[Xen-changelog] [xen master] tools/libxl: Only continue stream operations if the stream is still in progress

[patchbot@xxxxxxx]

commit a636d4fc2f329566ddc1afff04d833281d8a07eb
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Jul 28 22:44:36 2015 +0100
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Wed Jul 29 15:24:50 2015 +0100

    tools/libxl: Only continue stream operations if the stream is still in 
progress
    
    Part of the callback contract with check_all_finished() is that each
    running parallel task shall call it exactly once.
    
    Previously, it was possible for stream_continue() or
    write_toolstack_record() to fail and call into check_all_finished().  As
    the save helpers callback has fired, it no longer counts as in use,
    which causes check_all_finished() to fire the stream callback.  Then,
    unwinding the stack back and calling check_all_finished() a second time
    results in the same conditions being observed, and the stream callback
    being fired a second time.
    
    To avoid this, check_all_finished() is called before any other actions
    which continue the stream functionality, and the stream is only
    continued if it has not been torn down.  This guarantees not to continue
    stream operations if the stream does not owe a callback to
    check_all_finished().
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
---
 tools/libxl/libxl_stream_read.c  |   20 ++++++++++++++------
 tools/libxl/libxl_stream_write.c |   11 +++++++++--
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/tools/libxl/libxl_stream_read.c b/tools/libxl/libxl_stream_read.c
index d54789c..fd3675c 100644
--- a/tools/libxl/libxl_stream_read.c
+++ b/tools/libxl/libxl_stream_read.c
@@ -738,14 +738,22 @@ void libxl__xc_domain_restore_done(libxl__egc *egc, void 
*dcs_void,
         goto err;
     }
 
-    /*
-     * Libxc has indicated that it is done with the stream.  Resume reading
-     * libxl records from it.
-     */
-    stream_continue(egc, stream);
-
  err:
     check_all_finished(egc, stream, rc);
+
+    /*
+     * This function is the callback associated with the save helper
+     * task, not the stream task.  We do not know whether the stream is
+     * alive, and check_all_finished() may have torn it down around us.
+     * If the stream is not still alive, we must not continue any work.
+     */
+    if (libxl__stream_read_inuse(stream)) {
+        /*
+         * Libxc has indicated that it is done with the stream.  Resume reading
+         * libxl records from it.
+         */
+        stream_continue(egc, stream);
+    }
 }
 
 static void conversion_done(libxl__egc *egc,
diff --git a/tools/libxl/libxl_stream_write.c b/tools/libxl/libxl_stream_write.c
index 676ad0a..9e9c998 100644
--- a/tools/libxl/libxl_stream_write.c
+++ b/tools/libxl/libxl_stream_write.c
@@ -275,10 +275,17 @@ void libxl__xc_domain_save_done(libxl__egc *egc, void 
*dss_void,
         goto err;
     }
 
-    write_toolstack_record(egc, stream);
-
  err:
     check_all_finished(egc, stream, rc);
+
+    /*
+     * This function is the callback associated with the save helper
+     * task, not the stream task.  We do not know whether the stream is
+     * alive, and check_all_finished() may have torn it down around us.
+     * If the stream is not still alive, we must not continue any work.
+     */
+    if (libxl__stream_write_inuse(stream))
+        write_toolstack_record(egc, stream);
 }
 
 static void write_toolstack_record(libxl__egc *egc,
--
generated by git-patchbot for /home/xen/git/xen.git#master

_______________________________________________
Xen-changelog mailing list
Xen-changelog@xxxxxxxxxxxxx
http://lists.xensource.com/xen-changelog