On Thu, Jul 18, 2019 at 10:23:30AM +0800, Wei Wang wrote:
> Fixes: 418a3ab1e778 (mm/balloon_compaction: List interfaces)
>
> A #GP is reported in the guest when requesting balloon inflation via
> virtio-balloon. The reason is that the virtio-balloon driver has
> removed the page from its internal page list (via balloon_page_pop),
> but balloon_page_enqueue_one also calls "list_del" to do the removal.
I would add here "this is necessary when it's used from
balloon_page_enqueue_list but not when it's called
from balloon_page_enqueue".
> So remove the list_del in balloon_page_enqueue_one, and have the callers
> do the page removal from their own page lists.
>
> Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
Patch is good but comments need some work.
> ---
> mm/balloon_compaction.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
> index 83a7b61..1a5ddc4 100644
> --- a/mm/balloon_compaction.c
> +++ b/mm/balloon_compaction.c
> @@ -11,6 +11,7 @@
> #include <linux/export.h>
> #include <linux/balloon_compaction.h>
>
> +/* Callers ensure that @page has been removed from its original list. */
This comment does not make sense. E.g. balloon_page_enqueue
does nothing to ensure this. And drivers are not supposed
to care how the page lists are managed. Pls drop.
Instead please add the following to balloon_page_enqueue:
Note: drivers must not call balloon_page_list_enqueue on
pages that have been pushed to a list with balloon_page_push
before removing them with balloon_page_pop.
To all pages on a list, use balloon_page_list_enqueue instead.
> static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
> struct page *page)
> {
> @@ -21,7 +22,6 @@ static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
> * memory corruption is possible and we should stop execution.
> */
> BUG_ON(!trylock_page(page));
> - list_del(&page->lru);
> balloon_page_insert(b_dev_info, page);
> unlock_page(page);
> __count_vm_event(BALLOON_INFLATE);
> @@ -47,6 +47,7 @@ size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
>
> spin_lock_irqsave(&b_dev_info->pages_lock, flags);
> list_for_each_entry_safe(page, tmp, pages, lru) {
> + list_del(&page->lru);
> balloon_page_enqueue_one(b_dev_info, page);
> n_pages++;
> }
> --
> 2.7.4
