On Wed, Aug 17, 2016 at 10:12 AM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> Hi Mayurkumar,
>
> On Wed, Aug 17, 2016 at 01:42:18PM +0000, Patel, Mayurkumar wrote:
> > Currently, if very fast hotplug removal and insertion event comes
> > as following
> >
> > [ 608.823412] pciehp 0000:00:1c.1:pcie04: Card not present on Slot(1)
> > [ 608.835249] pciehp 0000:00:1c.1:pcie04: Card present on Slot(1)
> >
> > In this case following scenario happens,
> >
> > While removal:
> > pcie_isr() -> pciehp_queue_interrupt_event() -> triggers queue_work().
> > work invokes interrupt_event_handler() -> case INT_PRESENCE_OFF
> > and calls handle_surprise_event().
> >
> > handle_surprise_event() again calls pciehp_get_adapter_status()
> > and reads slot status which might have been changed
> > already due to PCI_EXP_SLTSTA_PDC event for hotplug insertion
> > has happened. So it queues, ENABLE_REQ for both removal
> > and insertion interrupt based on latest slot status.
> >
> > In this case, PCIe device can not be hot-add again because
> > it was never removed due to which device can not get enabled.
> >
> > handle_surprise_event() can be removed and pciehp_queue_power_work()
> > can be directly triggered based on INT_PRESENCE_ON and INT_PRESENCE_OFF
> > from the switch case exist in interrupt_event_hanlder().
> >
> > The patch ensures the pciehp_queue_power_work() processes
> > presence detect change for removal and insertion correctly.
> >
> > Signed-off-by: Mayurkumar Patel <mayurkumar.patel@xxxxxxxxx>
Acked-by: Rajat Jain <rajatxjain@xxxxxxxxx>
>
> > ---
> > Resending the patch addressing to PCI Maintainer Bjorn Helgaas.
> >
> > drivers/pci/hotplug/pciehp_ctrl.c | 18 ++----------------
> > 1 file changed, 2 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> > index 880978b..87c5bea 100644
> > --- a/drivers/pci/hotplug/pciehp_ctrl.c
> > +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> > @@ -301,20 +301,6 @@ static void handle_button_press_event(struct slot *p_slot)
> > /*
> > * Note: This function must be called with slot->lock held
> > */
> > -static void handle_surprise_event(struct slot *p_slot)
> > -{
> > - u8 getstatus;
> > -
> > - pciehp_get_adapter_status(p_slot, &getstatus);
> > - if (!getstatus)
> > - pciehp_queue_power_work(p_slot, DISABLE_REQ);
> > - else
> > - pciehp_queue_power_work(p_slot, ENABLE_REQ);
> > -}
> > -
> > -/*
> > - * Note: This function must be called with slot->lock held
> > - */
> > static void handle_link_event(struct slot *p_slot, u32 event)
> > {
> > struct controller *ctrl = p_slot->ctrl;
> > @@ -377,14 +363,14 @@ static void interrupt_event_handler(struct work_struct *work)
> > pciehp_green_led_off(p_slot);
> > break;
> > case INT_PRESENCE_ON:
> > - handle_surprise_event(p_slot);
> > + pciehp_queue_power_work(p_slot, ENABLE_REQ);
> > break;
> > case INT_PRESENCE_OFF:
> > /*
> > * Regardless of surprise capability, we need to
> > * definitely remove a card that has been pulled out!
> > */
> > - handle_surprise_event(p_slot);
> > + pciehp_queue_power_work(p_slot, DISABLE_REQ);
> > break;
> > case INT_LINK_UP:
> > case INT_LINK_DOWN:
>
> Thanks a lot for this. I think other people have seen the same issue.
>
> Even with this fix, don't we have essentially the same problem one
> layer back? The first thing pcie_isr() does is read PCI_EXP_SLTSTA,
> then few lines down, we call pciehp_get_adapter_status(), which reads
> PCI_EXP_SLTSTA *again*. So I think the window is smaller but still
> there.
>
> I think what we really should do is read the status registers
> (PCI_EXP_SLTSTA and probably also PCI_EXP_LNKSTA) *once* in
> pcie_isr(), before we write PCI_EXP_SLTSTA to clear the RW1C bits
> there, and then queue up events based on those values, without
> re-reading the registers.
>
> What do you think?
Yes, I agree. We need to do something about that *in addition * to the
above patch to cover the
whole story. However I think there still will be a room for some
interrupt misses because we are
collecting the interrupts in intr_loc, and theoretically we could be
in a situation where in the pcie_isr, the
do {
...
} while(detected)
loop gets a removal->insertion->removal all while in the same
invocation of pcie_isr().
If this happens, the intr_loc will have recorded a single insertion
and a single removal, and
the final result will depend on the order in which we decide to
process the events in intr_loc.
Or, may be we can make the calls to pciehp_queue_interrupt_event()
before clearing the
RW1C in the slot status register (in the loop)?
Thanks,
rajat
>
>
> Bjorn
> --
> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-pci" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
