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Re: [Qemu-devel] [PATCH v2 2/2] vfio : add aer process

Started by	Alex Williamson <alex.williamson@redhat.com>
First post	2016-07-29 19:20 +0200
Last post	2016-08-02 03:30 +0200
Articles	4 — 2 participants

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  Re: [Qemu-devel] [PATCH v2 2/2] vfio : add aer process Alex Williamson <alex.williamson@redhat.com> - 2016-07-29 19:20 +0200
    Re: [Qemu-devel] [PATCH v2 2/2] vfio : add aer process Zhou Jie <zhoujie2011@cn.fujitsu.com> - 2016-08-01 04:20 +0200
      Re: [Qemu-devel] [PATCH v2 2/2] vfio : add aer process Alex Williamson <alex.williamson@redhat.com> - 2016-08-01 17:40 +0200
        Re: [Qemu-devel] [PATCH v2 2/2] vfio : add aer process Zhou Jie <zhoujie2011@cn.fujitsu.com> - 2016-08-02 03:30 +0200

#1452485 — Re: [Qemu-devel] [PATCH v2 2/2] vfio : add aer process

From	Alex Williamson <alex.williamson@redhat.com>
Date	2016-07-29 19:20 +0200
Subject	Re: [Qemu-devel] [PATCH v2 2/2] vfio : add aer process
Message-ID	<s0jC2-7Er-5@gated-at.bofh.it>

On Tue, 19 Jul 2016 15:32:43 +0800
Zhou Jie <zhoujie2011@cn.fujitsu.com> wrote:

> From: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> 
> During aer err occurs and resume do following to
> protect device from being accessed.
> 1. Make config space read only.
> 2. Disable INTx/MSI Interrupt.
> 3. Do nothing for bar regions.
> 
> Signed-off-by: Zhou Jie <zhoujie2011@cn.fujitsu.com>
> ---
>  drivers/vfio/pci/vfio_pci.c         | 30 ++++++++++++++++++++++++++++++
>  drivers/vfio/pci/vfio_pci_private.h |  2 ++
>  include/uapi/linux/vfio.h           |  2 ++
>  3 files changed, 34 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 2d12b03..dd96b60 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -318,6 +318,7 @@ static int vfio_pci_open(void *device_data)
>  		return -ENODEV;
>  
>  	mutex_lock(&driver_lock);
> +	init_completion(&vdev->aer_error_completion);
>  
>  	if (!vdev->refcnt) {
>  		ret = vfio_pci_enable(vdev);
> @@ -571,6 +572,16 @@ static long vfio_pci_ioctl(void *device_data,
>  	struct vfio_pci_device *vdev = device_data;
>  	unsigned long minsz;
>  
> +	if (vdev->aer_error_in_progress && (cmd == VFIO_DEVICE_SET_IRQS ||
> +	    cmd == VFIO_DEVICE_RESET || cmd == VFIO_DEVICE_PCI_HOT_RESET)) {
> +		int ret;
> +		ret = wait_for_completion_interruptible(
> +			&vdev->aer_error_completion);
> +		if (ret) {
> +			return ret;
> +		}

No brackets necessary.

> +	}
> +
>  	if (cmd == VFIO_DEVICE_GET_INFO) {
>  		struct vfio_device_info info;
>  
> @@ -587,6 +598,10 @@ static long vfio_pci_ioctl(void *device_data,
>  		if (vdev->reset_works)
>  			info.flags |= VFIO_DEVICE_FLAGS_RESET;
>  
> +		info.flags |= VFIO_DEVICE_FLAGS_AERPROCESS;
> +		if (vdev->aer_error_in_progress)
> +			info.flags |= VFIO_DEVICE_FLAGS_INAERPROCESS;
> +
>  		info.num_regions = VFIO_PCI_NUM_REGIONS + vdev->num_regions;
>  		info.num_irqs = VFIO_PCI_NUM_IRQS;
>  
> @@ -996,6 +1011,14 @@ static ssize_t vfio_pci_rw(void *device_data, char __user *buf,
>  
>  	switch (index) {
>  	case VFIO_PCI_CONFIG_REGION_INDEX:
> +		if (vdev->aer_error_in_progress && iswrite) {
> +			int ret;
> +			ret = wait_for_completion_interruptible(
> +				&vdev->aer_error_completion);
> +			if (ret) {
> +				return ret;
> +			}
> +		}
>  		return vfio_pci_config_rw(vdev, buf, count, ppos, iswrite);
>  
>  	case VFIO_PCI_ROM_REGION_INDEX:
> @@ -1226,6 +1249,10 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
>  
>  	mutex_lock(&vdev->igate);
>  
> +	vdev->aer_error_in_progress = true;
> +	vfio_pci_set_irqs_ioctl(vdev, VFIO_IRQ_SET_DATA_NONE |
> +				VFIO_IRQ_SET_ACTION_TRIGGER,
> +				vdev->irq_type, 0, 0, NULL);
>  	if (vdev->err_trigger)
>  		eventfd_signal(vdev->err_trigger, 1);
>  
> @@ -1252,6 +1279,9 @@ static void vfio_pci_aer_resume(struct pci_dev *pdev)
>  	}
>  
>  	mutex_lock(&vdev->igate);
> +
> +	vdev->aer_error_in_progress = false;
> +	complete_all(&vdev->aer_error_completion);
>  	if (vdev->resume_trigger)
>  		eventfd_signal(vdev->resume_trigger, 1);
>  
> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> index 80d4ddd..2f151f5 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -84,6 +84,8 @@ struct vfio_pci_device {
>  	bool			has_vga;
>  	bool			needs_reset;
>  	bool			nointx;
> +	bool			aer_error_in_progress;
> +	struct completion	aer_error_completion;
>  	struct pci_saved_state	*pci_saved_state;
>  	int			refcnt;
>  	struct eventfd_ctx	*err_trigger;
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 34ab138..276ce50 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -198,6 +198,8 @@ struct vfio_device_info {
>  #define VFIO_DEVICE_FLAGS_PCI	(1 << 1)	/* vfio-pci device */
>  #define VFIO_DEVICE_FLAGS_PLATFORM (1 << 2)	/* vfio-platform device */
>  #define VFIO_DEVICE_FLAGS_AMBA  (1 << 3)	/* vfio-amba device */
> +#define VFIO_DEVICE_FLAGS_AERPROCESS  (1 << 4)	/* support aer error progress */
> +#define VFIO_DEVICE_FLAGS_INAERPROCESS  (1 << 5)/* status in aer error progress */
>  	__u32	num_regions;	/* Max region index + 1 */
>  	__u32	num_irqs;	/* Max IRQ index + 1 */
>  };

Clearly this has only been tested for a single instance of an AER error
event and resume per device.  Are the things you're intending to block
actually blocked for subsequent events?  Note how complete_all() fills
the done field to let all current and future waiters go through and
nowhere is there a call to reinit_completion() to drain that path.
Thanks,

Alex

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#1452937

From	Zhou Jie <zhoujie2011@cn.fujitsu.com>
Date	2016-08-01 04:20 +0200
Message-ID	<s1aZH-8uR-3@gated-at.bofh.it>
In reply to	#1452485

Hi, Alex

On 2016/7/30 1:12, Alex Williamson wrote:
> On Tue, 19 Jul 2016 15:32:43 +0800
> Zhou Jie <zhoujie2011@cn.fujitsu.com> wrote:
>
>> From: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
>>
>> During aer err occurs and resume do following to
>> protect device from being accessed.
>> 1. Make config space read only.
>> 2. Disable INTx/MSI Interrupt.
>> 3. Do nothing for bar regions.
>>
>> Signed-off-by: Zhou Jie <zhoujie2011@cn.fujitsu.com>
>> ---
>>  drivers/vfio/pci/vfio_pci.c         | 30 ++++++++++++++++++++++++++++++
>>  drivers/vfio/pci/vfio_pci_private.h |  2 ++
>>  include/uapi/linux/vfio.h           |  2 ++
>>  3 files changed, 34 insertions(+)
>>
>> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
>> index 2d12b03..dd96b60 100644
>> --- a/drivers/vfio/pci/vfio_pci.c
>> +++ b/drivers/vfio/pci/vfio_pci.c
>> @@ -318,6 +318,7 @@ static int vfio_pci_open(void *device_data)
>>  		return -ENODEV;
>>
>>  	mutex_lock(&driver_lock);
>> +	init_completion(&vdev->aer_error_completion);
>>
>>  	if (!vdev->refcnt) {
>>  		ret = vfio_pci_enable(vdev);
>> @@ -571,6 +572,16 @@ static long vfio_pci_ioctl(void *device_data,
>>  	struct vfio_pci_device *vdev = device_data;
>>  	unsigned long minsz;
>>
>> +	if (vdev->aer_error_in_progress && (cmd == VFIO_DEVICE_SET_IRQS ||
>> +	    cmd == VFIO_DEVICE_RESET || cmd == VFIO_DEVICE_PCI_HOT_RESET)) {
>> +		int ret;
>> +		ret = wait_for_completion_interruptible(
>> +			&vdev->aer_error_completion);
>> +		if (ret) {
>> +			return ret;
>> +		}
>
> No brackets necessary.
>
>> +	}
>> +
>>  	if (cmd == VFIO_DEVICE_GET_INFO) {
>>  		struct vfio_device_info info;
>>
>> @@ -587,6 +598,10 @@ static long vfio_pci_ioctl(void *device_data,
>>  		if (vdev->reset_works)
>>  			info.flags |= VFIO_DEVICE_FLAGS_RESET;
>>
>> +		info.flags |= VFIO_DEVICE_FLAGS_AERPROCESS;
>> +		if (vdev->aer_error_in_progress)
>> +			info.flags |= VFIO_DEVICE_FLAGS_INAERPROCESS;
>> +
>>  		info.num_regions = VFIO_PCI_NUM_REGIONS + vdev->num_regions;
>>  		info.num_irqs = VFIO_PCI_NUM_IRQS;
>>
>> @@ -996,6 +1011,14 @@ static ssize_t vfio_pci_rw(void *device_data, char __user *buf,
>>
>>  	switch (index) {
>>  	case VFIO_PCI_CONFIG_REGION_INDEX:
>> +		if (vdev->aer_error_in_progress && iswrite) {
>> +			int ret;
>> +			ret = wait_for_completion_interruptible(
>> +				&vdev->aer_error_completion);
>> +			if (ret) {
>> +				return ret;
>> +			}
>> +		}
>>  		return vfio_pci_config_rw(vdev, buf, count, ppos, iswrite);
>>
>>  	case VFIO_PCI_ROM_REGION_INDEX:
>> @@ -1226,6 +1249,10 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
>>
>>  	mutex_lock(&vdev->igate);
>>
>> +	vdev->aer_error_in_progress = true;
>> +	vfio_pci_set_irqs_ioctl(vdev, VFIO_IRQ_SET_DATA_NONE |
>> +				VFIO_IRQ_SET_ACTION_TRIGGER,
>> +				vdev->irq_type, 0, 0, NULL);
>>  	if (vdev->err_trigger)
>>  		eventfd_signal(vdev->err_trigger, 1);
>>
>> @@ -1252,6 +1279,9 @@ static void vfio_pci_aer_resume(struct pci_dev *pdev)
>>  	}
>>
>>  	mutex_lock(&vdev->igate);
>> +
>> +	vdev->aer_error_in_progress = false;
>> +	complete_all(&vdev->aer_error_completion);
>>  	if (vdev->resume_trigger)
>>  		eventfd_signal(vdev->resume_trigger, 1);
>>
>> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
>> index 80d4ddd..2f151f5 100644
>> --- a/drivers/vfio/pci/vfio_pci_private.h
>> +++ b/drivers/vfio/pci/vfio_pci_private.h
>> @@ -84,6 +84,8 @@ struct vfio_pci_device {
>>  	bool			has_vga;
>>  	bool			needs_reset;
>>  	bool			nointx;
>> +	bool			aer_error_in_progress;
>> +	struct completion	aer_error_completion;
>>  	struct pci_saved_state	*pci_saved_state;
>>  	int			refcnt;
>>  	struct eventfd_ctx	*err_trigger;
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index 34ab138..276ce50 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -198,6 +198,8 @@ struct vfio_device_info {
>>  #define VFIO_DEVICE_FLAGS_PCI	(1 << 1)	/* vfio-pci device */
>>  #define VFIO_DEVICE_FLAGS_PLATFORM (1 << 2)	/* vfio-platform device */
>>  #define VFIO_DEVICE_FLAGS_AMBA  (1 << 3)	/* vfio-amba device */
>> +#define VFIO_DEVICE_FLAGS_AERPROCESS  (1 << 4)	/* support aer error progress */
>> +#define VFIO_DEVICE_FLAGS_INAERPROCESS  (1 << 5)/* status in aer error progress */
>>  	__u32	num_regions;	/* Max region index + 1 */
>>  	__u32	num_irqs;	/* Max IRQ index + 1 */
>>  };
>
> Clearly this has only been tested for a single instance of an AER error
> event and resume per device.  Are the things you're intending to block
> actually blocked for subsequent events?  Note how complete_all() fills
> the done field to let all current and future waiters go through and
> nowhere is there a call to reinit_completion() to drain that path.
> Thanks,
>
> Alex

Do you mean this condition?

For device 1:
error1 occurs ---- error1 resumes
     error2 occurs ---- error2 resumes
         error3 occurs ---- error3 resumes

In current code, I do complete_all() when error1 resumes.
And this will unblock the device
when error2 and error3 are still be processed.

Sincerely
ZhouJie

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#1453282

From	Alex Williamson <alex.williamson@redhat.com>
Date	2016-08-01 17:40 +0200
Message-ID	<s1ntT-88a-5@gated-at.bofh.it>
In reply to	#1452937

On Mon, 1 Aug 2016 10:14:06 +0800
Zhou Jie <zhoujie2011@cn.fujitsu.com> wrote:

> Hi, Alex
> 
> On 2016/7/30 1:12, Alex Williamson wrote:
> > On Tue, 19 Jul 2016 15:32:43 +0800
> > Zhou Jie <zhoujie2011@cn.fujitsu.com> wrote:
> >  
> >> From: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> >>
> >> During aer err occurs and resume do following to
> >> protect device from being accessed.
> >> 1. Make config space read only.
> >> 2. Disable INTx/MSI Interrupt.
> >> 3. Do nothing for bar regions.
> >>
> >> Signed-off-by: Zhou Jie <zhoujie2011@cn.fujitsu.com>
> >> ---
> >>  drivers/vfio/pci/vfio_pci.c         | 30 ++++++++++++++++++++++++++++++
> >>  drivers/vfio/pci/vfio_pci_private.h |  2 ++
> >>  include/uapi/linux/vfio.h           |  2 ++
> >>  3 files changed, 34 insertions(+)
> >>
> >> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> >> index 2d12b03..dd96b60 100644
> >> --- a/drivers/vfio/pci/vfio_pci.c
> >> +++ b/drivers/vfio/pci/vfio_pci.c
> >> @@ -318,6 +318,7 @@ static int vfio_pci_open(void *device_data)
> >>  		return -ENODEV;
> >>
> >>  	mutex_lock(&driver_lock);
> >> +	init_completion(&vdev->aer_error_completion);
> >>
> >>  	if (!vdev->refcnt) {
> >>  		ret = vfio_pci_enable(vdev);
> >> @@ -571,6 +572,16 @@ static long vfio_pci_ioctl(void *device_data,
> >>  	struct vfio_pci_device *vdev = device_data;
> >>  	unsigned long minsz;
> >>
> >> +	if (vdev->aer_error_in_progress && (cmd == VFIO_DEVICE_SET_IRQS ||
> >> +	    cmd == VFIO_DEVICE_RESET || cmd == VFIO_DEVICE_PCI_HOT_RESET)) {
> >> +		int ret;
> >> +		ret = wait_for_completion_interruptible(
> >> +			&vdev->aer_error_completion);
> >> +		if (ret) {
> >> +			return ret;
> >> +		}  
> >
> > No brackets necessary.
> >  
> >> +	}
> >> +
> >>  	if (cmd == VFIO_DEVICE_GET_INFO) {
> >>  		struct vfio_device_info info;
> >>
> >> @@ -587,6 +598,10 @@ static long vfio_pci_ioctl(void *device_data,
> >>  		if (vdev->reset_works)
> >>  			info.flags |= VFIO_DEVICE_FLAGS_RESET;
> >>
> >> +		info.flags |= VFIO_DEVICE_FLAGS_AERPROCESS;
> >> +		if (vdev->aer_error_in_progress)
> >> +			info.flags |= VFIO_DEVICE_FLAGS_INAERPROCESS;
> >> +
> >>  		info.num_regions = VFIO_PCI_NUM_REGIONS + vdev->num_regions;
> >>  		info.num_irqs = VFIO_PCI_NUM_IRQS;
> >>
> >> @@ -996,6 +1011,14 @@ static ssize_t vfio_pci_rw(void *device_data, char __user *buf,
> >>
> >>  	switch (index) {
> >>  	case VFIO_PCI_CONFIG_REGION_INDEX:
> >> +		if (vdev->aer_error_in_progress && iswrite) {
> >> +			int ret;
> >> +			ret = wait_for_completion_interruptible(
> >> +				&vdev->aer_error_completion);
> >> +			if (ret) {
> >> +				return ret;
> >> +			}
> >> +		}
> >>  		return vfio_pci_config_rw(vdev, buf, count, ppos, iswrite);
> >>
> >>  	case VFIO_PCI_ROM_REGION_INDEX:
> >> @@ -1226,6 +1249,10 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
> >>
> >>  	mutex_lock(&vdev->igate);
> >>
> >> +	vdev->aer_error_in_progress = true;
> >> +	vfio_pci_set_irqs_ioctl(vdev, VFIO_IRQ_SET_DATA_NONE |
> >> +				VFIO_IRQ_SET_ACTION_TRIGGER,
> >> +				vdev->irq_type, 0, 0, NULL);
> >>  	if (vdev->err_trigger)
> >>  		eventfd_signal(vdev->err_trigger, 1);
> >>
> >> @@ -1252,6 +1279,9 @@ static void vfio_pci_aer_resume(struct pci_dev *pdev)
> >>  	}
> >>
> >>  	mutex_lock(&vdev->igate);
> >> +
> >> +	vdev->aer_error_in_progress = false;
> >> +	complete_all(&vdev->aer_error_completion);
> >>  	if (vdev->resume_trigger)
> >>  		eventfd_signal(vdev->resume_trigger, 1);
> >>
> >> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> >> index 80d4ddd..2f151f5 100644
> >> --- a/drivers/vfio/pci/vfio_pci_private.h
> >> +++ b/drivers/vfio/pci/vfio_pci_private.h
> >> @@ -84,6 +84,8 @@ struct vfio_pci_device {
> >>  	bool			has_vga;
> >>  	bool			needs_reset;
> >>  	bool			nointx;
> >> +	bool			aer_error_in_progress;
> >> +	struct completion	aer_error_completion;
> >>  	struct pci_saved_state	*pci_saved_state;
> >>  	int			refcnt;
> >>  	struct eventfd_ctx	*err_trigger;
> >> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> >> index 34ab138..276ce50 100644
> >> --- a/include/uapi/linux/vfio.h
> >> +++ b/include/uapi/linux/vfio.h
> >> @@ -198,6 +198,8 @@ struct vfio_device_info {
> >>  #define VFIO_DEVICE_FLAGS_PCI	(1 << 1)	/* vfio-pci device */
> >>  #define VFIO_DEVICE_FLAGS_PLATFORM (1 << 2)	/* vfio-platform device */
> >>  #define VFIO_DEVICE_FLAGS_AMBA  (1 << 3)	/* vfio-amba device */
> >> +#define VFIO_DEVICE_FLAGS_AERPROCESS  (1 << 4)	/* support aer error progress */
> >> +#define VFIO_DEVICE_FLAGS_INAERPROCESS  (1 << 5)/* status in aer error progress */
> >>  	__u32	num_regions;	/* Max region index + 1 */
> >>  	__u32	num_irqs;	/* Max IRQ index + 1 */
> >>  };  
> >
> > Clearly this has only been tested for a single instance of an AER error
> > event and resume per device.  Are the things you're intending to block
> > actually blocked for subsequent events?  Note how complete_all() fills
> > the done field to let all current and future waiters go through and
> > nowhere is there a call to reinit_completion() to drain that path.
> > Thanks,
> >
> > Alex  
> 
> Do you mean this condition?
> 
> For device 1:
> error1 occurs ---- error1 resumes
>      error2 occurs ---- error2 resumes
>          error3 occurs ---- error3 resumes
> 
> In current code, I do complete_all() when error1 resumes.
> And this will unblock the device
> when error2 and error3 are still be processed.

So walk me through how this works.  On vfio_pci_open() we call
init_completion(), which sets aer_error_completion.done equal to zero
(BTW, a user can open the device file descriptor multiple times, so
there's already a bug here).  Let's assume that an error occurs and the
user stalls a single access on wait_for_completion_interruptible().
The bulk of this function happens here:

static inline long __sched
do_wait_for_common(struct completion *x,
                   long (*action)(long), long timeout, int state)
{
        if (!x->done) {
                DECLARE_WAITQUEUE(wait, current);

                __add_wait_queue_tail_exclusive(&x->wait, &wait);
                do {
                        if (signal_pending_state(state, current)) {
                                timeout = -ERESTARTSYS;
                                break;
                        }
                        __set_current_state(state);
                        spin_unlock_irq(&x->wait.lock);
                        timeout = action(timeout);
                        spin_lock_irq(&x->wait.lock);
                } while (!x->done && timeout);
                __remove_wait_queue(&x->wait, &wait);
                if (!x->done)
                        return timeout;
        }
        x->done--;
        return timeout ?: 1;
}

So it waits within that do{}while loop for a completion, interruption,
or timeout.  Then we have:

void complete_all(struct completion *x)
{
        unsigned long flags;

        spin_lock_irqsave(&x->wait.lock, flags);
        x->done += UINT_MAX/2;
        __wake_up_locked(&x->wait, TASK_NORMAL, 0);
        spin_unlock_irqrestore(&x->wait.lock, flags);
}

So aer_error_completion.done gets incremented to let a couple billion
completion waiters through...  Show me how another call to
wait_for_completion_interruptible() will ever block again within our
lifetime when the actual wait of do_wait_for_common() is only entered
when 'done' count is equal to zero.  This seems to be why
reinit_completion() exists, but it's not used here.  Thanks,

Alex

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#1453530

From	Zhou Jie <zhoujie2011@cn.fujitsu.com>
Date	2016-08-02 03:30 +0200
Message-ID	<s1wGW-5Vm-9@gated-at.bofh.it>
In reply to	#1453282

Hi, Alex

>>> Clearly this has only been tested for a single instance of an AER error
>>> event and resume per device.  Are the things you're intending to block
>>> actually blocked for subsequent events?  Note how complete_all() fills
>>> the done field to let all current and future waiters go through and
>>> nowhere is there a call to reinit_completion() to drain that path.
>>> Thanks,
>>>
>>> Alex
>>
>> Do you mean this condition?
>>
>> For device 1:
>> error1 occurs ---- error1 resumes
>>      error2 occurs ---- error2 resumes
>>          error3 occurs ---- error3 resumes
>>
>> In current code, I do complete_all() when error1 resumes.
>> And this will unblock the device
>> when error2 and error3 are still be processed.
>
> So walk me through how this works.  On vfio_pci_open() we call
> init_completion(), which sets aer_error_completion.done equal to zero
> (BTW, a user can open the device file descriptor multiple times, so
> there's already a bug here).
I will call init_completion() in vfio_pci_probe.

> Let's assume that an error occurs and the
> user stalls a single access on wait_for_completion_interruptible().
> The bulk of this function happens here:
>
> static inline long __sched
> do_wait_for_common(struct completion *x,
>                    long (*action)(long), long timeout, int state)
> {
>         if (!x->done) {
>                 DECLARE_WAITQUEUE(wait, current);
>
>                 __add_wait_queue_tail_exclusive(&x->wait, &wait);
>                 do {
>                         if (signal_pending_state(state, current)) {
>                                 timeout = -ERESTARTSYS;
>                                 break;
>                         }
>                         __set_current_state(state);
>                         spin_unlock_irq(&x->wait.lock);
>                         timeout = action(timeout);
>                         spin_lock_irq(&x->wait.lock);
>                 } while (!x->done && timeout);
>                 __remove_wait_queue(&x->wait, &wait);
>                 if (!x->done)
>                         return timeout;
>         }
>         x->done--;
>         return timeout ?: 1;
> }
>
> So it waits within that do{}while loop for a completion, interruption,
> or timeout.  Then we have:
>
> void complete_all(struct completion *x)
> {
>         unsigned long flags;
>
>         spin_lock_irqsave(&x->wait.lock, flags);
>         x->done += UINT_MAX/2;
>         __wake_up_locked(&x->wait, TASK_NORMAL, 0);
>         spin_unlock_irqrestore(&x->wait.lock, flags);
> }
>
> So aer_error_completion.done gets incremented to let a couple billion
> completion waiters through...  Show me how another call to
> wait_for_completion_interruptible() will ever block again within our
> lifetime when the actual wait of do_wait_for_common() is only entered
> when 'done' count is equal to zero.  This seems to be why
> reinit_completion() exists, but it's not used here.  Thanks,
>
> Alex

I will call reinit_completion() in vfio_pci_aer_err_detected when
an aer error is detected.
Thank you very much.

Sincerely
ZhouJie

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Re: [Qemu-devel] [PATCH v2 2/2] vfio : add aer process

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#1452485 — Re: [Qemu-devel] [PATCH v2 2/2] vfio : add aer process

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