Mailing List Archive

# HG changeset patch
# User kaf24@firebug.cl.cam.ac.uk
# Node ID af38c6b205f6f1bfb13310647b95b7557ab0e574
# Parent 9d47f70345a480caf4c2b7210de60179c2f31198
Keir moved barriers,
Competence questions are raised:
Correctness withers.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff -r 9d47f70345a4 -r af38c6b205f6 linux-2.6-xen-sparse/drivers/xen/xenbus/xenbus_comms.c
--- a/linux-2.6-xen-sparse/drivers/xen/xenbus/xenbus_comms.c Wed Oct 12 15:42:35 2005
+++ b/linux-2.6-xen-sparse/drivers/xen/xenbus/xenbus_comms.c Wed Oct 12 16:00:29 2005
@@ -130,7 +130,7 @@

wait_event_interruptible(xb_waitq, output_avail(out));

- mb();
+ /* Make local copy of header to check for sanity. */
h = *out;
if (!check_buffer(&h))
return -EIO;
@@ -140,10 +140,20 @@
continue;
if (avail > len)
avail = len;
+
+ /* Make sure we read header before we write data
+ * (implied by data-dependency, but let's play safe). */
+ mb();
+
memcpy(dst, data, avail);
data += avail;
len -= avail;
+
+ /* Other side must not see new header until data is there. */
+ wmb();
update_output_chunk(out, avail);
+
+ /* This implies mb() before other side sees interrupt. */
notify_remote_via_evtchn(xen_start_info->store_evtchn);
} while (len != 0);

@@ -171,7 +181,6 @@

wait_event_interruptible(xb_waitq, xs_input_avail());

- mb();
h = *in;
if (!check_buffer(&h))
return -EIO;
@@ -183,13 +192,21 @@
avail = len;
was_full = !output_avail(&h);

+ /* We must read header before we read data. */
+ rmb();
+
memcpy(data, src, avail);
data += avail;
len -= avail;
+
+ /* Other side must not see free space until we've copied out */
+ mb();
+
update_input_chunk(in, avail);
pr_debug("Finished read of %i bytes (%i to go)\n", avail, len);
/* If it was full, tell them we've taken some. */
if (was_full)
+ /* Implies mb(): they will see new header. */
notify_remote_via_evtchn(xen_start_info->store_evtchn);
}


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