Re: [PATCH] virtio-rng: complete have_data completion in removing device

2014-09-09 Thread Amos Kong 
On Mon, Sep 08, 2014 at 11:29:51PM +0800, Amos Kong wrote:
 On Wed, Aug 06, 2014 at 01:55:29PM +0530, Amit Shah wrote:
  On (Wed) 06 Aug 2014 [16:05:41], Amos Kong wrote:
   On Wed, Aug 06, 2014 at 01:35:15AM +0800, Amos Kong wrote:
When we try to hot-remove a busy virtio-rng device from QEMU monitor,
the device can't be hot-removed. Because virtio-rng driver hangs at
wait_for_completion_killable().

This patch fixed the hang by completing have_data completion before
unregistering a virtio-rng device.
   
   Hi Amit,
   
   Before applying this patch, it's blocking insider 
   wait_for_completion_killable() 
   Applied this patch, wait_for_completion_killable() returns 0,
   and vi-data_avail becomes 0, then rng_get_date() will return 0.
  
  Thanks for checking this.
  
   Is it expected result?
  

Hi Amit

  I think what will happen is vi-data_avail will be set to whatever it
  was set last.  In case of a previous successful read request, the
  data_avail will be set to whatever number of bytes the host gave.  On
  doing a hot-unplug on the succeeding wait, the value in data_avail
  will be re-used, and the hwrng core will wrongly take some bytes in
  the buffer as input from the host.
  
  So, I think we need to set vi-data_avail = 0; before calling
  wait_event_completion_killable().

I finally understand content, we need to set vi-data_avail to 0
before returning virtio_read(), it might enter wait_event_completion_killable()
when we try to remove the device.

We call complete() in remove_common(), then wait_event_completion_killable()
will exit, but virtio_read() will be re-entered if the device still
isn't unregistered, then re-stuck inside wait_event_completion_killable().

I tested some complex condition (both quick/slow backend), I found
some problem in below two patches.

I will post another fix later. The test result is expected.

1. Hotplug remove virtio-rng0, dd process will exit with an error:
dd: error reading ‘/dev/hwrng’: Operation not permitted
   virtio-rng0 disappear from 'info pci'
 
2. Re-read by dd, hotplug virtio-rng1, dd process exit with same
   error, virtio-rng1 disappear


Thanks, Amos

  
  Amit
 
 In my latest debugging, I found the hang is caused by unexpected reading
 when we started to remove the device.
 
 I have two draft fix, 1) is skip unexpected reading by checking a
 remove flag. 2) is unregistering device at the beginning of
 remove_common(). I think second patch is better if it won't cause
 new problem.
 
 The original patch (complete in remove_common()) is still necessary.
 
 Test results: hotplug issue disappeared (dd process will quit).
 
 
 diff --git a/drivers/char/hw_random/virtio-rng.c
 b/drivers/char/hw_random/virtio-rng.c
 index 2e3139e..028797c 100644
 --- a/drivers/char/hw_random/virtio-rng.c
 +++ b/drivers/char/hw_random/virtio-rng.c
 @@ -35,6 +35,7 @@ struct virtrng_info {
 unsigned int data_avail;
 int index;
 bool busy;
 +bool remove;
 bool hwrng_register_done;
  };
  
 @@ -68,6 +69,9 @@ static int virtio_read(struct hwrng *rng, void *buf,
 size_t size, bool wait)
 int ret;
 struct virtrng_info *vi = (struct virtrng_info *)rng-priv;
  
 +if (vi-remove)
 +   return 0;
 +
 if (!vi-busy) {
 vi-busy = true;
 init_completion(vi-have_data);
 @@ -137,6 +141,8 @@ static void remove_common(struct virtio_device
 *vdev)
  {
 struct virtrng_info *vi = vdev-priv;
  
 +   vi-remove = true;
 +   complete(vi-have_data);
 vdev-config-reset(vdev);
 vi-busy = false;
 if (vi-hwrng_register_done)
 
 
 diff --git a/drivers/char/hw_random/virtio-rng.c
 b/drivers/char/hw_random/virtio-rng.c
 index 2e3139e..9b8c2ce 100644
 --- a/drivers/char/hw_random/virtio-rng.c
 +++ b/drivers/char/hw_random/virtio-rng.c
 @@ -137,10 +137,11 @@ static void remove_common(struct virtio_device
 *vdev)
  {
 struct virtrng_info *vi = vdev-priv;
  
 -   vdev-config-reset(vdev);
 -   vi-busy = false;
 if (vi-hwrng_register_done)
 hwrng_unregister(vi-hwrng);
 +   complete(vi-have_data);
 +   vdev-config-reset(vdev);
 +   vi-busy = false;
 vdev-config-del_vqs(vdev);
 ida_simple_remove(rng_index_ida, vi-index);
 kfree(vi);
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Re: [PATCH] virtio-rng: complete have_data completion in removing device

2014-09-08 Thread Amos Kong 
On Wed, Aug 06, 2014 at 01:55:29PM +0530, Amit Shah wrote:
 On (Wed) 06 Aug 2014 [16:05:41], Amos Kong wrote:
  On Wed, Aug 06, 2014 at 01:35:15AM +0800, Amos Kong wrote:
   When we try to hot-remove a busy virtio-rng device from QEMU monitor,
   the device can't be hot-removed. Because virtio-rng driver hangs at
   wait_for_completion_killable().
   
   This patch fixed the hang by completing have_data completion before
   unregistering a virtio-rng device.
  
  Hi Amit,
  
  Before applying this patch, it's blocking insider 
  wait_for_completion_killable() 
  Applied this patch, wait_for_completion_killable() returns 0,
  and vi-data_avail becomes 0, then rng_get_date() will return 0.
 
 Thanks for checking this.
 
  Is it expected result?
 
 I think what will happen is vi-data_avail will be set to whatever it
 was set last.  In case of a previous successful read request, the
 data_avail will be set to whatever number of bytes the host gave.  On
 doing a hot-unplug on the succeeding wait, the value in data_avail
 will be re-used, and the hwrng core will wrongly take some bytes in
 the buffer as input from the host.
 
 So, I think we need to set vi-data_avail = 0; before calling
 wait_event_completion_killable().
 
   Amit

In my latest debugging, I found the hang is caused by unexpected reading
when we started to remove the device.

I have two draft fix, 1) is skip unexpected reading by checking a
remove flag. 2) is unregistering device at the beginning of
remove_common(). I think second patch is better if it won't cause
new problem.

The original patch (complete in remove_common()) is still necessary.

Test results: hotplug issue disappeared (dd process will quit).


diff --git a/drivers/char/hw_random/virtio-rng.c
b/drivers/char/hw_random/virtio-rng.c
index 2e3139e..028797c 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -35,6 +35,7 @@ struct virtrng_info {
unsigned int data_avail;
int index;
bool busy;
+bool remove;
bool hwrng_register_done;
 };
 
@@ -68,6 +69,9 @@ static int virtio_read(struct hwrng *rng, void *buf,
size_t size, bool wait)
int ret;
struct virtrng_info *vi = (struct virtrng_info *)rng-priv;
 
+if (vi-remove)
+   return 0;
+
if (!vi-busy) {
vi-busy = true;
init_completion(vi-have_data);
@@ -137,6 +141,8 @@ static void remove_common(struct virtio_device
*vdev)
 {
struct virtrng_info *vi = vdev-priv;
 
+   vi-remove = true;
+   complete(vi-have_data);
vdev-config-reset(vdev);
vi-busy = false;
if (vi-hwrng_register_done)


diff --git a/drivers/char/hw_random/virtio-rng.c
b/drivers/char/hw_random/virtio-rng.c
index 2e3139e..9b8c2ce 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -137,10 +137,11 @@ static void remove_common(struct virtio_device
*vdev)
 {
struct virtrng_info *vi = vdev-priv;
 
-   vdev-config-reset(vdev);
-   vi-busy = false;
if (vi-hwrng_register_done)
hwrng_unregister(vi-hwrng);
+   complete(vi-have_data);
+   vdev-config-reset(vdev);
+   vi-busy = false;
vdev-config-del_vqs(vdev);
ida_simple_remove(rng_index_ida, vi-index);
kfree(vi);

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Re: [PATCH] virtio-rng: complete have_data completion in removing device

2014-08-06 Thread Amos Kong 
On Wed, Aug 06, 2014 at 01:35:15AM +0800, Amos Kong wrote:
 When we try to hot-remove a busy virtio-rng device from QEMU monitor,
 the device can't be hot-removed. Because virtio-rng driver hangs at
 wait_for_completion_killable().
 
 This patch fixed the hang by completing have_data completion before
 unregistering a virtio-rng device.

Hi Amit,

Before applying this patch, it's blocking insider 
wait_for_completion_killable() 
Applied this patch, wait_for_completion_killable() returns 0,
and vi-data_avail becomes 0, then rng_get_date() will return 0.

Is it expected result?

 
 Signed-off-by: Amos Kong ak...@redhat.com
 Cc: sta...@vger.kernel.org
 ---
  drivers/char/hw_random/virtio-rng.c | 1 +
  1 file changed, 1 insertion(+)
 
 diff --git a/drivers/char/hw_random/virtio-rng.c 
 b/drivers/char/hw_random/virtio-rng.c
 index 0027137..416b15c 100644
 --- a/drivers/char/hw_random/virtio-rng.c
 +++ b/drivers/char/hw_random/virtio-rng.c
 @@ -137,6 +137,7 @@ static void remove_common(struct virtio_device *vdev)
   struct virtrng_info *vi = vdev-priv;
  
   vdev-config-reset(vdev);
 + complete(vi-have_data);
   vi-busy = false;
   if (vi-hwrng_register_done)
   hwrng_unregister(vi-hwrng);
 -- 
 1.9.3
 
 ___
 Virtualization mailing list
 virtualizat...@lists.linux-foundation.org
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Re: [PATCH] virtio-rng: complete have_data completion in removing device

2014-08-06 Thread Amit Shah 
On (Wed) 06 Aug 2014 [16:05:41], Amos Kong wrote:
 On Wed, Aug 06, 2014 at 01:35:15AM +0800, Amos Kong wrote:
  When we try to hot-remove a busy virtio-rng device from QEMU monitor,
  the device can't be hot-removed. Because virtio-rng driver hangs at
  wait_for_completion_killable().
  
  This patch fixed the hang by completing have_data completion before
  unregistering a virtio-rng device.
 
 Hi Amit,
 
 Before applying this patch, it's blocking insider 
 wait_for_completion_killable() 
 Applied this patch, wait_for_completion_killable() returns 0,
 and vi-data_avail becomes 0, then rng_get_date() will return 0.

Thanks for checking this.

 Is it expected result?

I think what will happen is vi-data_avail will be set to whatever it
was set last.  In case of a previous successful read request, the
data_avail will be set to whatever number of bytes the host gave.  On
doing a hot-unplug on the succeeding wait, the value in data_avail
will be re-used, and the hwrng core will wrongly take some bytes in
the buffer as input from the host.

So, I think we need to set vi-data_avail = 0; before calling
wait_event_completion_killable().

Amit
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