The balloon_lock was used to synchronize the access demand to elements
of struct virtio_balloon and its queue operations (please see commit
e22504296d). This prevents the concurrent run of the leak_balloon and
fill_balloon functions, thereby resulting in a deadlock issue on OOM:
fill_balloon: take balloon_lock and wait for OOM to get some memory;
oom_notify: release some inflated memory via leak_balloon();
leak_balloon: wait for balloon_lock to be released by fill_balloon.
This patch breaks the lock into two fine-grained inflate_lock and
deflate_lock, and eliminates the unnecessary use of the shared data
(i.e. vb->pnfs, vb->num_pfns). This enables leak_balloon and
fill_balloon to run concurrently and solves the deadlock issue.
Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
---
drivers/virtio/virtio_balloon.c | 102 +++++++++++++++++++++-------------------
1 file changed, 53 insertions(+), 49 deletions(-)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index f0b3a0b..1ecd15a 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -67,7 +67,7 @@ struct virtio_balloon {
wait_queue_head_t acked;
/* Number of balloon pages we've told the Host we're not using. */
- unsigned int num_pages;
+ atomic64_t num_pages;
/*
* The pages we've told the Host we're not using are enqueued
* at vb_dev_info->pages list.
@@ -76,12 +76,9 @@ struct virtio_balloon {
*/
struct balloon_dev_info vb_dev_info;
- /* Synchronize access/update to this struct virtio_balloon elements */
- struct mutex balloon_lock;
-
- /* The array of pfns we tell the Host about. */
- unsigned int num_pfns;
- __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
+ /* Synchronize access to inflate_vq and deflate_vq respectively */
+ struct mutex inflate_lock;
+ struct mutex deflate_lock;
/* Memory statistics */
struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
@@ -111,12 +108,13 @@ static void balloon_ack(struct virtqueue *vq)
wake_up(&vb->acked);
}
-static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
+static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq,
+ __virtio32 pfns[], unsigned int num_pfns)
{
struct scatterlist sg;
unsigned int len;
- sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
+ sg_init_one(&sg, pfns, sizeof(pfns[0]) * num_pfns);
/* We should always be able to add one buffer to an empty queue. */
virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
@@ -144,14 +142,14 @@ static void set_page_pfns(struct virtio_balloon *vb,
static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
{
struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
- unsigned num_allocated_pages;
+ unsigned int num_pfns;
+ __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
/* We can only do one array worth at a time. */
- num = min(num, ARRAY_SIZE(vb->pfns));
+ num = min_t(size_t, num, VIRTIO_BALLOON_ARRAY_PFNS_MAX);
- mutex_lock(&vb->balloon_lock);
- for (vb->num_pfns = 0; vb->num_pfns < num;
- vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
+ for (num_pfns = 0; num_pfns < num;
+ num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
struct page *page = balloon_page_enqueue(vb_dev_info);
if (!page) {
@@ -162,20 +160,20 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
msleep(200);
break;
}
- set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
- vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
+ set_page_pfns(vb, pfns + num_pfns, page);
if (!virtio_has_feature(vb->vdev,
VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
adjust_managed_page_count(page, -1);
}
- num_allocated_pages = vb->num_pfns;
+ mutex_lock(&vb->inflate_lock);
/* Did we get any? */
- if (vb->num_pfns != 0)
- tell_host(vb, vb->inflate_vq);
- mutex_unlock(&vb->balloon_lock);
+ if (num_pfns != 0)
+ tell_host(vb, vb->inflate_vq, pfns, num_pfns);
+ mutex_unlock(&vb->inflate_lock);
+ atomic64_add(num_pfns, &vb->num_pages);
- return num_allocated_pages;
+ return num_pfns;
}
static void release_pages_balloon(struct virtio_balloon *vb,
@@ -194,38 +192,39 @@ static void release_pages_balloon(struct virtio_balloon *vb,
static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
{
- unsigned num_freed_pages;
struct page *page;
struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
LIST_HEAD(pages);
+ unsigned int num_pfns;
+ __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
/* We can only do one array worth at a time. */
- num = min(num, ARRAY_SIZE(vb->pfns));
+ num = min_t(size_t, num, VIRTIO_BALLOON_ARRAY_PFNS_MAX);
- mutex_lock(&vb->balloon_lock);
/* We can't release more pages than taken */
- num = min(num, (size_t)vb->num_pages);
- for (vb->num_pfns = 0; vb->num_pfns < num;
- vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
+ num = min_t(size_t, num, atomic64_read(&vb->num_pages));
+ for (num_pfns = 0; num_pfns < num;
+ num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
page = balloon_page_dequeue(vb_dev_info);
if (!page)
break;
- set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
+ set_page_pfns(vb, pfns + num_pfns, page);
list_add(&page->lru, &pages);
- vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
}
- num_freed_pages = vb->num_pfns;
/*
* Note that if
* virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
* is true, we *have* to do it in this order
*/
- if (vb->num_pfns != 0)
- tell_host(vb, vb->deflate_vq);
+ mutex_lock(&vb->deflate_lock);
+ if (num_pfns != 0)
+ tell_host(vb, vb->deflate_vq, pfns, num_pfns);
+ mutex_unlock(&vb->deflate_lock);
release_pages_balloon(vb, &pages);
- mutex_unlock(&vb->balloon_lock);
- return num_freed_pages;
+ atomic64_sub(num_pfns, &vb->num_pages);
+
+ return num_pfns;
}
static inline void update_stat(struct virtio_balloon *vb, int idx,
@@ -327,12 +326,12 @@ static inline s64 towards_target(struct virtio_balloon *vb)
num_pages = le32_to_cpu((__force __le32)num_pages);
target = num_pages;
- return target - vb->num_pages;
+ return target - atomic64_read(&vb->num_pages);
}
static void update_balloon_size(struct virtio_balloon *vb)
{
- u32 actual = vb->num_pages;
+ u32 actual = atomic64_read(&vb->num_pages);
/* Legacy balloon config space is LE, unlike all other devices. */
if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
@@ -465,6 +464,7 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
struct virtio_balloon *vb = container_of(vb_dev_info,
struct virtio_balloon, vb_dev_info);
unsigned long flags;
+ __virtio32 pfns[VIRTIO_BALLOON_PAGES_PER_PAGE];
/*
* In order to avoid lock contention while migrating pages concurrently
@@ -474,8 +474,12 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
* recursion in the case it ends up triggering memory compaction
* while it is attempting to inflate the ballon.
*/
- if (!mutex_trylock(&vb->balloon_lock))
+ if (!mutex_trylock(&vb->inflate_lock))
+ return -EAGAIN;
+ if (!mutex_trylock(&vb->deflate_lock)) {
+ mutex_unlock(&vb->inflate_lock);
return -EAGAIN;
+ }
get_page(newpage); /* balloon reference */
@@ -485,17 +489,16 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
vb_dev_info->isolated_pages--;
__count_vm_event(BALLOON_MIGRATE);
spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
- vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
- set_page_pfns(vb, vb->pfns, newpage);
- tell_host(vb, vb->inflate_vq);
+
+ set_page_pfns(vb, pfns, newpage);
+ tell_host(vb, vb->inflate_vq, pfns, VIRTIO_BALLOON_PAGES_PER_PAGE);
+ mutex_unlock(&vb->inflate_lock);
/* balloon's page migration 2nd step -- deflate "page" */
balloon_page_delete(page);
- vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
- set_page_pfns(vb, vb->pfns, page);
- tell_host(vb, vb->deflate_vq);
-
- mutex_unlock(&vb->balloon_lock);
+ set_page_pfns(vb, pfns, page);
+ tell_host(vb, vb->deflate_vq, pfns, VIRTIO_BALLOON_PAGES_PER_PAGE);
+ mutex_unlock(&vb->deflate_lock);
put_page(page); /* balloon reference */
@@ -542,8 +545,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
spin_lock_init(&vb->stop_update_lock);
vb->stop_update = false;
- vb->num_pages = 0;
- mutex_init(&vb->balloon_lock);
+ atomic64_set(&vb->num_pages, 0);
+ mutex_init(&vb->inflate_lock);
+ mutex_init(&vb->deflate_lock);
init_waitqueue_head(&vb->acked);
vb->vdev = vdev;
@@ -596,8 +600,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
static void remove_common(struct virtio_balloon *vb)
{
/* There might be pages left in the balloon: free them. */
- while (vb->num_pages)
- leak_balloon(vb, vb->num_pages);
+ while (atomic64_read(&vb->num_pages))
+ leak_balloon(vb, atomic64_read(&vb->num_pages));
update_balloon_size(vb);
/* Now we reset the device so we can clean up the queues. */
--
2.7.4
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