[Xen-changelog] Watch events may get lost, the xenstored response races against the new

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID ea6d9f29dff5d429c0a7cb6c381628e6f2bb38e1
# Parent  8cc7ce549d00bef90a568ed64a0309cec3d399e9
Watch events may get lost, the xenstored response races against the new 
watch being added to the watch list in register_xenbus_watch().  Fixed 
by adding the watch to the list unconditionally, and remove it in the 
error case.

diff -r 8cc7ce549d00 -r ea6d9f29dff5 
linux-2.6-xen-sparse/drivers/xen/xenbus/xenbus_xs.c
--- a/linux-2.6-xen-sparse/drivers/xen/xenbus/xenbus_xs.c       Mon Oct 31 
09:45:31 2005
+++ b/linux-2.6-xen-sparse/drivers/xen/xenbus/xenbus_xs.c       Mon Oct 31 
16:07:14 2005
@@ -682,14 +682,15 @@
 
        spin_lock(&watches_lock);
        BUG_ON(find_watch(token));
+       list_add(&watch->list, &watches);
        spin_unlock(&watches_lock);
 
        err = xs_watch(watch->node, token);
 
        /* Ignore errors due to multiple registration. */
-       if ((err == 0) || (err == -EEXIST)) {
+       if ((err != 0) && (err != -EEXIST)) {
                spin_lock(&watches_lock);
-               list_add(&watch->list, &watches);
+               list_del(&watch->list);
                spin_unlock(&watches_lock);
        }
 

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