linux-kernel - [PATCH 2/2] z3fold: fix locking issues

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sat, 26 Nov 2016 20:21:21 +0100
From:   Vitaly Wool <vitalywool@...il.com>
To:     Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org
Cc:     Dan Streetman <ddstreet@...e.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: [PATCH 2/2] z3fold: fix locking issues

Commit 570931c ("z3fold: use per-page spinlock") introduced locking
issues in reclaim function reported in [1] and [2]. This patch
addresses these issues, also fixing the check for empty lru list
(it was only checked once, while it should be checked every time
we want to get the last lru entry).

[1] https://lkml.org/lkml/2016/11/25/628
[2] http://www.spinics.net/lists/linux-mm/msg117227.html

Signed-off-by: Vitaly Wool <vitalywool@...il.com>
---
 mm/z3fold.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index efbcfcc..729a2da 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -607,12 +607,15 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 	unsigned long first_handle = 0, middle_handle = 0, last_handle = 0;
 
 	spin_lock(&pool->lock);
-	if (!pool->ops || !pool->ops->evict || list_empty(&pool->lru) ||
-			retries == 0) {
+	if (!pool->ops || !pool->ops->evict || retries == 0) {
 		spin_unlock(&pool->lock);
 		return -EINVAL;
 	}
 	for (i = 0; i < retries; i++) {
+		if (list_empty(&pool->lru)) {
+			spin_unlock(&pool->lock);
+			return -EINVAL;
+		}
 		page = list_last_entry(&pool->lru, struct page, lru);
 		list_del(&page->lru);
 
@@ -671,8 +674,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 			 * All buddies are now free, free the z3fold page and
 			 * return success.
 			 */
-			clear_bit(PAGE_HEADLESS, &page->private);
-			if (!test_bit(PAGE_HEADLESS, &page->private))
+			if (!test_and_clear_bit(PAGE_HEADLESS, &page->private))
 				z3fold_page_unlock(zhdr);
 			free_z3fold_page(zhdr);
 			atomic64_dec(&pool->pages_nr);
@@ -684,6 +686,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 				/* Full, add to buddied list */
 				spin_lock(&pool->lock);
 				list_add(&zhdr->buddy, &pool->buddied);
+				spin_unlock(&pool->lock);
 			} else {
 				z3fold_compact_page(zhdr);
 				/* add to unbuddied list */
@@ -691,15 +694,18 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 				freechunks = num_free_chunks(zhdr);
 				list_add(&zhdr->buddy,
 					 &pool->unbuddied[freechunks]);
+				spin_unlock(&pool->lock);
 			}
 		}
 
+		if (!test_bit(PAGE_HEADLESS, &page->private))
+			z3fold_page_unlock(zhdr);
+
+		spin_lock(&pool->lock);
 		/* add to beginning of LRU */
 		list_add(&page->lru, &pool->lru);
 	}
 	spin_unlock(&pool->lock);
-	if (!test_bit(PAGE_HEADLESS, &page->private))
-		z3fold_page_unlock(zhdr);
 	return -EAGAIN;
 }
 
-- 
2.4.2