Commit 7f42eada authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by Greg Kroah-Hartman

virtio_balloon: fix deadlock on OOM

commit c7cdff0e 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: default avatarTetsuo 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: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarSudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 251bc1f4
......@@ -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,
......
......@@ -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_mask(void)
}
#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 */
......@@ -10,23 +10,38 @@
#include <linux/export.h>
#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 balloon_dev_info *b_dev_info)
__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);
......
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