linux-kernel - [PATCH] z3fold: fix memory leak in kmem cache

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Date:   Tue, 17 Sep 2019 18:53:52 +0300
From:   Vitaly Wool <vitalywool@...il.com>
To:     Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Cc:     Dan Streetman <ddstreet@...e.org>,
        Vlastimil Babka <vbabka@...e.cz>, markus.linnala@...il.com
Subject: [PATCH] z3fold: fix memory leak in kmem cache

Currently there is a leak in init_z3fold_page() -- it allocates
handles from kmem cache even for headless pages, but then they are
never used and never freed, so eventually kmem cache may get
exhausted. This patch provides a fix for that.

Reported-by: Markus Linnala <markus.linnala@...il.com>
Signed-off-by: Vitaly Wool <vitalywool@...il.com>
---
 mm/z3fold.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 6397725b5ec6..7dffef2599c3 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -301,14 +301,11 @@ static void z3fold_unregister_migration(struct z3fold_pool *pool)
  }
 
 /* Initializes the z3fold header of a newly allocated z3fold page */
-static struct z3fold_header *init_z3fold_page(struct page *page,
+static struct z3fold_header *init_z3fold_page(struct page *page, bool headless,
 					struct z3fold_pool *pool, gfp_t gfp)
 {
 	struct z3fold_header *zhdr = page_address(page);
-	struct z3fold_buddy_slots *slots = alloc_slots(pool, gfp);
-
-	if (!slots)
-		return NULL;
+	struct z3fold_buddy_slots *slots;
 
 	INIT_LIST_HEAD(&page->lru);
 	clear_bit(PAGE_HEADLESS, &page->private);
@@ -316,6 +313,12 @@ static struct z3fold_header *init_z3fold_page(struct page *page,
 	clear_bit(NEEDS_COMPACTING, &page->private);
 	clear_bit(PAGE_STALE, &page->private);
 	clear_bit(PAGE_CLAIMED, &page->private);
+	if (headless)
+		return zhdr;
+
+	slots = alloc_slots(pool, gfp);
+	if (!slots)
+		return NULL;
 
 	spin_lock_init(&zhdr->page_lock);
 	kref_init(&zhdr->refcount);
@@ -962,7 +965,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
 	if (!page)
 		return -ENOMEM;
 
-	zhdr = init_z3fold_page(page, pool, gfp);
+	zhdr = init_z3fold_page(page, bud == HEADLESS, pool, gfp);
 	if (!zhdr) {
 		__free_page(page);
 		return -ENOMEM;
-- 
2.17.1