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authorNeilBrown <neilb@suse.com>2018-11-30 10:26:50 +1100
committerDavid S. Miller <davem@davemloft.net>2018-12-03 15:31:55 -0800
commit82208d0d54ab85d8fedbb1c9a1960bd401a4ca1a (patch)
tree03fa10ee2af45f2ab285791484515b9ac39411c9 /lib/rhashtable.c
parent77ac327c54692306e71063131cd4721769badc65 (diff)
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rhashtable: detect when object movement between tables might have invalidated a lookup
Some users of rhashtables might need to move an object from one table to another - this appears to be the reason for the incomplete usage of NULLS markers. To support these, we store a unique NULLS_MARKER at the end of each chain, and when a search fails to find a match, we check if the NULLS marker found was the expected one. If not, the search may not have examined all objects in the target bucket, so it is repeated. The unique NULLS_MARKER is derived from the address of the head of the chain. As this cannot be derived at load-time the static rhnull in rht_bucket_nested() needs to be initialised at run time. Any caller of a lookup function must still be prepared for the possibility that the object returned is in a different table - it might have been there for some time. Note that this does NOT provide support for other uses of NULLS_MARKERs such as allocating with SLAB_TYPESAFE_BY_RCU or changing the key of an object and re-inserting it in the same table. These could only be done safely if new objects were inserted at the *start* of a hash chain, and that is not currently the case. Signed-off-by: NeilBrown <neilb@suse.com> Acked-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'lib/rhashtable.c')
-rw-r--r--lib/rhashtable.c8
1 files changed, 5 insertions, 3 deletions
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 30526afa8343..852ffa5160f1 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -1179,8 +1179,7 @@ struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
unsigned int hash)
{
const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
- static struct rhash_head __rcu *rhnull =
- (struct rhash_head __rcu *)NULLS_MARKER(0);
+ static struct rhash_head __rcu *rhnull;
unsigned int index = hash & ((1 << tbl->nest) - 1);
unsigned int size = tbl->size >> tbl->nest;
unsigned int subhash = hash;
@@ -1198,8 +1197,11 @@ struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
subhash >>= shift;
}
- if (!ntbl)
+ if (!ntbl) {
+ if (!rhnull)
+ INIT_RHT_NULLS_HEAD(rhnull);
return &rhnull;
+ }
return &ntbl[subhash].bucket;