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Commit d144da8c authored by Mike Marciniszyn's avatar Mike Marciniszyn Committed by Doug Ledford
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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: default avatarIra Weiny <ira.weiny@intel.com>
Signed-off-by: default avatarMike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-By: default avatarJason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: default avatarDoug Ledford <dledford@redhat.com>
parent 57ab2512

drivers/infiniband/core/uverbs_cmd.c

+7 −5
Original line number Diff line number Diff line
@@ -62,9 +62,11 @@ static struct uverbs_lock_class rule_lock_class = { .name = "RULE-uobj" }; 
 * 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 init_uobj(struct ib_uobject *uobj, u64 user_handle, 


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 @@ static struct ib_uobject *__idr_get_uobj(struct idr *idr, int id, 
{

	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 @@ static struct ib_uobject *__idr_get_uobj(struct idr *idr, int id, 
		else

			uobj = NULL;

	}

	spin_unlock(&ib_uverbs_idr_lock);

	rcu_read_unlock();



	return uobj;

}

include/rdma/ib_verbs.h

+1 −0
Original line number Diff line number Diff line
@@ -1271,6 +1271,7 @@ struct ib_uobject { 
	int			id;		/* index into kernel idr */

	struct kref		ref;

	struct rw_semaphore	mutex;		/* protects .live */

	struct rcu_head		rcu;		/* kfree_rcu() overhead */

	int			live;

};