Re: [PATCH] mm/zswap: fix potential deadlock in zswap_frontswap_store()
From: Shakeel Butt <hidden>
Date: 2017-03-31 17:00:33
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lkml
On Fri, Mar 31, 2017 at 8:30 AM, Andrey Ryabinin [off-list ref] wrote:
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.
Is it possible to enter fs code (or IO) from zswap_frontswap_store() other than recursive memory reclaim? However recursive memory reclaim is protected through PF_MEMALLOC task flag. The change seems fine but IMHO reasoning needs an update. Adding Michal for expert opinion.
quoted hunk ↗ jump to hunk
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 <redacted> --- 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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