[Xen-changelog] [xen master] libxl: ao: Provide manip_refcnt

[patchbot@xxxxxxx]

commit bc0b4c80cb61583eba2fd99a21d6a4e337233818
Author:     Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
AuthorDate: Fri Dec 20 16:34:41 2013 +0000
Commit:     Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CommitDate: Fri Jun 26 16:53:50 2015 +0100

    libxl: ao: Provide manip_refcnt
    
    Previously we used in_initiator to stop the ao being freed while we
    were still in the initiator function (which would result in the
    initiator's call to libxl__ao_inprogress accessing the ao after it had
    been freed).
    
    We are going to introduce a new libxl entrypoint which finds, and
    operates on, ongoing aos.  This function needs the same protection,
    and might even end up running on the same ao multiple times
    concurrently.
    
    So do this with reference counting instead, with a new variable
    ao->manip_refcnt.
    
    We keep ao->in_initiator because that allows us to keep some useful
    asserts about the sequencing of libxl__ao_inprogress, etc.
    
    Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
    Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
    ---
    v5: Fix typo in commit message.
    v3: Add a missing space.
        Mention locking in the comment.
---
 tools/libxl/libxl_event.c    |   43 +++++++++++++++++++++++++++++++++--------
 tools/libxl/libxl_internal.h |    1 +
 2 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/tools/libxl/libxl_event.c b/tools/libxl/libxl_event.c
index 96efb33..6d5f9d8 100644
--- a/tools/libxl/libxl_event.c
+++ b/tools/libxl/libxl_event.c
@@ -33,6 +33,8 @@
 
 static libxl__ao *ao_nested_root(libxl__ao *ao);
 
+static void ao__check_destroy(libxl_ctx *ctx, libxl__ao *ao);
+
 
 /*
  * The counter osevent_in_hook is used to ensure that the application
@@ -1347,8 +1349,7 @@ static void egc_run_callbacks(libxl__egc *egc)
         ao->how.callback(CTX, ao->rc, ao->how.u.for_callback);
         CTX_LOCK;
         ao->notified = 1;
-        if (!ao->in_initiator)
-            libxl__ao__destroy(CTX, ao);
+        ao__check_destroy(CTX, ao);
         CTX_UNLOCK;
     }
 }
@@ -1729,6 +1730,33 @@ int libxl_event_wait(libxl_ctx *ctx, libxl_event 
**event_r,
  *                              - destroy the ao
  */
 
+
+/*
+ * A "manip" is a libxl public function manipulating this ao, which
+ * has a pointer to it.  We have to not destroy it while that's the
+ * case, obviously.  Callers must have the ctx locked, obviously.
+ */
+static void ao__manip_enter(libxl__ao *ao)
+{
+    assert(ao->manip_refcnt < INT_MAX);
+    ao->manip_refcnt++;
+}
+
+static void ao__manip_leave(libxl_ctx *ctx, libxl__ao *ao)
+{
+    assert(ao->manip_refcnt > 0);
+    ao->manip_refcnt--;
+    ao__check_destroy(ctx, ao);
+}
+
+static void ao__check_destroy(libxl_ctx *ctx, libxl__ao *ao)
+{
+    if (!ao->manip_refcnt && ao->notified) {
+        assert(ao->complete);
+        libxl__ao__destroy(ctx, ao);
+    }
+}
+
 void libxl__ao__destroy(libxl_ctx *ctx, libxl__ao *ao)
 {
     AO_GC;
@@ -1810,8 +1838,8 @@ void libxl__ao_complete_check_progress_reports(libxl__egc 
*egc, libxl__ao *ao)
         }
         ao->notified = 1;
     }
-    if (!ao->in_initiator && ao->notified)
-        libxl__ao__destroy(ctx, ao);
+    
+    ao__check_destroy(ctx, ao);
 }
 
 libxl__ao *libxl__ao_create(libxl_ctx *ctx, uint32_t domid,
@@ -1826,6 +1854,7 @@ libxl__ao *libxl__ao_create(libxl_ctx *ctx, uint32_t 
domid,
     ao->magic = LIBXL__AO_MAGIC;
     ao->constructing = 1;
     ao->in_initiator = 1;
+    ao__manip_enter(ao);
     ao->poller = 0;
     ao->domid = domid;
     LIBXL_INIT_GC(ao->gc, ctx);
@@ -1906,11 +1935,7 @@ int libxl__ao_inprogress(libxl__ao *ao,
     }
 
     ao->in_initiator = 0;
-
-    if (ao->notified) {
-        assert(ao->complete);
-        libxl__ao__destroy(CTX,ao);
-    }
+    ao__manip_leave(CTX, ao);
 
     return rc;
 }
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 79cdec1..02314b6 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -469,6 +469,7 @@ struct libxl__ao {
      */
     uint32_t magic;
     unsigned constructing:1, in_initiator:1, complete:1, notified:1;
+    int manip_refcnt;
     libxl__ao *nested_root;
     int nested_progeny;
     int progress_reports_outstanding;
--
generated by git-patchbot for /home/xen/git/xen.git#master

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