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

[Ryan Harper]

* Wen Congyang <address@hidden> [2011-02-27 20:56]:
> Hi Markus Armbruster
> 
> At 02/23/2011 04:30 PM, Markus Armbruster Write:
> > Isaku Yamahata <address@hidden> 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

How do you know that the guest has responded at this point before you
attempt to attach again at the top of the loop.  Any attach/detach
requires the guest to respond to the request and it may not respond at
all.


>    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 <address@hidden>
> 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.
> > 
> > 
> 

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
address@hidden