[xen staging] tools/xenstored: Ignore domain we were unable to restore

[patchbot@xxxxxxx]

commit 98f60e5de00baf650c574c9352bb19aedb082dea
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Wed Oct 20 14:45:19 2021 +0000
Commit:     Ian Jackson <iwj@xxxxxxxxxxxxxx>
CommitDate: Thu Oct 21 11:52:12 2021 +0100

    tools/xenstored: Ignore domain we were unable to restore
    
    Commit 939775cfd3 "handle dying domains in live update" was meant to
    handle gracefully dying domain. However, the @releaseDomain watch
    will end up to be sent as soon as we finished to restore Xenstored
    state.
    
    This may be before Xen reports the domain to be dying (such as if
    the guest decided to revoke access to the xenstore page). Consequently
    daemon like xenconsoled will not clean-up the domain and it will be
    left as a zombie.
    
    To avoid the problem, mark the connection as ignored. This also
    requires to tweak conn_can_write() and conn_can_read() to prevent
    dereferencing a NULL pointer (the interface will not mapped).
    
    The check conn->is_ignored was originally added after the callbacks
    because the helpers for a socket connection may close the fd. However,
    ignore_connection() will close a socket connection directly. So it is
    fine to do the re-order.
    
    Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
    Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
---
 tools/xenstore/xenstored_core.c   |  8 ++++----
 tools/xenstore/xenstored_core.h   |  1 +
 tools/xenstore/xenstored_domain.c | 21 ++++++++++++---------
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 0d4c73d6e2..91d093a12e 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -338,10 +338,10 @@ static int destroy_conn(void *_conn)
 
 static bool conn_can_read(struct connection *conn)
 {
-       if (!conn->funcs->can_read(conn))
+       if (conn->is_ignored)
                return false;
 
-       if (conn->is_ignored)
+       if (!conn->funcs->can_read(conn))
                return false;
 
        /*
@@ -356,7 +356,7 @@ static bool conn_can_read(struct connection *conn)
 
 static bool conn_can_write(struct connection *conn)
 {
-       return conn->funcs->can_write(conn) && !conn->is_ignored;
+       return !conn->is_ignored && conn->funcs->can_write(conn);
 }
 
 /* This function returns index inside the array if succeed, -1 if fail */
@@ -1466,7 +1466,7 @@ static struct {
  *
  * All watches, transactions, buffers will be freed.
  */
-static void ignore_connection(struct connection *conn)
+void ignore_connection(struct connection *conn)
 {
        struct buffered_data *out, *tmp;
 
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index 258f6ff382..07d861d924 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -206,6 +206,7 @@ struct node *read_node(struct connection *conn, const void 
*ctx,
 
 struct connection *new_connection(const struct interface_funcs *funcs);
 struct connection *get_connection_by_id(unsigned int conn_id);
+void ignore_connection(struct connection *conn);
 void check_store(void);
 void corrupt(struct connection *conn, const char *fmt, ...);
 
diff --git a/tools/xenstore/xenstored_domain.c 
b/tools/xenstore/xenstored_domain.c
index 47e9107c14..d03c7d93a9 100644
--- a/tools/xenstore/xenstored_domain.c
+++ b/tools/xenstore/xenstored_domain.c
@@ -268,14 +268,7 @@ void check_domains(void)
                                domain->shutdown = true;
                                notify = 1;
                        }
-                       /*
-                        * On Restore, we may have been unable to remap the
-                        * interface and the port. As we don't know whether
-                        * this was because of a dying domain, we need to
-                        * check if the interface and port are still valid.
-                        */
-                       if (!dominfo.dying && domain->port &&
-                           domain->interface)
+                       if (!dominfo.dying)
                                continue;
                }
                if (domain->conn) {
@@ -1303,6 +1296,17 @@ void read_state_connection(const void *ctx, const void 
*state)
                if (!domain)
                        barf("domain allocation error");
 
+               conn = domain->conn;
+
+               /*
+                * We may not have been able to restore the domain (for
+                * instance because it revoked the Xenstore grant). We need
+                * to keep it around to send @releaseDomain when it is
+                * dead. So mark it as ignored.
+                */
+               if (!domain->port || !domain->interface)
+                       ignore_connection(conn);
+
                if (sc->spec.ring.tdomid != DOMID_INVALID) {
                        tdomain = find_or_alloc_domain(ctx,
                                                       sc->spec.ring.tdomid);
@@ -1311,7 +1315,6 @@ void read_state_connection(const void *ctx, const void 
*state)
                        talloc_reference(domain->conn, tdomain->conn);
                        domain->conn->target = tdomain->conn;
                }
-               conn = domain->conn;
        }
 
        conn->conn_id = sc->conn_id;
--
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