On Tue, Dec 18, 2012 at 06:17:29PM -0200, Luiz Capitulino wrote:
> Today, the balloon_lock mutex is taken and released by fill_balloon()
> and leak_balloon() when both functions are entered and when they
> return.
>
> This commit moves the locking to the caller instead, which is
> the balloon() thread. The balloon thread is the sole caller of those
> functions today.
>
> The reason for this move is that the next commit will introduce
> a shrinker callback for the balloon driver, which will also call
> leak_balloon() but will require different locking semantics.
>
> Signed-off-by: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
> ---
> drivers/virtio/virtio_balloon.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 2a70558..877e695 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -133,7 +133,6 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num)
> /* We can only do one array worth at a time. */
> num = min(num, ARRAY_SIZE(vb->pfns));
>
> - mutex_lock(&vb->balloon_lock);
> for (vb->num_pfns = 0; vb->num_pfns < num;
> vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> struct page *page = balloon_page_enqueue(vb_dev_info);
> @@ -155,7 +154,6 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num)
> /* Did we get any? */
> if (vb->num_pfns != 0)
> tell_host(vb, vb->inflate_vq);
> - mutex_unlock(&vb->balloon_lock);
> }
>
Since you're removing the locking scheme from within this function, I think it
would be a good idea introduce a comment stating its caller must held the mutex
vb->balloon_lock.
> static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
> @@ -177,7 +175,6 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
> /* We can only do one array worth at a time. */
> num = min(num, ARRAY_SIZE(vb->pfns));
>
> - mutex_lock(&vb->balloon_lock);
> for (vb->num_pfns = 0; vb->num_pfns < num;
> vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> page = balloon_page_dequeue(vb_dev_info);
> @@ -193,7 +190,6 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
> * is true, we *have* to do it in this order
> */
> tell_host(vb, vb->deflate_vq);
> - mutex_unlock(&vb->balloon_lock);
> release_pages_by_pfn(vb->pfns, vb->num_pfns);
> }
>
ditto
> @@ -306,11 +302,13 @@ static int balloon(void *_vballoon)
> || freezing(current));
> if (vb->need_stats_update)
> stats_handle_request(vb);
> + mutex_lock(&vb->balloon_lock);
> if (diff > 0)
> fill_balloon(vb, diff);
> else if (diff < 0)
> leak_balloon(vb, -diff);
> update_balloon_size(vb);
> + mutex_unlock(&vb->balloon_lock);
> }
> return 0;
> }
Just a nitpick:
As leak_balloon() is also called at remove_common(), you'll need to introduce the
mutex there, similarly.
Thanks for move this forward.
Cheers!
-- Rafael
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