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br_prod_tail and br_cons_tail members are used as barrier to

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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
This commit is contained in:
Attilio Rao 2012-12-27 12:36:58 +00:00
parent 9aff36d897
commit 30c7dd147c
1 changed files with 5 additions and 5 deletions
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10
sys/sys/buf_ring.h
View file

@ -114,10 +114,10 @@ buf_ring_enqueue(struct buf_ring *br, void *buf)
* 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);
}