path: root/.clang-format
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authorNeilBrown <>2019-03-21 14:42:40 +1100
committerDavid S. Miller <>2019-03-21 14:01:10 -0700
commit4feb7c7a4fbb8f63371be31cda79433c7cf3da86 (patch)
tree634aa8dd79c50984306f29738f2a19287a97013d /.clang-format
parent83b038db255d83a32c15fd003f9a921204b9215a (diff)
rhashtable: don't hold lock on first table throughout insertion.
rhashtable_try_insert() currently holds a lock on the bucket in the first table, while also locking buckets in subsequent tables. This is unnecessary and looks like a hold-over from some earlier version of the implementation. As insert and remove always lock a bucket in each table in turn, and as insert only inserts in the final table, there cannot be any races that are not covered by simply locking a bucket in each table in turn. When an insert call reaches that last table it can be sure that there is no matchinf entry in any other table as it has searched them all, and insertion never happens anywhere but in the last table. The fact that code tests for the existence of future_tbl while holding a lock on the relevant bucket ensures that two threads inserting the same key will make compatible decisions about which is the "last" table. This simplifies the code and allows the ->rehash field to be discarded. We still need a way to ensure that a dead bucket_table is never re-linked by rhashtable_walk_stop(). This can be achieved by calling call_rcu() inside the locked region, and checking with rcu_head_after_call_rcu() in rhashtable_walk_stop() to see if the bucket table is empty and dead. Acked-by: Herbert Xu <> Reviewed-by: Paul E. McKenney <> Signed-off-by: NeilBrown <> Signed-off-by: David S. Miller <>
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