset_done))
> + break;
> + }
> + if (limit_1 < 0) {
> + ohci_warn(ohci, "Root port outer-loop reset timeout, "
> + "now[%04x] reset_done[%04x]\n",
> + now, reset_done);
> + }
> /* caller synchronizes using PRSC */
>
> return 0;
>
-
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