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[PATCH] xen-netback: correctly check failed allocation

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  [PATCH] xen-netback: correctly check failed allocation Insu Yun <wuninsu@gmail.com> - 2015-10-15 20:10 +0200
    Re: [PATCH] xen-netback: correctly check failed allocation Wei Liu <wei.liu2@citrix.com> - 2015-10-16 11:10 +0200
      Re: [PATCH] xen-netback: correctly check failed allocation Wei Liu <wei.liu2@citrix.com> - 2015-10-16 11:30 +0200
      Re: [Xen-devel] [PATCH] xen-netback: correctly check failed allocation David Vrabel <david.vrabel@citrix.com> - 2015-10-16 11:50 +0200

#1248052 — [PATCH] xen-netback: correctly check failed allocation

Since vzalloc can be failed in memory pressure,
writes -ENOMEM to xenstore to indicate error.

Signed-off-by: Insu Yun <wuninsu@gmail.com>
---
 drivers/net/xen-netback/xenbus.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index 929a6e7..56ebd82 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -788,6 +788,12 @@ static void connect(struct backend_info *be)
 	/* Use the number of queues requested by the frontend */
 	be->vif->queues = vzalloc(requested_num_queues *
 				  sizeof(struct xenvif_queue));
+	if (!be->vif->queues) {
+		xenbus_dev_fatal(dev, -ENOMEM,
+				 "allocating queues");
+		return;
+	}
+
 	be->vif->num_queues = requested_num_queues;
 	be->vif->stalled_queues = requested_num_queues;
 
-- 
1.9.1

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#1248495

On Thu, Oct 15, 2015 at 02:02:47PM -0400, Insu Yun wrote:
> I changed patch with valid format.
> 
> On Thu, Oct 15, 2015 at 2:02 PM, Insu Yun <wuninsu@gmail.com> wrote:
> 
> > Since vzalloc can be failed in memory pressure,
> > writes -ENOMEM to xenstore to indicate error.
> >
> > Signed-off-by: Insu Yun <wuninsu@gmail.com>
> > ---
> >  drivers/net/xen-netback/xenbus.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/net/xen-netback/xenbus.c
> > b/drivers/net/xen-netback/xenbus.c
> > index 929a6e7..56ebd82 100644
> > --- a/drivers/net/xen-netback/xenbus.c
> > +++ b/drivers/net/xen-netback/xenbus.c
> > @@ -788,6 +788,12 @@ static void connect(struct backend_info *be)
> >         /* Use the number of queues requested by the frontend */
> >         be->vif->queues = vzalloc(requested_num_queues *
> >                                   sizeof(struct xenvif_queue));
> > +       if (!be->vif->queues) {
> > +               xenbus_dev_fatal(dev, -ENOMEM,
> > +                                "allocating queues");
> > +               return;
> >
> 
> I didn't use goto err, because another error handling is not required
> 

It's recommended in kernel coding style to use "goto" style error
handling. I personally prefer that to arbitrary return in function body,
too.

It's not a matter of whether another error handling is required or not,
it's about cleaner code that is easy to reason about and consistent
coding style.

The existing code is not perfect, but that doesn't mean we should follow
bad example.

Wei.

> 
> > +       }
> > +
> >         be->vif->num_queues = requested_num_queues;
> >         be->vif->stalled_queues = requested_num_queues;
> >
> > --
> > 1.9.1
> >
> >
> 
> 
> -- 
> Regards
> Insu Yun
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#1248513

On Fri, Oct 16, 2015 at 10:05:21AM +0100, Wei Liu wrote:
> On Thu, Oct 15, 2015 at 02:02:47PM -0400, Insu Yun wrote:
> > I changed patch with valid format.
> > 
> > On Thu, Oct 15, 2015 at 2:02 PM, Insu Yun <wuninsu@gmail.com> wrote:
> > 
> > > Since vzalloc can be failed in memory pressure,
> > > writes -ENOMEM to xenstore to indicate error.
> > >
> > > Signed-off-by: Insu Yun <wuninsu@gmail.com>
> > > ---
> > >  drivers/net/xen-netback/xenbus.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/drivers/net/xen-netback/xenbus.c
> > > b/drivers/net/xen-netback/xenbus.c
> > > index 929a6e7..56ebd82 100644
> > > --- a/drivers/net/xen-netback/xenbus.c
> > > +++ b/drivers/net/xen-netback/xenbus.c
> > > @@ -788,6 +788,12 @@ static void connect(struct backend_info *be)
> > >         /* Use the number of queues requested by the frontend */
> > >         be->vif->queues = vzalloc(requested_num_queues *
> > >                                   sizeof(struct xenvif_queue));
> > > +       if (!be->vif->queues) {
> > > +               xenbus_dev_fatal(dev, -ENOMEM,
> > > +                                "allocating queues");
> > > +               return;
> > >
> > 
> > I didn't use goto err, because another error handling is not required
> > 
> 
> It's recommended in kernel coding style to use "goto" style error
> handling. I personally prefer that to arbitrary return in function body,
> too.
> 
> It's not a matter of whether another error handling is required or not,
> it's about cleaner code that is easy to reason about and consistent
> coding style.
> 
> The existing code is not perfect, but that doesn't mean we should follow
> bad example.

And to be clear, I don't want to block this patch just because of this
coding style thing.  It's still an improvement and fix a real problem.
So:

Acked-by: Wei Liu <wei.liu2@citrix.com>
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#1248532 — Re: [Xen-devel] [PATCH] xen-netback: correctly check failed allocation

On 16/10/15 10:05, Wei Liu wrote:
> On Thu, Oct 15, 2015 at 02:02:47PM -0400, Insu Yun wrote:
>> I changed patch with valid format.
>>
>> On Thu, Oct 15, 2015 at 2:02 PM, Insu Yun <wuninsu@gmail.com> wrote:
>>
>>> Since vzalloc can be failed in memory pressure,
>>> writes -ENOMEM to xenstore to indicate error.
>>>
>>> Signed-off-by: Insu Yun <wuninsu@gmail.com>
>>> ---
>>>  drivers/net/xen-netback/xenbus.c | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/drivers/net/xen-netback/xenbus.c
>>> b/drivers/net/xen-netback/xenbus.c
>>> index 929a6e7..56ebd82 100644
>>> --- a/drivers/net/xen-netback/xenbus.c
>>> +++ b/drivers/net/xen-netback/xenbus.c
>>> @@ -788,6 +788,12 @@ static void connect(struct backend_info *be)
>>>         /* Use the number of queues requested by the frontend */
>>>         be->vif->queues = vzalloc(requested_num_queues *
>>>                                   sizeof(struct xenvif_queue));
>>> +       if (!be->vif->queues) {
>>> +               xenbus_dev_fatal(dev, -ENOMEM,
>>> +                                "allocating queues");
>>> +               return;
>>>
>>
>> I didn't use goto err, because another error handling is not required
>>
> 
> It's recommended in kernel coding style to use "goto" style error
> handling. I personally prefer that to arbitrary return in function body,
> too.
> 
> It's not a matter of whether another error handling is required or not,
> it's about cleaner code that is easy to reason about and consistent
> coding style.

Using xenbus_dev_fatal(); return; throughout would be consistent and
easy to reason about.

Also, the goto err path should raise a fatal error (instead of
disconnecting).  I also note that failures in the xen_net_read_rate(),
xen_register_watchers() and read_xenbus_vif_flags() are also not handled.

David
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