From: "Potyra, Stefan" <Stefan.Potyra@elektrobit.com>
Date: Thu, 13 Jun 2019 15:55:55 -0700
Subject: mm/mlock.c: mlockall error for flag MCL_ONFAULT
Git-commit: dedca63504a204dc8410d98883fdc16dffa8cb80
Patch-mainline: v5.2-rc5
References: bsc#1148527, VM Functionality

If mlockall() is called with only MCL_ONFAULT as flag, it removes any
previously applied lockings and does nothing else.

This behavior is counter-intuitive and doesn't match the Linux man page.

  For mlockall():

  EINVAL Unknown flags were specified or MCL_ONFAULT was specified
  without either MCL_FUTURE or MCL_CURRENT.

Consequently, return the error EINVAL, if only MCL_ONFAULT is passed.
That way, applications will at least detect that they are calling
mlockall() incorrectly.

Link: http://lkml.kernel.org/r/20190527075333.GA6339@er01809n.ebgroup.elektrobit.com
Fixes: b0f205c2a308 ("mm: mlock: add mlock flags to enable VM_LOCKONFAULT usage")
Signed-off-by: Stefan Potyra <Stefan.Potyra@elektrobit.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/mlock.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -794,7 +794,8 @@ SYSCALL_DEFINE1(mlockall, int, flags)
 	unsigned long lock_limit;
 	int ret;
 
-	if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT)))
+	if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT)) ||
+	    flags == MCL_ONFAULT)
 		return -EINVAL;
 
 	if (!can_do_mlock())