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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

35
include/linux/balloon_compaction.h
View file

@ -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 */