From e2307ed6cbe71c74e291681aaa7e92ab98bc3177 Mon Sep 17 00:00:00 2001 From: Thomas Graf Date: Wed, 22 Apr 2015 09:41:45 +0200 Subject: rhashtable: Schedule async resize when sync realloc fails When rhashtable_insert_rehash() fails with ENOMEM, this indicates that we can't allocate the necessary memory in the current context but the limits as set by the user would still allow to grow. Thus attempt an async resize in the background where we can allocate using GFP_KERNEL which is more likely to succeed. The insertion itself will still fail to indicate pressure. This fixes a bug where the table would never continue growing once the utilization is above 100%. Fixes: ccd57b1bd324 ("rhashtable: Add immediate rehash during insertion") Signed-off-by: Thomas Graf Acked-by: Herbert Xu Signed-off-by: David S. Miller --- lib/rhashtable.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'lib') diff --git a/lib/rhashtable.c b/lib/rhashtable.c index 4898442..f648cfd 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -410,8 +410,13 @@ int rhashtable_insert_rehash(struct rhashtable *ht) return -EBUSY; new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC); - if (new_tbl == NULL) + if (new_tbl == NULL) { + /* Schedule async resize/rehash to try allocation + * non-atomic context. + */ + schedule_work(&ht->run_work); return -ENOMEM; + } err = rhashtable_rehash_attach(ht, tbl, new_tbl); if (err) { -- cgit v1.1 From a87b9ebf1709687ff213091d0fdb4254b1564803 Mon Sep 17 00:00:00 2001 From: Thomas Graf Date: Wed, 22 Apr 2015 09:41:46 +0200 Subject: rhashtable: Do not schedule more than one rehash if we can't grow further The current code currently only stops inserting rehashes into the chain when no resizes are currently scheduled. As long as resizes are scheduled and while inserting above the utilization watermark, more and more rehashes will be scheduled. This lead to a perfect DoS storm with thousands of rehashes scheduled which lead to thousands of spinlocks to be taken sequentially. Instead, only allow either a series of resizes or a single rehash. Drop any further rehashes and return -EBUSY. Fixes: ccd57b1bd324 ("rhashtable: Add immediate rehash during insertion") Signed-off-by: Thomas Graf Acked-by: Herbert Xu Signed-off-by: David S. Miller --- lib/rhashtable.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'lib') diff --git a/lib/rhashtable.c b/lib/rhashtable.c index f648cfd..b28df40 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -405,8 +405,8 @@ int rhashtable_insert_rehash(struct rhashtable *ht) if (rht_grow_above_75(ht, tbl)) size *= 2; - /* More than two rehashes (not resizes) detected. */ - else if (WARN_ON(old_tbl != tbl && old_tbl->size == size)) + /* Do not schedule more than one rehash */ + else if (old_tbl != tbl) return -EBUSY; new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC); -- cgit v1.1