| Message ID | 1563416610-11045-1-git-send-email-wei.w.wang@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v1] mm/balloon_compaction: avoid duplicate page removal | expand |
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@intel.com> 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 <wei.w.wang@intel.com> > 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 <wei.w.wang@intel.com> > > 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
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++; }
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 <wei.w.wang@intel.com> --- mm/balloon_compaction.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)