File 5537a81d-libxl-fd-events3.patch of Package xen.11298

Referencs: bsc#955104 bsc#959552 bsc#993665 bsc#959330 bsc#990500

commit 56d2350bf542ad5fd20d20e4e9dac76e8d9a54fe
Author: Ian Jackson <ian.jackson@eu.citrix.com>
Date:   Thu Apr 16 19:23:28 2015 +0100

    libxl: fd events: Suppress spurious fd events
    
    Always recheck with poll() right before making the callback.
    
    All sorts of things may have happened since poll() originally signaled
    the fd.  We would like the main functional libxl code not to have to
    worry about spurious wakeups.
    
    In particular, this fixes a bug in the save/restore callout: the save
    helper message reader operates with the fd in blocking mode.  In a
    multithreaded program one thread might have eaten all the messages out
    of the fd while another one is busy returning from poll and reacquiring
    the libxl lock, possibly resulting in a deadlock.
    
    (Also, we abolish the anomalous direct caller of efd->func.)
    
    Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Reported-by: Jim Fehlig <jfehlig@suse.com>
    Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
    CC: Jim Fehlig <jfehlig@suse.com>
    CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Tested-by: Jim Fehlig <jfehlig@suse.com>
    Acked-by: Ian Campbell <ian.campbell@citrix.com>

Index: xen-4.5.3-testing/tools/libxl/libxl_event.c
===================================================================
--- xen-4.5.3-testing.orig/tools/libxl/libxl_event.c
+++ xen-4.5.3-testing/tools/libxl/libxl_event.c
@@ -1127,12 +1127,15 @@ static int afterpoll_check_fd(libxl__pol
     return revents;
 }
 
-static void fd_occurs(libxl__egc *egc, libxl__ev_fd *efd, short revents)
+static void fd_occurs(libxl__egc *egc, libxl__ev_fd *efd, short revents_ign)
 {
-    DBG("ev_fd=%p occurs fd=%d events=%x revents=%x",
-        efd, efd->fd, efd->events, revents);
+    short revents_current = libxl__fd_poll_recheck(egc, efd->fd, efd->events);
 
-    efd->func(egc, efd, efd->fd, efd->events, revents);
+    DBG("ev_fd=%p occurs fd=%d events=%x revents_ign=%x revents_current=%x",
+        efd, efd->fd, efd->events, revents_ign, revents_current);
+
+    if (revents_current)
+        efd->func(egc, efd, efd->fd, efd->events, revents_current);
 }
 
 static void afterpoll_internal(libxl__egc *egc, libxl__poller *poller,
@@ -1261,10 +1264,7 @@ void libxl_osevent_occurred_fd(libxl_ctx
     if (!ev) goto out;
     if (ev->fd != fd) goto out;
 
-    short current_revents = libxl__fd_poll_recheck(egc, ev->fd, ev->events);
-
-    if (current_revents)
-        ev->func(egc, ev, fd, ev->events, current_revents);
+    fd_occurs(egc, ev, revents_ign);
 
  out:
     CTX_UNLOCK;
Index: xen-4.5.3-testing/tools/libxl/libxl_internal.h
===================================================================
--- xen-4.5.3-testing.orig/tools/libxl/libxl_internal.h
+++ xen-4.5.3-testing/tools/libxl/libxl_internal.h
@@ -162,6 +162,9 @@ typedef void libxl__ev_fd_callback(libxl
    *
    * It is not permitted to listen for the same or overlapping events
    * on the same fd using multiple different libxl__ev_fd's.
+   *
+   * (Spurious wakeups, and spurious bits set in revents, are
+   * suppressed by the libxl event core.)
    */
 struct libxl__ev_fd {
     /* caller should include this in their own struct */