svn commit: r289511 - stable/10/sys/geom

[Edward Tomasz Napierala]

Author: trasz
Date: Sun Oct 18 14:34:13 2015
New Revision: 289511
URL: https://svnweb.freebsd.org/changeset/base/289511

Log:
  MFC r286237:
  
  Fix panic that would happen on forcibly unmounting devfs (note that
  as it is now, devfs ignores MNT_FORCE anyway, so it needs to be modified
  to trigger the panic) with consumers still opened.
  
  Note that this still results in a leak of r/w/e counters.  It seems
  to be harmless, though.  If anyone knows a better way to approach
  this - please tell.
  
  Sponsored by:	The FreeBSD Foundation

Modified:
  stable/10/sys/geom/geom_dev.c
Directory Properties:
  stable/10/   (props changed)

Modified: stable/10/sys/geom/geom_dev.c
==============================================================================
--- stable/10/sys/geom/geom_dev.c	Sun Oct 18 14:31:54 2015	(r289510)
+++ stable/10/sys/geom/geom_dev.c	Sun Oct 18 14:34:13 2015	(r289511)
@@ -399,6 +399,20 @@ g_dev_close(struct cdev *dev, int flags,
 #else
 	e = 0;
 #endif
+
+	/*
+	 * The vgonel(9) - caused by eg. forced unmount of devfs - calls
+	 * VOP_CLOSE(9) on devfs vnode without any FREAD or FWRITE flags,
+	 * which would result in zero deltas, which in turn would cause
+	 * panic in g_access(9).
+	 *
+	 * Note that we cannot zero the counters (ie. do "r = cp->acr"
+	 * etc) instead, because the consumer might be opened in another
+	 * devfs instance.
+	 */
+	if (r + w + e == 0)
+		return (EINVAL);
+
 	sc = cp->private;
 	mtx_lock(&sc->sc_mtx);
 	sc->sc_open += r + w + e;