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Subject[PATCH] mm/zswap: fix potential deadlock in zswap_frontswap_store()
Date
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@virtuozzo.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
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