Michael S. Tsirkin
2019-Jul-18 20:45 UTC
[PATCH v5 1/2] mm/balloon_compaction: avoid duplicate page removal
From: Wei Wang <wei.w.wang at intel.com>
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.
This is necessary when it's used from balloon_page_enqueue_list, but
not from balloon_page_enqueue.
Move list_del to balloon_page_enqueue, and update comments accordingly.
Fixes: 418a3ab1e778 (mm/balloon_compaction: List interfaces)
Signed-off-by: Wei Wang <wei.w.wang at intel.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
Note: no need for CC stable since 418a3ab1e778 is new since 5.2
mm/balloon_compaction.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 83a7b614061f..d25664e1857b 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -21,7 +21,6 @@ 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 +46,7 @@ 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++;
}
@@ -128,13 +128,19 @@ struct page *balloon_page_alloc(void)
EXPORT_SYMBOL_GPL(balloon_page_alloc);
/*
- * balloon_page_enqueue - allocates a new page and inserts it into the balloon
- * page list.
+ * balloon_page_enqueue - inserts a new page into the balloon page list.
+ *
* @b_dev_info: balloon device descriptor where we will insert a new page to
* @page: new page to enqueue - allocated using balloon_page_alloc.
*
* Driver must call it to properly enqueue a new allocated balloon page
* before definitively removing it from the guest system.
+ *
+ * Drivers must not call balloon_page_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.
+ *
* This function returns the page address for the recently enqueued page or
* NULL in the case we fail to allocate a new page this turn.
*/
--
MST
Lots of comments bitrotted. Fix them up.
Fixes: 418a3ab1e778 (mm/balloon_compaction: List interfaces)
Reviewed-by: Wei Wang <wei.w.wang at intel.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
Acked-by: Nadav Amit <namit at vmware.com>
---
mm/balloon_compaction.c | 67 +++++++++++++++++++++++------------------
1 file changed, 37 insertions(+), 30 deletions(-)
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index d25664e1857b..798275a51887 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -32,8 +32,8 @@ static void balloon_page_enqueue_one(struct balloon_dev_info
*b_dev_info,
* @b_dev_info: balloon device descriptor where we will insert a new page to
* @pages: pages to enqueue - allocated using balloon_page_alloc.
*
- * Driver must call it to properly enqueue a balloon pages before definitively
- * removing it from the guest system.
+ * Driver must call this function to properly enqueue balloon pages before
+ * definitively removing them from the guest system.
*
* Return: number of pages that were enqueued.
*/
@@ -63,12 +63,13 @@ EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);
* @n_req_pages: number of requested pages.
*
* Driver must call this function to properly de-allocate a previous enlisted
- * balloon pages before definetively releasing it back to the guest system.
+ * balloon pages before definitively releasing it back to the guest system.
* This function tries to remove @n_req_pages from the ballooned pages and
* return them to the caller in the @pages list.
*
- * Note that this function may fail to dequeue some pages temporarily empty due
- * to compaction isolated pages.
+ * Note that this function may fail to dequeue some pages even if the balloon
+ * isn't empty - since the page list can be temporarily empty due to
compaction
+ * of isolated pages.
*
* Return: number of pages that were added to the @pages list.
*/
@@ -112,12 +113,13 @@ EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);
/*
* balloon_page_alloc - allocates a new page for insertion into the balloon
- * page list.
+ * page list.
*
- * Driver must call it to properly allocate a new enlisted balloon page.
- * Driver must call balloon_page_enqueue before definitively removing it from
- * the guest system. This function returns the page address for the recently
- * allocated page or NULL in the case we fail to allocate a new page this turn.
+ * Driver must call this function to properly allocate a new balloon page.
+ * Driver must call balloon_page_enqueue before definitively removing the page
+ * from the guest system.
+ *
+ * Return: struct page for the allocated page or NULL on allocation failure.
*/
struct page *balloon_page_alloc(void)
{
@@ -130,19 +132,15 @@ EXPORT_SYMBOL_GPL(balloon_page_alloc);
/*
* balloon_page_enqueue - inserts a new page into the balloon page list.
*
- * @b_dev_info: balloon device descriptor where we will insert a new page to
+ * @b_dev_info: balloon device descriptor where we will insert a new page
* @page: new page to enqueue - allocated using balloon_page_alloc.
*
- * Driver must call it to properly enqueue a new allocated balloon page
- * before definitively removing it from the guest system.
+ * Drivers must call this function to properly enqueue a new allocated balloon
+ * page before definitively removing the page from the guest system.
*
- * Drivers must not call balloon_page_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.
- *
- * This function returns the page address for the recently enqueued page or
- * NULL in the case we fail to allocate a new page this turn.
+ * Drivers must not call balloon_page_enqueue on pages that have been pushed to
+ * a list with balloon_page_push before removing them with balloon_page_pop. To
+ * enqueue a list of pages, use balloon_page_list_enqueue instead.
*/
void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
struct page *page)
@@ -157,14 +155,23 @@ EXPORT_SYMBOL_GPL(balloon_page_enqueue);
/*
* balloon_page_dequeue - removes a page from balloon's page list and
returns
- * the its address to allow the driver release the page.
+ * its address to allow the driver to release the page.
* @b_dev_info: balloon device decriptor where we will grab a page from.
*
- * Driver must call it to properly de-allocate a previous enlisted balloon page
- * before definetively releasing it back to the guest system.
- * This function returns the page address for the recently dequeued page or
- * NULL in the case we find balloon's page list temporarily empty due to
- * compaction isolated pages.
+ * Driver must call this function to properly dequeue a previously enqueued
page
+ * before definitively releasing it back to the guest system.
+ *
+ * Caller must perform its own accounting to ensure that this
+ * function is called only if some pages are actually enqueued.
+ *
+ * Note that this function may fail to dequeue some pages even if there are
+ * some enqueued pages - since the page list can be temporarily empty due to
+ * the compaction of isolated pages.
+ *
+ * TODO: remove the caller accounting requirements, and allow caller to wait
+ * until all pages can be dequeued.
+ *
+ * Return: struct page for the dequeued page, or NULL if no page was dequeued.
*/
struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
{
@@ -177,9 +184,9 @@ struct page *balloon_page_dequeue(struct balloon_dev_info
*b_dev_info)
if (n_pages != 1) {
/*
* If we are unable to dequeue a balloon page because the page
- * list is empty and there is no isolated pages, then something
+ * list is empty and there are no isolated pages, then something
* went out of track and some balloon pages are lost.
- * BUG() here, otherwise the balloon driver may get stuck into
+ * BUG() here, otherwise the balloon driver may get stuck in
* an infinite loop while attempting to release all its pages.
*/
spin_lock_irqsave(&b_dev_info->pages_lock, flags);
@@ -230,8 +237,8 @@ int balloon_page_migrate(struct address_space *mapping,
/*
* We can not easily support the no copy case here so ignore it as it
- * is unlikely to be use with ballon pages. See include/linux/hmm.h for
- * user of the MIGRATE_SYNC_NO_COPY mode.
+ * is unlikely to be used with balloon pages. See include/linux/hmm.h
+ * for a user of the MIGRATE_SYNC_NO_COPY mode.
*/
if (mode == MIGRATE_SYNC_NO_COPY)
return -EINVAL;
--
MST