svn commit: r301914 - stable/10/sys/dev/hyperv/vmbus

[Sepherosa Ziehau]

Author: sephe
Date: Wed Jun 15 05:31:35 2016
New Revision: 301914
URL: https://svnweb.freebsd.org/changeset/base/301914

Log:
  MFC 296180,297634
  
  296180
      hyperv: Use proper fence function to keep store-load order for msgs
  
      sfence only makes sure about the store-store order, which is not
      sufficient here.  Use atomic_thread_fence_seq_cst() as suggested
      jhb and kib (a locked op in the nutshell, which should have the
  
      Reviewed by:        jhb, kib, Jun Su <junsu microsoft com>
      MFC after:  1 week
      Sponsored by:       Microsoft OSTC
      Differential Revision:      https://reviews.freebsd.org/D5436
  
  297634
      hyperv: Use mb() instead of atomic_thread_fence_seq_cst()
  
      Since atomic_thread_fence_seq_cst() will become compiler fence on UP kernel.
  
      Reviewed by:        kib, Dexuan Cui <decui microsoft com>
      MFC after:  1 week
      Sponsored by:       Microsoft OSTC
      Differential Revision:      https://reviews.freebsd.org/D5852

Modified:
  stable/10/sys/dev/hyperv/vmbus/hv_vmbus_drv_freebsd.c
Directory Properties:
  stable/10/   (props changed)

Modified: stable/10/sys/dev/hyperv/vmbus/hv_vmbus_drv_freebsd.c
==============================================================================
--- stable/10/sys/dev/hyperv/vmbus/hv_vmbus_drv_freebsd.c	Wed Jun 15 05:16:37 2016	(r301913)
+++ stable/10/sys/dev/hyperv/vmbus/hv_vmbus_drv_freebsd.c	Wed Jun 15 05:31:35 2016	(r301914)
@@ -116,8 +116,12 @@ handled:
 	     * message_pending and EOMing. Otherwise, the EOMing will
 	     * not deliver any more messages
 	     * since there is no empty slot
+	     *
+	     * NOTE:
+	     * mb() is used here, since atomic_thread_fence_seq_cst()
+	     * will become compler fence on UP kernel.
 	     */
-	    wmb();
+	    mb();
 
 	    if (msg->header.message_flags.u.message_pending) {
 			/*
@@ -186,8 +190,12 @@ hv_vmbus_isr(struct trapframe *frame)
 		 * message_pending and EOMing. Otherwise, the EOMing will
 		 * not deliver any more messages
 		 * since there is no empty slot
+		 *
+		 * NOTE:
+		 * mb() is used here, since atomic_thread_fence_seq_cst()
+		 * will become compler fence on UP kernel.
 		 */
-		wmb();
+		mb();
 
 		if (msg->header.message_flags.u.message_pending) {
 			/*