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-rw-r--r--mm/hugetlb.c51
1 files changed, 50 insertions, 1 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ac65bb5e38ac..dd8737a94bec 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -27,6 +27,7 @@
#include <linux/swapops.h>
#include <linux/jhash.h>
#include <linux/numa.h>
+#include <linux/llist.h>
#include <asm/page.h>
#include <asm/pgtable.h>
@@ -1136,7 +1137,7 @@ static inline void ClearPageHugeTemporary(struct page *page)
page[2].mapping = NULL;
}
-void free_huge_page(struct page *page)
+static void __free_huge_page(struct page *page)
{
/*
* Can't pass hstate in here because it is called from the
@@ -1199,6 +1200,54 @@ void free_huge_page(struct page *page)
spin_unlock(&hugetlb_lock);
}
+/*
+ * As free_huge_page() can be called from a non-task context, we have
+ * to defer the actual freeing in a workqueue to prevent potential
+ * hugetlb_lock deadlock.
+ *
+ * free_hpage_workfn() locklessly retrieves the linked list of pages to
+ * be freed and frees them one-by-one. As the page->mapping pointer is
+ * going to be cleared in __free_huge_page() anyway, it is reused as the
+ * llist_node structure of a lockless linked list of huge pages to be freed.
+ */
+static LLIST_HEAD(hpage_freelist);
+
+static void free_hpage_workfn(struct work_struct *work)
+{
+ struct llist_node *node;
+ struct page *page;
+
+ node = llist_del_all(&hpage_freelist);
+
+ while (node) {
+ page = container_of((struct address_space **)node,
+ struct page, mapping);
+ node = node->next;
+ __free_huge_page(page);
+ }
+}
+static DECLARE_WORK(free_hpage_work, free_hpage_workfn);
+
+void free_huge_page(struct page *page)
+{
+ /*
+ * Defer freeing if in non-task context to avoid hugetlb_lock deadlock.
+ */
+ if (!in_task()) {
+ /*
+ * Only call schedule_work() if hpage_freelist is previously
+ * empty. Otherwise, schedule_work() had been called but the
+ * workfn hasn't retrieved the list yet.
+ */
+ if (llist_add((struct llist_node *)&page->mapping,
+ &hpage_freelist))
+ schedule_work(&free_hpage_work);
+ return;
+ }
+
+ __free_huge_page(page);
+}
+
static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
{
INIT_LIST_HEAD(&page->lru);