svn commit: r285208 - head/sys/kern

[Patrick Kelsey]

Author: pkelsey
Date: Mon Jul  6 16:07:21 2015
New Revision: 285208
URL: https://svnweb.freebsd.org/changeset/base/285208

Log:
  Don't acquire sysctlmemlock in userland_sysctl() when the old value
  pointer is NULL, as in that case there are no userland pages that
  could potentially be wired.  It is common for old to be NULL and
  oldlenp to be non-NULL in calls to userland_sysctl(), as this is used
  to probe for the length of a variable-length sysctl entry before
  retrieving a value.  Note that it is typical for such calls to be made
  with an uninitialized value in *oldlenp, so sysctlmemlock was
  essentially being acquired at random (depending on the uninitialized
  value in *oldlenp being > PAGE_SIZE or not) for these calls prior to
  this patch.
  
  Differential Revision: https://reviews.freebsd.org/D2987
  Reviewed by: mjg, kib
  Approved by: jmallett (mentor)
  MFC after: 1 month

Modified:
  head/sys/kern/kern_sysctl.c

Modified: head/sys/kern/kern_sysctl.c
==============================================================================
--- head/sys/kern/kern_sysctl.c	Mon Jul  6 14:09:00 2015	(r285207)
+++ head/sys/kern/kern_sysctl.c	Mon Jul  6 16:07:21 2015	(r285208)
@@ -1784,7 +1784,7 @@ userland_sysctl(struct thread *td, int *
 		ktrsysctl(name, namelen);
 #endif
 
-	if (req.oldlen > PAGE_SIZE) {
+	if (req.oldptr && req.oldlen > PAGE_SIZE) {
 		memlocked = 1;
 		sx_xlock(&sysctlmemlock);
 	} else