vhost-user-input: use free(elem) instead of g_free(elem)

[PATCH] vhost-user-input: use free(elem) instead of g_free(elem)

Posted by Stefan Hajnoczi 4 years, 5 months ago

The virtqueue element returned by vu_queue_pop() is allocated using
malloc(3) by virtqueue_alloc_element().  Use the matching free(3)
function instead of glib's g_free().

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 contrib/vhost-user-input/main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/contrib/vhost-user-input/main.c b/contrib/vhost-user-input/main.c
index 449fd2171a..ef4b7769f2 100644
--- a/contrib/vhost-user-input/main.c
+++ b/contrib/vhost-user-input/main.c
@@ -77,7 +77,7 @@ static void vi_input_send(VuInput *vi, struct virtio_input_event *event)
         len = iov_from_buf(elem->in_sg, elem->in_num,
                            0, &vi->queue[i].event, sizeof(virtio_input_event));
         vu_queue_push(dev, vq, elem, len);
-        g_free(elem);
+        free(elem);
     }
 
     vu_queue_notify(&vi->dev.parent, vq);
@@ -153,7 +153,7 @@ static void vi_handle_sts(VuDev *dev, int qidx)
                          0, &event, sizeof(event));
         vi_handle_status(vi, &event);
         vu_queue_push(dev, vq, elem, len);
-        g_free(elem);
+        free(elem);
     }
 
     vu_queue_notify(&vi->dev.parent, vq);
-- 
2.23.0

Re: [PATCH] vhost-user-input: use free(elem) instead of g_free(elem)

Posted by Marc-André Lureau 4 years, 5 months ago

On Tue, Nov 19, 2019 at 3:16 PM Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> The virtqueue element returned by vu_queue_pop() is allocated using
> malloc(3) by virtqueue_alloc_element().  Use the matching free(3)
> function instead of glib's g_free().
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

> ---
>  contrib/vhost-user-input/main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/contrib/vhost-user-input/main.c b/contrib/vhost-user-input/main.c
> index 449fd2171a..ef4b7769f2 100644
> --- a/contrib/vhost-user-input/main.c
> +++ b/contrib/vhost-user-input/main.c
> @@ -77,7 +77,7 @@ static void vi_input_send(VuInput *vi, struct virtio_input_event *event)
>          len = iov_from_buf(elem->in_sg, elem->in_num,
>                             0, &vi->queue[i].event, sizeof(virtio_input_event));
>          vu_queue_push(dev, vq, elem, len);
> -        g_free(elem);
> +        free(elem);
>      }
>
>      vu_queue_notify(&vi->dev.parent, vq);
> @@ -153,7 +153,7 @@ static void vi_handle_sts(VuDev *dev, int qidx)
>                           0, &event, sizeof(event));
>          vi_handle_status(vi, &event);
>          vu_queue_push(dev, vq, elem, len);
> -        g_free(elem);
> +        free(elem);
>      }
>
>      vu_queue_notify(&vi->dev.parent, vq);
> --
> 2.23.0
>
>


-- 
Marc-André Lureau

Re: [PATCH] vhost-user-input: use free(elem) instead of g_free(elem)

Posted by Philippe Mathieu-Daudé 4 years, 5 months ago

On 11/19/19 12:16 PM, Stefan Hajnoczi wrote:
> The virtqueue element returned by vu_queue_pop() is allocated using
> malloc(3) by virtqueue_alloc_element().  Use the matching free(3)
> function instead of glib's g_free().
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Fixes: 06914c97d3a ?
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> ---
>   contrib/vhost-user-input/main.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/contrib/vhost-user-input/main.c b/contrib/vhost-user-input/main.c
> index 449fd2171a..ef4b7769f2 100644
> --- a/contrib/vhost-user-input/main.c
> +++ b/contrib/vhost-user-input/main.c
> @@ -77,7 +77,7 @@ static void vi_input_send(VuInput *vi, struct virtio_input_event *event)
>           len = iov_from_buf(elem->in_sg, elem->in_num,
>                              0, &vi->queue[i].event, sizeof(virtio_input_event));
>           vu_queue_push(dev, vq, elem, len);
> -        g_free(elem);
> +        free(elem);
>       }
>   
>       vu_queue_notify(&vi->dev.parent, vq);
> @@ -153,7 +153,7 @@ static void vi_handle_sts(VuDev *dev, int qidx)
>                            0, &event, sizeof(event));
>           vi_handle_status(vi, &event);
>           vu_queue_push(dev, vq, elem, len);
> -        g_free(elem);
> +        free(elem);
>       }
>   
>       vu_queue_notify(&vi->dev.parent, vq);
>

Re: [PATCH] vhost-user-input: use free(elem) instead of g_free(elem)

Posted by Stefan Hajnoczi 4 years, 5 months ago

On Wed, Nov 20, 2019 at 10:37:35AM +0100, Philippe Mathieu-Daudé wrote:
> On 11/19/19 12:16 PM, Stefan Hajnoczi wrote:
> > The virtqueue element returned by vu_queue_pop() is allocated using
> > malloc(3) by virtqueue_alloc_element().  Use the matching free(3)
> > function instead of glib's g_free().
> > 
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> 
> Fixes: 06914c97d3a ?

Good idea, I should have included that.

Stefan

Re: [PATCH] vhost-user-input: use free(elem) instead of g_free(elem)

Posted by Michael S. Tsirkin 4 years, 5 months ago

On Wed, Nov 20, 2019 at 11:41:32AM +0000, Stefan Hajnoczi wrote:
> On Wed, Nov 20, 2019 at 10:37:35AM +0100, Philippe Mathieu-Daudé wrote:
> > On 11/19/19 12:16 PM, Stefan Hajnoczi wrote:
> > > The virtqueue element returned by vu_queue_pop() is allocated using
> > > malloc(3) by virtqueue_alloc_element().  Use the matching free(3)
> > > function instead of glib's g_free().
> > > 
> > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > 
> > Fixes: 06914c97d3a ?
> 
> Good idea, I should have included that.
> 
> Stefan

I'd prefer keeping the Fixes tag to bugfixes as opposed to cleanups.
I.e. it should be a reasonable heuristic for people asking "do I need
this patch" to be able to answer based on whether they have the
linked patch.

-- 
MST

Re: [PATCH] vhost-user-input: use free(elem) instead of g_free(elem)

Posted by Daniel P. Berrangé 4 years, 5 months ago

On Tue, Nov 19, 2019 at 11:16:26AM +0000, Stefan Hajnoczi wrote:
> The virtqueue element returned by vu_queue_pop() is allocated using
> malloc(3) by virtqueue_alloc_element().  Use the matching free(3)
> function instead of glib's g_free().

Just as an FYI, since glib 2.46  g_malloc is hardcoded to use the
system allocator, so it is now guaranteed that g_malloc/malloc
and g_free/free are safely interchangable. I recently got this
clarified in the glib docs:

  https://gitlab.gnome.org/GNOME/glib/merge_requests/1099//diffs

QEMU mandates 2.48 so we are now safe in that regard

For readability/sanity sake I'd still suggest matching functions
but it is not a functional danger any more. Even when it was a
risk, that risk only arose if you called GLib's API for installing
a custom allocator callback which QEMU never did, so it was always
a non-issue.

Where this is most helpful is in exchanging allocated data with
3rd party libraries that don't use glib. We no longer have to
worry about dup'ing memory going in/out libraries not using
glib's allocators.

> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  contrib/vhost-user-input/main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/contrib/vhost-user-input/main.c b/contrib/vhost-user-input/main.c
> index 449fd2171a..ef4b7769f2 100644
> --- a/contrib/vhost-user-input/main.c
> +++ b/contrib/vhost-user-input/main.c
> @@ -77,7 +77,7 @@ static void vi_input_send(VuInput *vi, struct virtio_input_event *event)
>          len = iov_from_buf(elem->in_sg, elem->in_num,
>                             0, &vi->queue[i].event, sizeof(virtio_input_event));
>          vu_queue_push(dev, vq, elem, len);
> -        g_free(elem);
> +        free(elem);
>      }
>  
>      vu_queue_notify(&vi->dev.parent, vq);
> @@ -153,7 +153,7 @@ static void vi_handle_sts(VuDev *dev, int qidx)
>                           0, &event, sizeof(event));
>          vi_handle_status(vi, &event);
>          vu_queue_push(dev, vq, elem, len);
> -        g_free(elem);
> +        free(elem);
>      }
>  
>      vu_queue_notify(&vi->dev.parent, vq);
> -- 
> 2.23.0
> 
> 

Regards,
Daniel
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Re: [PATCH] vhost-user-input: use free(elem) instead of g_free(elem)

Posted by Stefan Hajnoczi 4 years, 5 months ago

On Wed, Nov 20, 2019 at 11:48:56AM +0000, Daniel P. Berrangé wrote:
> On Tue, Nov 19, 2019 at 11:16:26AM +0000, Stefan Hajnoczi wrote:
> > The virtqueue element returned by vu_queue_pop() is allocated using
> > malloc(3) by virtqueue_alloc_element().  Use the matching free(3)
> > function instead of glib's g_free().
> 
> Just as an FYI, since glib 2.46  g_malloc is hardcoded to use the
> system allocator, so it is now guaranteed that g_malloc/malloc
> and g_free/free are safely interchangable. I recently got this
> clarified in the glib docs:
> 
>   https://gitlab.gnome.org/GNOME/glib/merge_requests/1099//diffs
> 
> QEMU mandates 2.48 so we are now safe in that regard
> 
> For readability/sanity sake I'd still suggest matching functions
> but it is not a functional danger any more. Even when it was a
> risk, that risk only arose if you called GLib's API for installing
> a custom allocator callback which QEMU never did, so it was always
> a non-issue.

You are right, although QEMU did use g_mem_set_vtable().  The custom
functions still used malloc() underneath though so it would be safe
anyway:

  commit 98cf48f60aa4999f5b2808569a193a401a390e6a
  Author: Paolo Bonzini <pbonzini@redhat.com>
  Date:   Wed Sep 16 17:38:44 2015 +0200

      trace: remove malloc tracing