vfs: patch for unpause()/revive() race condition

	. unpause() and revive() can race - revive() can run during
	  a device i/o unblock, causing two sendnb()s to occur, and the
	  2nd one to fail
	. this can easily happen when a process is blocking on tty and
	  is then killed by a signal - tty cancels the i/o and then
	  kills the process by a signal

Change-Id: Ia319acaedfa336b78c030a2c4af7246959bdcf87

diff --git a/servers/vfs/pipe.c b/servers/vfs/pipe.c
index f9a4cfb3c5d746d8d8b2066ac54d2f42a04c29f1..8f4fd703695b88d078a8224d75be738f57ba4eca 100644 (file)
--- a/servers/vfs/pipe.c
+++ b/servers/vfs/pipe.c
@@ -640,13 +640,14 @@ void unpause(endpoint_t proc_e)
                panic("VFS: unknown block reason: %d", blocked_on);
   }
 
-  rfp->fp_blocked_on = FP_BLOCKED_ON_NONE;
-
   if ((blocked_on == FP_BLOCKED_ON_PIPE || blocked_on == FP_BLOCKED_ON_POPEN)&&
        !wasreviving) {
        susp_count--;
   }
 
-  replycode(proc_e, status);   /* signal interrupted call */
+  if(rfp->fp_blocked_on != FP_BLOCKED_ON_NONE) {
+       rfp->fp_blocked_on = FP_BLOCKED_ON_NONE;
+       replycode(proc_e, status);      /* signal interrupted call */
+  }
 }