IB/core: use RCU for uverbs id lookup
The current implementation gets a spin_lock, and at any scale with
qib and hfi1 post send, the lock contention grows exponentially
with the number of QPs.
idr_find() is RCU compatibile, so read doesn't need the lock.
Change to use rcu_read_lock() and rcu_read_unlock() in
__idr_get_uobj().
kfree_rcu() is used to insure a grace period between the
idr removal and actual free.
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-By: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
index 4cb8e9d..1c02dea 100644
--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -62,9 +62,11 @@
* The ib_uobject locking scheme is as follows:
*
* - ib_uverbs_idr_lock protects the uverbs idrs themselves, so it
- * needs to be held during all idr operations. When an object is
+ * needs to be held during all idr write operations. When an object is
* looked up, a reference must be taken on the object's kref before
- * dropping this lock.
+ * dropping this lock. For read operations, the rcu_read_lock()
+ * and rcu_write_lock() but similarly the kref reference is grabbed
+ * before the rcu_read_unlock().
*
* - Each object also has an rwsem. This rwsem must be held for
* reading while an operation that uses the object is performed.
@@ -96,7 +98,7 @@
static void release_uobj(struct kref *kref)
{
- kfree(container_of(kref, struct ib_uobject, ref));
+ kfree_rcu(container_of(kref, struct ib_uobject, ref), rcu);
}
static void put_uobj(struct ib_uobject *uobj)
@@ -145,7 +147,7 @@
{
struct ib_uobject *uobj;
- spin_lock(&ib_uverbs_idr_lock);
+ rcu_read_lock();
uobj = idr_find(idr, id);
if (uobj) {
if (uobj->context == context)
@@ -153,7 +155,7 @@
else
uobj = NULL;
}
- spin_unlock(&ib_uverbs_idr_lock);
+ rcu_read_unlock();
return uobj;
}
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 9a68a19..120da1d 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -1271,6 +1271,7 @@
int id; /* index into kernel idr */
struct kref ref;
struct rw_semaphore mutex; /* protects .live */
+ struct rcu_head rcu; /* kfree_rcu() overhead */
int live;
};