From: Mike Marciniszyn <mike.marciniszyn@xxxxxxxxx>
The synchronize_rcu() call can be eliminated to improve memory deregistration
performance.
There are two key fields involved:
- The rcu pointer itself
- the lkey_published field
To close the window between the rcu read of the mregion pointer and the
reference count the code should:
1. To lkey/rkey validation (reader)
Read the rcu pointer. If the pointer is non-NULL, get a reference.
To the current validation tests use a READ_ONCE() on the lkey_published.
Upon any failure release the reference.
2. To the remove logic (delete)
Insure the published is zeroed prior to setting the pointer to NULL.
This requires using rcu_assign_pointer() to insure lkey_published
is written prior to the NULL.
3. To the insert logic (add)
Insure the published is set use an rcu_assign_pointer() to insure the
pointer is after all MR fields.
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@xxxxxxxxx>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@xxxxxxxxx>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@xxxxxxxxx>
---
drivers/infiniband/sw/rdmavt/mr.c | 49 +++++++++++++++++++++++++------------
1 files changed, 33 insertions(+), 16 deletions(-)
diff --git a/drivers/infiniband/sw/rdmavt/mr.c b/drivers/infiniband/sw/rdmavt/mr.c
index ae30b68..7c86955 100644
--- a/drivers/infiniband/sw/rdmavt/mr.c
+++ b/drivers/infiniband/sw/rdmavt/mr.c
@@ -191,8 +191,9 @@ static int rvt_alloc_lkey(struct rvt_mregion *mr, int dma_region)
tmr = rcu_access_pointer(dev->dma_mr);
if (!tmr) {
- rcu_assign_pointer(dev->dma_mr, mr);
mr->lkey_published = 1;
+ /* Insure published written first */
+ rcu_assign_pointer(dev->dma_mr, mr);
rvt_get_mr(mr);
}
goto success;
@@ -224,8 +225,9 @@ static int rvt_alloc_lkey(struct rvt_mregion *mr, int dma_region)
mr->lkey |= 1 << 8;
rkt->gen++;
}
- rcu_assign_pointer(rkt->table[r], mr);
mr->lkey_published = 1;
+ /* Insure published written first */
+ rcu_assign_pointer(rkt->table[r], mr);
success:
spin_unlock_irqrestore(&rkt->lock, flags);
out:
@@ -253,23 +255,24 @@ static void rvt_free_lkey(struct rvt_mregion *mr)
spin_lock_irqsave(&rkt->lock, flags);
if (!lkey) {
if (mr->lkey_published) {
- RCU_INIT_POINTER(dev->dma_mr, NULL);
+ mr->lkey_published = 0;
+ /* insure published is written before pointer */
+ rcu_assign_pointer(dev->dma_mr, NULL);
rvt_put_mr(mr);
}
} else {
if (!mr->lkey_published)
goto out;
r = lkey >> (32 - dev->dparms.lkey_table_size);
- RCU_INIT_POINTER(rkt->table[r], NULL);
+ mr->lkey_published = 0;
+ /* insure published is written before pointer */
+ rcu_assign_pointer(rkt->table[r], NULL);
}
- mr->lkey_published = 0;
freed++;
out:
spin_unlock_irqrestore(&rkt->lock, flags);
- if (freed) {
- synchronize_rcu();
+ if (freed)
percpu_ref_kill(&mr->refcount);
- }
}
static struct rvt_mr *__rvt_alloc_mr(int count, struct ib_pd *pd)
@@ -822,16 +825,21 @@ int rvt_lkey_ok(struct rvt_lkey_table *rkt, struct rvt_pd *pd,
goto ok;
}
mr = rcu_dereference(rkt->table[sge->lkey >> rkt->shift]);
- if (unlikely(!mr || atomic_read(&mr->lkey_invalid) ||
- mr->lkey != sge->lkey || mr->pd != &pd->ibpd))
+ if (!mr)
goto bail;
+ rvt_get_mr(mr);
+ if (!READ_ONCE(mr->lkey_published))
+ goto bail_unref;
+
+ if (unlikely(atomic_read(&mr->lkey_invalid) ||
+ mr->lkey != sge->lkey || mr->pd != &pd->ibpd))
+ goto bail_unref;
off = sge->addr - mr->user_base;
if (unlikely(sge->addr < mr->user_base ||
off + sge->length > mr->length ||
(mr->access_flags & acc) != acc))
- goto bail;
- rvt_get_mr(mr);
+ goto bail_unref;
rcu_read_unlock();
off += mr->offset;
@@ -867,6 +875,8 @@ int rvt_lkey_ok(struct rvt_lkey_table *rkt, struct rvt_pd *pd,
isge->n = n;
ok:
return 1;
+bail_unref:
+ rvt_put_mr(mr);
bail:
rcu_read_unlock();
return 0;
@@ -922,15 +932,20 @@ int rvt_rkey_ok(struct rvt_qp *qp, struct rvt_sge *sge,
}
mr = rcu_dereference(rkt->table[rkey >> rkt->shift]);
- if (unlikely(!mr || atomic_read(&mr->lkey_invalid) ||
- mr->lkey != rkey || qp->ibqp.pd != mr->pd))
+ if (!mr)
goto bail;
+ rvt_get_mr(mr);
+ /* insure mr read is before test */
+ if (!READ_ONCE(mr->lkey_published))
+ goto bail_unref;
+ if (unlikely(atomic_read(&mr->lkey_invalid) ||
+ mr->lkey != rkey || qp->ibqp.pd != mr->pd))
+ goto bail_unref;
off = vaddr - mr->iova;
if (unlikely(vaddr < mr->iova || off + len > mr->length ||
(mr->access_flags & acc) == 0))
- goto bail;
- rvt_get_mr(mr);
+ goto bail_unref;
rcu_read_unlock();
off += mr->offset;
@@ -966,6 +981,8 @@ int rvt_rkey_ok(struct rvt_qp *qp, struct rvt_sge *sge,
sge->n = n;
ok:
return 1;
+bail_unref:
+ rvt_put_mr(mr);
bail:
rcu_read_unlock();
return 0;
--
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