linux-kernel - [PATCH] mm/zswap: fix potential deadlock in zswap_frontswap

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Date:   Fri, 31 Mar 2017 18:30:09 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <akpm@...ux-foundation.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: [PATCH] mm/zswap: fix potential deadlock in zswap_frontswap_store()

zswap_frontswap_store() is called during memory reclaim from
__frontswap_store() from swap_writepage() from shrink_page_list().
This may happen in NOFS context, thus zswap shouldn't use __GFP_FS,
otherwise we may renter into fs code and deadlock.
zswap_frontswap_store() also shouldn't use __GFP_IO to avoid recursion
into itself.

zswap_frontswap_store() call zpool_malloc() with __GFP_NORETRY |
__GFP_NOWARN | __GFP_KSWAPD_RECLAIM, so let's use the same flags for
zswap_entry_cache_alloc() as well, instead of GFP_KERNEL.

Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
---
 mm/zswap.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index eedc278..12ad7e9 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -966,6 +966,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 	struct zswap_tree *tree = zswap_trees[type];
 	struct zswap_entry *entry, *dupentry;
 	struct crypto_comp *tfm;
+	gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
 	int ret;
 	unsigned int dlen = PAGE_SIZE, len;
 	unsigned long handle;
@@ -989,7 +990,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 	}
 
 	/* allocate entry */
-	entry = zswap_entry_cache_alloc(GFP_KERNEL);
+	entry = zswap_entry_cache_alloc(gfp);
 	if (!entry) {
 		zswap_reject_kmemcache_fail++;
 		ret = -ENOMEM;
@@ -1017,9 +1018,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 
 	/* store */
 	len = dlen + sizeof(struct zswap_header);
-	ret = zpool_malloc(entry->pool->zpool, len,
-			   __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM,
-			   &handle);
+	ret = zpool_malloc(entry->pool->zpool, len, gfp, &handle);
 	if (ret == -ENOSPC) {
 		zswap_reject_compress_poor++;
 		goto put_dstmem;
-- 
2.10.2