From c7cdff0e864713a089d7cb3a2b1136ba9a54881a Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Fri, 13 Oct 2017 16:11:48 +0300 Subject: virtio_balloon: fix deadlock on OOM 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 Cc: Michal Hocko Cc: Wei Wang Signed-off-by: Michael S. Tsirkin --- drivers/virtio/virtio_balloon.c | 24 +++++++++++++++++++----- 1 file changed, 19 insertions(+), 5 deletions(-) (limited to 'drivers/virtio/virtio_balloon.c') diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index f0b3a0b9d42f..7960746f7597 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -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, -- cgit v1.2.3