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 --- include/linux/balloon_compaction.h | 35 ++++++++++++++++++++++++++++++++++- 1 file changed, 34 insertions(+), 1 deletion(-) (limited to 'include/linux/balloon_compaction.h') diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h index fbbe6da40fed..53051f3d8f25 100644 --- a/include/linux/balloon_compaction.h +++ b/include/linux/balloon_compaction.h @@ -50,6 +50,7 @@ #include #include #include +#include /* * 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 */ -- cgit v1.2.3