From 2d22ecf6db1c390974476758681ba4229018e774 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Tue, 21 Aug 2018 22:01:48 -0700 Subject: lib/rhashtable: guarantee initial hashtable allocation rhashtable_init() may fail due to -ENOMEM, thus making the entire api unusable. This patch removes this scenario, however unlikely. In order to guarantee memory allocation, this patch always ends up doing GFP_KERNEL|__GFP_NOFAIL for both the tbl as well as alloc_bucket_spinlocks(). Upon the first table allocation failure, we shrink the size to the smallest value that makes sense and retry with __GFP_NOFAIL semantics. With the defaults, this means that from 64 buckets, we retry with only 4. Any later issues regarding performance due to collisions or larger table resizing (when more memory becomes available) is the least of our problems. Link: http://lkml.kernel.org/r/20180712185241.4017-9-manfred@colorfullife.com Signed-off-by: Davidlohr Bueso Signed-off-by: Manfred Spraul Acked-by: Herbert Xu Cc: Dmitry Vyukov Cc: Kees Cook Cc: Michael Kerrisk Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/rhashtable.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/lib/rhashtable.c b/lib/rhashtable.c index 238c8daa9852..310e29b51507 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -178,10 +178,11 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht, size = nbuckets; - if (tbl == NULL && gfp != GFP_KERNEL) { + if (tbl == NULL && (gfp & ~__GFP_NOFAIL) != GFP_KERNEL) { tbl = nested_bucket_table_alloc(ht, nbuckets, gfp); nbuckets = 0; } + if (tbl == NULL) return NULL; @@ -1057,9 +1058,16 @@ int rhashtable_init(struct rhashtable *ht, } } + /* + * This is api initialization and thus we need to guarantee the + * initial rhashtable allocation. Upon failure, retry with the + * smallest possible size with __GFP_NOFAIL semantics. + */ tbl = bucket_table_alloc(ht, size, GFP_KERNEL); - if (tbl == NULL) - return -ENOMEM; + if (unlikely(tbl == NULL)) { + size = max_t(u16, ht->p.min_size, HASH_MIN_SIZE); + tbl = bucket_table_alloc(ht, size, GFP_KERNEL | __GFP_NOFAIL); + } atomic_set(&ht->nelems, 0); -- cgit v1.2.1