Re: [Qemu-devel] [PATCH] `qdev_free` when unplug a pci device

[Isaku Yamahata <yamahata@valinux.co.jp>]

On Tue, Mar 01, 2011 at 03:32:08PM +0800, Wen Congyang wrote:
> > The issue is, Qemu injected sci interrupt into guest,
> > but before the guest completes to handled it,
> > users/qemu can start to inject the next sci event triggered by hot plug/unplug.
> > Thus qemu loses sci interrupt and up/down status.
> 
> Yes, you are right. But I still do not understand why introducing pending bits
> can not solve the issue?

Maybe your patch works.
The difference is to introduce new variables or new state machine.

Anyway I suppose that the eventual solution is to switch to 
express native hotplug which is much more reliable and doesn't rely
on ACPI. (note: I'm very biased here.)

thanks

> 
> Thanks
> Wen Congyang
> 
> > 
> > thanks
> >>
> >>>
> >>> - on power-on  (0, 0)
> >>> - on hot plug  (0, 0) -> (1, 0)
> >>>                if other combination -> error
> >>> - on hot unpug (1, 0) or (0, 0) -> (0, 1)
> >>>                (0, 0) is for cold plugged devices.
> >>>                (1, 0) is for hot plugged devices.
> >>>                if other combination -> error
> >>> - on pciej_write(write on PCI_EJ_BASE)
> >>>                (0, 1) -> (0, 0) and qdev_free()
> >>>                if other combination -> ignore
> >>>
> >>> When enabling sci, those bits are checked and raise sci if necessary.
> >>>
> >>> Any comments on this?
> >>> Anyway the current pci hotplug-related commands are somewhat broken,
> >>> and needs clean up with multifunction hotplug support which is
> >>> on my todo list.
> >>>
> >>> thanks
> >>>
> >>> On Mon, Feb 28, 2011 at 10:52:40AM +0800, Wen Congyang wrote:
> >>>> Hi Markus Armbruster
> >>>>
> >>>> At 02/23/2011 04:30 PM, Markus Armbruster Write:
> >>>>> Isaku Yamahata <yamahata@valinux.co.jp> writes:
> >>>>>
> >>>>
> >>>> <snip>
> >>>>
> >>>>>
> >>>>> I don't think this patch is correct.  Let me explain.
> >>>>>
> >>>>> Device hot unplug is *not* guaranteed to succeed.
> >>>>>
> >>>>> For some buses, such as USB, it always succeeds immediately, i.e. when
> >>>>> the device_del monitor command finishes, the device is gone.  Live is
> >>>>> good.
> >>>>>
> >>>>> But for PCI, device_del merely initiates the ACPI unplug rain dance.  It
> >>>>> doesn't wait for the dance to complete.  Why?  The dance can take an
> >>>>> unpredictable amount of time, including forever.
> >>>>>
> >>>>> Problem: Subsequent device_add can fail if it reuses the qdev ID or PCI
> >>>>> slot, and the unplug has not yet completed (race condition), or it
> >>>>> failed.  Yes, Virginia, PCI hotplug *can* fail.
> >>>>>
> >>>>> When unplug succeeds, the qdev is automatically destroyed.
> >>>>> pciej_write() does that for PIIX4.  Looks like pcie_cap_slot_event()
> >>>>> does it for PCIE.
> >>>>
> >>>> I got a similar problem.  When I unplug a pci device by hand, it works
> >>>> as expected, and I can hotplug it again. But when I use a srcipt to
> >>>> do the same thing, sometimes it failed. I think I may find another bug.
> >>>>
> >>>> Steps to reproduce this bug:
> >>>> 1. cat ./test-e1000.sh # RHEL6RC is domain name
> >>>>    #! /bin/bash
> >>>>
> >>>>    while true; do
> >>>>            virsh attach-interface RHEL6RC network default --mac 52:54:00:1f:db:c7 --model e1000
> >>>>            if [[ $? -ne 0 ]]; then
> >>>>                    break
> >>>>            fi
> >>>>            virsh detach-interface RHEL6RC network --mac 52:54:00:1f:db:c7
> >>>>            if [[ $? -ne 0 ]]; then
> >>>>                    break
> >>>>            fi
> >>>>            sleep 5
> >>>>    done
> >>>>
> >>>> 2. ./test-e1000.sh
> >>>>    Interface attached successfully
> >>>>
> >>>>    Interface detached successfully
> >>>>
> >>>>    Interface attached successfully
> >>>>
> >>>>    Interface detached successfully
> >>>>
> >>>>    error: Failed to attach interface
> >>>>    error: operation failed: adding e1000,netdev=hostnet1,id=net1,mac=52:54:00:1f:db:c7,bus=pci.0,addr=0x8 device failed: Duplicate ID 'net1' for device
> >>>>
> >>>>
> >>>> I use ftrace to trace whether sci interrupt is passed to guest OS, here is log:
> >>>> # cat trace | grep 'irq=9'
> >>>>           <idle>-0     [000] 118342.634772: irq_handler_entry: irq=9 name=acpi
> >>>>           <idle>-0     [000] 118342.634831: irq_handler_exit: irq=9 ret=handled
> >>>>           <idle>-0     [000] 118342.693216: irq_handler_entry: irq=9 name=acpi
> >>>>           <idle>-0     [000] 118342.693254: irq_handler_exit: irq=9 ret=handled
> >>>>           <idle>-0     [000] 118347.737689: irq_handler_entry: irq=9 name=acpi
> >>>>           <idle>-0     [000] 118347.737738: irq_handler_exit: irq=9 ret=handled
> >>>> According to the log, we only receive 3 sci interrupt, and one is lost.
> >>>>
> >>>> I enable piix4's debug and 1 line printf into piix4_device_hotplug:
> >>>>     printf("slot: %d, up: %d, down: %d, state: %d\n", slot, s->pci0_status.up, s->pci0_status.down, state);
> >>>> here is the log:
> >>>> ========
> >>>> PM: mapping to 0xb000
> >>>> PM readw port=0x0004 val=0x0000
> >>>> ...
> >>>> gpe write afe2 <== 0
> >>>> gpe write afe0 <== 255
> >>>> gpe write afe3 <== 0
> >>>> gpe write afe1 <== 255
> >>>> PM readw port=0x0000 val=0x0001
> >>>> PM readw port=0x0002 val=0x0000
> >>>> gpe read afe0 == 0
> >>>> gpe read afe2 == 0
> >>>> gpe read afe1 == 0
> >>>> gpe read afe3 == 0
> >>>> PM writew port=0x0000 val=0x0020
> >>>> PM readw port=0x0002 val=0x0000
> >>>> PM writew port=0x0002 val=0x0020
> >>>> PM readw port=0x0002 val=0x0020
> >>>> gpe write afe2 <== 255
> >>>> gpe write afe3 <== 255
> >>>> ...
> >>>> slot: 6, up: 0, down: 0, state: 1   <==== we attach interface the first time
> >>>> PM readw port=0x0000 val=0x0001
> >>>> PM readw port=0x0002 val=0x0120
> >>>> gpe read afe0 == 2
> >>>> gpe read afe2 == ff
> >>>> gpe read afe2 == ff
> >>>> gpe write afe2 <== 253
> >>>> gpe read afe1 == 0
> >>>> gpe read afe3 == ff
> >>>> pcihotplug read ae00 == 40
> >>>> pcihotplug read ae04 == 0
> >>>> ...
> >>>> gpe write afe0 <== 2
> >>>> gpe write afe2 <== 255
> >>>> slot: 6, up: 64, down: 0, state: 0  <===== we detach interface the first time
> >>>> PM readw port=0x0000 val=0x0001
> >>>> PM readw port=0x0002 val=0x0120
> >>>> gpe read afe0 == 2
> >>>> gpe read afe2 == ff
> >>>> gpe read afe2 == ff
> >>>> gpe write afe2 <== 253
> >>>> gpe read afe1 == 0
> >>>> gpe read afe3 == ff
> >>>> pcihotplug read ae00 == 0
> >>>> pcihotplug read ae04 == 40
> >>>> ...
> >>>> pciej write ae08 <== 64		<=== we will call qdev_free()
> >>>> pciej write ae08 <== 64
> >>>> gpe write afe0 <== 2
> >>>> gpe write afe2 <== 255
> >>>> slot: 7, up: 0, down: 64, state: 1  <=== we attach interface the second time.
> >>>> PM readw port=0x0000 val=0x0001
> >>>> PM readw port=0x0002 val=0x0120
> >>>> gpe read afe0 == 2
> >>>> gpe read afe2 == ff
> >>>> gpe read afe2 == ff
> >>>> gpe write afe2 <== 253
> >>>> gpe read afe1 == 0
> >>>> gpe read afe3 == ff
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> pcihotplug read ae00 == 80
> >>>> pcihotplug read ae04 == 0
> >>>> slot: 7, up: 128, down: 0, state: 0  <=== we detach interface the second time
> >>>> gpe write afe0 <== 2		<=== write 2 to afe0 will cause sci interupt to be lost
> >>>> gpe write afe2 <== 255
> >>>> ===========
> >>>>
> >>>> Here is short log, and show the different between the first time and second time:
> >>>> ===========
> >>>> gpe write afe0 <== 2
> >>>> gpe write afe2 <== 255
> >>>> slot: 6, up: 64, down: 0, state: 0  <===== we detach interface the first time
> >>>> ....
> >>>> slot: 7, up: 128, down: 0, state: 0  <=== we detach interface the second time
> >>>> gpe write afe0 <== 2		<=== write 2 to afe0 will cause sci interupt to be lost
> >>>> gpe write afe2 <== 255
> >>>>
> >>>> ===========
> >>>>
> >>>> Does this behavior is a normal behavior?
> >>>>
> >>>> The following patch can fix this problem.
> >>>>
> >>>> From 3c149575b52261b8da9a73d5c4ebdfedce9866c1 Mon Sep 17 00:00:00 2001
> >>>> From: Wen Congyang <wency@cn.fujitsu.com>
> >>>> Date: Mon, 28 Feb 2011 10:33:45 +0800
> >>>> Subject: [PATCH] pend hotplug event until last event is handled by guest OS
> >>>>
> >>>> ---
> >>>>  hw/acpi_piix4.c |   51 ++++++++++++++++++++++++++++++++++++++++++++-------
> >>>>  1 files changed, 44 insertions(+), 7 deletions(-)
> >>>>
> >>>> diff --git a/hw/acpi_piix4.c b/hw/acpi_piix4.c
> >>>> index b5a2762..4ff3475 100644
> >>>> --- a/hw/acpi_piix4.c
> >>>> +++ b/hw/acpi_piix4.c
> >>>> @@ -74,6 +74,7 @@ typedef struct PIIX4PMState {
> >>>>      /* for pci hotplug */
> >>>>      struct gpe_regs gpe;
> >>>>      struct pci_status pci0_status;
> >>>> +    struct pci_status pci0_status_pending;
> >>>>      uint32_t pci0_hotplug_enable;
> >>>>  } PIIX4PMState;
> >>>>  
> >>>> @@ -518,6 +519,19 @@ static void gpe_reset_val(uint16_t *cur, int addr, uint32_t val)
> >>>>      *cur = (*cur & (0xff << (8 - shift))) | (x1 << shift);
> >>>>  }
> >>>>  
> >>>> +static void raise_pending_hotplug(PIIX4PMState *s)
> >>>> +{
> >>>> +    if (s->pci0_status_pending.up || s->pci0_status_pending.down) {
> >>>> +        s->gpe.sts |= PIIX4_PCI_HOTPLUG_STATUS;
> >>>> +        s->pci0_status.up = s->pci0_status_pending.up;
> >>>> +        s->pci0_status.down = s->pci0_status_pending.down;
> >>>> +        s->pci0_status_pending.up = 0;
> >>>> +        s->pci0_status_pending.down = 0;
> >>>> +
> >>>> +        pm_update_sci(s);
> >>>> +    }
> >>>> +}
> >>>> +
> >>>>  static void gpe_writeb(void *opaque, uint32_t addr, uint32_t val)
> >>>>  {
> >>>>      PIIX4PMState *s = opaque;
> >>>> @@ -539,6 +553,11 @@ static void gpe_writeb(void *opaque, uint32_t addr, uint32_t val)
> >>>>      pm_update_sci(s);
> >>>>  
> >>>>      PIIX4_DPRINTF("gpe write %x <== %d\n", addr, val);
> >>>> +
> >>>> +    if (!(g->sts & PIIX4_PCI_HOTPLUG_STATUS) && g->en & PIIX4_PCI_HOTPLUG_STATUS) {
> >>>> +        /* check and reraise the pending hotplug event */
> >>>> +        raise_pending_hotplug(s);
> >>>> +    }
> >>>>  }
> >>>>  
> >>>>  static uint32_t pcihotplug_read(void *opaque, uint32_t addr)
> >>>> @@ -639,12 +658,22 @@ static void enable_device(PIIX4PMState *s, int slot)
> >>>>      s->pci0_status.up |= (1 << slot);
> >>>>  }
> >>>>  
> >>>> +static void pend_enable_device(PIIX4PMState *s, int slot)
> >>>> +{
> >>>> +    s->pci0_status_pending.up |= (1 << slot);
> >>>> +}
> >>>> +
> >>>>  static void disable_device(PIIX4PMState *s, int slot)
> >>>>  {
> >>>>      s->gpe.sts |= PIIX4_PCI_HOTPLUG_STATUS;
> >>>>      s->pci0_status.down |= (1 << slot);
> >>>>  }
> >>>>  
> >>>> +static void pend_disable_device(PIIX4PMState *s, int slot)
> >>>> +{
> >>>> +    s->pci0_status_pending.down |= (1 << slot);
> >>>> +}
> >>>> +
> >>>>  static int piix4_device_hotplug(DeviceState *qdev, PCIDevice *dev,
> >>>>  				PCIHotplugState state)
> >>>>  {
> >>>> @@ -659,15 +688,23 @@ static int piix4_device_hotplug(DeviceState *qdev, PCIDevice *dev,
> >>>>          return 0;
> >>>>      }
> >>>>  
> >>>> -    s->pci0_status.up = 0;
> >>>> -    s->pci0_status.down = 0;
> >>>> -    if (state == PCI_HOTPLUG_ENABLED) {
> >>>> -        enable_device(s, slot);
> >>>> +    if (s->gpe.sts & PIIX4_PCI_HOTPLUG_STATUS) {
> >>>> +        if (state == PCI_HOTPLUG_ENABLED) {
> >>>> +            pend_enable_device(s, slot);
> >>>> +        } else {
> >>>> +            pend_disable_device(s, slot);
> >>>> +        }
> >>>>      } else {
> >>>> -        disable_device(s, slot);
> >>>> -    }
> >>>> +        s->pci0_status.up = 0;
> >>>> +        s->pci0_status.down = 0;
> >>>> +        if (state == PCI_HOTPLUG_ENABLED) {
> >>>> +            enable_device(s, slot);
> >>>> +        } else {
> >>>> +            disable_device(s, slot);
> >>>> +        }
> >>>>  
> >>>> -    pm_update_sci(s);
> >>>> +        pm_update_sci(s);
> >>>> +    }
> >>>>  
> >>>>      return 0;
> >>>>  }
> >>>> -- 
> >>>> 1.7.1
> >>>>
> >>>>>
> >>>>> Your patch adds a *second* qdev_free().  No good.
> >>>>>
> >>>>>
> >>>>
> >>>>
> >>>
> >>
> > 
> 

-- 
yamahata