4.14-stable review patch. If anyone has any objections, please let me know.
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From: Michael S. Tsirkin mst@redhat.com
commit c7cdff0e864713a089d7cb3a2b1136ba9a54881a upstream.
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 Signed-off-by: Sudip Mukherjee sudipm.mukherjee@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/virtio/virtio_balloon.c | 24 +++++++++++++++++++----- include/linux/balloon_compaction.h | 35 ++++++++++++++++++++++++++++++++++- mm/balloon_compaction.c | 28 +++++++++++++++++++++------- 3 files changed, 74 insertions(+), 13 deletions(-)
--- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -143,16 +143,17 @@ static void set_page_pfns(struct virtio_
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 virt 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, --- a/include/linux/balloon_compaction.h +++ b/include/linux/balloon_compaction.h @@ -50,6 +50,7 @@ #include <linux/gfp.h> #include <linux/err.h> #include <linux/fs.h> +#include <linux/list.h>
/* * Balloon device information descriptor. @@ -67,7 +68,9 @@ struct balloon_dev_info { struct inode *inode; };
-extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info); +extern struct page *balloon_page_alloc(void); +extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info, + struct page *page); extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
static inline void balloon_devinfo_init(struct balloon_dev_info *balloon) @@ -193,4 +196,34 @@ static inline gfp_t balloon_mapping_gfp_ }
#endif /* CONFIG_BALLOON_COMPACTION */ + +/* + * balloon_page_push - insert a page into a page list. + * @head : pointer to list + * @page : page to be added + * + * Caller must ensure the page is private and protect the list. + */ +static inline void balloon_page_push(struct list_head *pages, struct page *page) +{ + list_add(&page->lru, pages); +} + +/* + * balloon_page_pop - remove a page from a page list. + * @head : pointer to list + * @page : page to be added + * + * Caller must ensure the page is private and protect the list. + */ +static inline struct page *balloon_page_pop(struct list_head *pages) +{ + struct page *page = list_first_entry_or_null(pages, struct page, lru); + + if (!page) + return NULL; + + list_del(&page->lru); + return page; +} #endif /* _LINUX_BALLOON_COMPACTION_H */ --- a/mm/balloon_compaction.c +++ b/mm/balloon_compaction.c @@ -11,22 +11,37 @@ #include <linux/balloon_compaction.h>
/* + * balloon_page_alloc - allocates a new page for insertion into the balloon + * 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. + */ +struct page *balloon_page_alloc(void) +{ + struct page *page = alloc_page(balloon_mapping_gfp_mask() | + __GFP_NOMEMALLOC | __GFP_NORETRY); + return page; +} +EXPORT_SYMBOL_GPL(balloon_page_alloc); + +/* * balloon_page_enqueue - allocates a new page and inserts it 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 allocate a new enlisted balloon page + * Driver must call it to properly enqueue a new allocated balloon page * before definitively removing it from the guest system. * 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. */ -struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info) +void balloon_page_enqueue(struct balloon_dev_info *b_dev_info, + struct page *page) { unsigned long flags; - struct page *page = alloc_page(balloon_mapping_gfp_mask() | - __GFP_NOMEMALLOC | __GFP_NORETRY); - if (!page) - return NULL;
/* * Block others from accessing the 'page' when we get around to @@ -39,7 +54,6 @@ struct page *balloon_page_enqueue(struct __count_vm_event(BALLOON_INFLATE); spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); unlock_page(page); - return page; } EXPORT_SYMBOL_GPL(balloon_page_enqueue);