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virtio_balloon: fix deadlock on OOM

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fill_balloon doing memory allocations under balloon_lock
can cause a deadlock when leak_balloon is called from
virtballoon_oom_notify and tries to take same lock.

To fix, split page allocation and enqueue and do allocations outside the lock.

Here's a detailed analysis of the deadlock by Tetsuo Handa:

In leak_balloon(), mutex_lock(&vb->balloon_lock) is called in order to
serialize against fill_balloon(). But in fill_balloon(),
alloc_page(GFP_HIGHUSER[_MOVABLE] | __GFP_NOMEMALLOC | __GFP_NORETRY) is
called with vb->balloon_lock mutex held. Since GFP_HIGHUSER[_MOVABLE]
implies __GFP_DIRECT_RECLAIM | __GFP_IO | __GFP_FS, despite __GFP_NORETRY
is specified, this allocation attempt might indirectly depend on somebody
else's __GFP_DIRECT_RECLAIM memory allocation. And such indirect
__GFP_DIRECT_RECLAIM memory allocation might call leak_balloon() via
virtballoon_oom_notify() via blocking_notifier_call_chain() callback via
out_of_memory() when it reached __alloc_pages_may_oom() and held oom_lock
mutex. Since vb->balloon_lock mutex is already held by fill_balloon(), it
will cause OOM lockup.

  Thread1                                       Thread2
    fill_balloon()
      takes a balloon_lock
      balloon_page_enqueue()
        alloc_page(GFP_HIGHUSER_MOVABLE)
          direct reclaim (__GFP_FS context)       takes a fs lock
            waits for that fs lock                  alloc_page(GFP_NOFS)
                                                      __alloc_pages_may_oom()
                                                        takes the oom_lock
                                                        out_of_memory()
                                                          blocking_notifier_call_chain()
                                                            leak_balloon()
                                                              tries to take that balloon_lock and deadlocks

Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Michael S. Tsirkin
2017-10-13 16:11:48 +03:00
parent bebc6082da
commit c7cdff0e86
3 changed files with 74 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

24
drivers/virtio/virtio_balloon.c
View File

@@ -143,16 +143,17 @@ 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 num_pfns;
struct page *page;
LIST_HEAD(pages);
/* We can only do one array worth at a time. */
num = min(num, ARRAY_SIZE(vb->pfns));
mutex_lock(&vb->balloon_lock);
for (vb->num_pfns = 0; vb->num_pfns < num;
vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
struct page *page = balloon_page_enqueue(vb_dev_info);
for (num_pfns = 0; num_pfns < num;
num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
struct page *page = balloon_page_alloc();
if (!page) {
dev_info_ratelimited(&vb->vdev->dev,
@@ -162,6 +163,19 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
msleep(200);
break;
}
balloon_page_push(&pages, page);
}
mutex_lock(&vb->balloon_lock);
vb->num_pfns = 0;
while ((page = balloon_page_pop(&pages))) {
balloon_page_enqueue(&vb->vb_dev_info, page);
vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
if (!virtio_has_feature(vb->vdev,