Author: attilio
Date: Thu Dec 27 12:36:58 2012
New Revision: 244732
URL: http://svnweb.freebsd.org/changeset/base/244732
Log:
br_prod_tail and br_cons_tail members are used as barrier to
signal bug_ring ownership. However, instructions can be reordered
around members write leading to stale values for ie. br_prod_bufs.
Use correct memory barriers to ensure proper ordering of the
ownership tokens updates.
Sponsored by: EMC / Isilon storage division
MFC after: 2 weeks
Modified:
head/sys/sys/buf_ring.h
Modified: head/sys/sys/buf_ring.h
==============================================================================
--- head/sys/sys/buf_ring.h Thu Dec 27 09:15:21 2012 (r244731)
+++ head/sys/sys/buf_ring.h Thu Dec 27 12:36:58 2012 (r244732)
@@ -114,10 +114,10 @@ buf_ring_enqueue(struct buf_ring *br, vo
* that preceeded us, we need to wait for them
* to complete
*/
- while (br->br_prod_tail != prod_head)
+ while (atomic_load_acq_32(&br->br_prod_tail) != prod_head)
cpu_spinwait();
br->br_prod_bufs++;
- br->br_prod_tail = prod_next;
+ atomic_store_rel_32(&br->br_prod_tail, prod_next);
critical_exit();
return (0);
}
@@ -161,10 +161,10 @@ buf_ring_dequeue_mc(struct buf_ring *br)
* that preceeded us, we need to wait for them
* to complete
*/
- while (br->br_cons_tail != cons_head)
+ while (atomic_load_acq_32(&br->br_cons_tail) != cons_head)
cpu_spinwait();
- br->br_cons_tail = cons_next;
+ atomic_store_rel_32(&br->br_cons_tail, cons_next);
critical_exit();
return (buf);
@@ -209,7 +209,7 @@ buf_ring_dequeue_sc(struct buf_ring *br)
panic("inconsistent list cons_tail=%d cons_head=%d",
br->br_cons_tail, cons_head);
#endif
- br->br_cons_tail = cons_next;
+ atomic_store_rel_32(&br->br_cons_tail, cons_next);
return (buf);
}
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