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>
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@ -62,9 +62,11 @@ static struct uverbs_lock_class rule_lock_class = { .name = "RULE-uobj" };
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* The ib_uobject locking scheme is as follows:
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* The ib_uobject locking scheme is as follows:
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*
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*
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* - ib_uverbs_idr_lock protects the uverbs idrs themselves, so it
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* - ib_uverbs_idr_lock protects the uverbs idrs themselves, so it
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* needs to be held during all idr operations. When an object is
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* needs to be held during all idr write operations. When an object is
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* looked up, a reference must be taken on the object's kref before
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* looked up, a reference must be taken on the object's kref before
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* dropping this lock.
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* dropping this lock. For read operations, the rcu_read_lock()
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* and rcu_write_lock() but similarly the kref reference is grabbed
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* before the rcu_read_unlock().
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*
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*
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* - Each object also has an rwsem. This rwsem must be held for
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* - Each object also has an rwsem. This rwsem must be held for
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* reading while an operation that uses the object is performed.
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* reading while an operation that uses the object is performed.
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@ -96,7 +98,7 @@ static void init_uobj(struct ib_uobject *uobj, u64 user_handle,
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static void release_uobj(struct kref *kref)
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static void release_uobj(struct kref *kref)
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{
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{
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kfree(container_of(kref, struct ib_uobject, ref));
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kfree_rcu(container_of(kref, struct ib_uobject, ref), rcu);
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}
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}
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static void put_uobj(struct ib_uobject *uobj)
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static void put_uobj(struct ib_uobject *uobj)
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@ -145,7 +147,7 @@ static struct ib_uobject *__idr_get_uobj(struct idr *idr, int id,
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{
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{
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struct ib_uobject *uobj;
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struct ib_uobject *uobj;
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spin_lock(&ib_uverbs_idr_lock);
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rcu_read_lock();
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uobj = idr_find(idr, id);
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uobj = idr_find(idr, id);
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if (uobj) {
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if (uobj) {
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if (uobj->context == context)
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if (uobj->context == context)
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@ -153,7 +155,7 @@ static struct ib_uobject *__idr_get_uobj(struct idr *idr, int id,
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else
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else
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uobj = NULL;
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uobj = NULL;
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}
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}
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spin_unlock(&ib_uverbs_idr_lock);
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rcu_read_unlock();
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return uobj;
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return uobj;
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}
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}
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@ -1271,6 +1271,7 @@ struct ib_uobject {
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int id; /* index into kernel idr */
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int id; /* index into kernel idr */
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struct kref ref;
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struct kref ref;
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struct rw_semaphore mutex; /* protects .live */
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struct rw_semaphore mutex; /* protects .live */
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struct rcu_head rcu; /* kfree_rcu() overhead */
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int live;
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int live;
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};
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};
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