Date: Thu, 27 Dec 2012 12:36:58 +0000 (UTC) From: Attilio Rao <attilio@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r244732 - head/sys/sys Message-ID: <201212271236.qBRCawuU078203@svn.freebsd.org>
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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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