On Wed, Jan 03, 2007 at 01:22:32PM -0800, Andrew Morton wrote:
> It's nice to always have a comment explaining the use of open-coded
> barriers. Because often the reader is left wondered what on earth it's
> barriering against what on earth else.
>
Ok, here it is...
Andrew asked that the open-coded barriers be commented, so here it
is. I also realized that one of the read barriers was in an area
where the protecting mutex was held, so no read barrier was needed.
Signed-off-by: Corey Minyard <[email protected]>
Index: linux-2.6.19/drivers/char/ipmi/ipmi_msghandler.c
===================================================================
--- linux-2.6.19.orig/drivers/char/ipmi/ipmi_msghandler.c
+++ linux-2.6.19/drivers/char/ipmi/ipmi_msghandler.c
@@ -839,7 +839,6 @@ int ipmi_create_user(unsigned int
goto out_kfree;
found:
- smp_rmb();
/* Note that each existing user holds a refcount to the interface. */
kref_get(&intf->refcount);
@@ -2762,10 +2761,15 @@ int ipmi_register_smi(struct ipmi_smi_ha
synchronize_rcu();
kref_put(&intf->refcount, intf_free);
} else {
- /* After this point the interface is legal to use. */
- smp_wmb(); /* Keep memory order straight for RCU readers. */
+ /*
+ * Keep memory order straight for RCU readers. Make
+ * sure everything else is committed to memory before
+ * setting intf_num to mark the interface valid.
+ */
+ smp_wmb();
intf->intf_num = i;
mutex_unlock(&ipmi_interfaces_mutex);
+ /* After this point the interface is legal to use. */
call_smi_watchers(i, intf->si_dev);
mutex_unlock(&smi_watchers_mutex);
}
@@ -3927,6 +3931,12 @@ static void send_panic_events(char *str)
/* Interface was not ready yet. */
continue;
+ /*
+ * intf_num is used as an marker to tell if the
+ * interface is valid. Thus we need a read barrier to
+ * make sure data fetched before checking intf_num
+ * won't be used.
+ */
smp_rmb();
/* First job here is to figure out where to send the
-
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