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.
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 <[email protected]>
---
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. */
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
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 <[email protected]>
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
On 07/18/2019 12:31 PM, Michael S. Tsirkin wrote:
> 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 <[email protected]>
> 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
Probably, you meant balloon_page_enqueue here.
The description for balloon_page_enqueue also seems incorrect:
"allocates a new page and inserts it into the balloon page list."
This function doesn't do any allocation itself.
Plan to reword it: inserts a new page into the balloon page list."
Best,
Wei
On Thu, Jul 18, 2019 at 02:31:14PM +0800, Wei Wang wrote:
> On 07/18/2019 12:31 PM, Michael S. Tsirkin wrote:
> > 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 <[email protected]>
> > 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
>
> Probably, you meant balloon_page_enqueue here.
yes
> The description for balloon_page_enqueue also seems incorrect:
> "allocates a new page and inserts it into the balloon page list."
> This function doesn't do any allocation itself.
> Plan to reword it: inserts a new page into the balloon page list."
And maybe
" Page must have been allocated with balloon_page_alloc.".
Also
* Driver must call it to properly enqueue a balloon pages before definitively
should be
* Driver must call it to properly enqueue balloon pages before definitively
>
> Best,
> Wei