[PATCH v2] mm: mlockall error for flag MCL_ONFAULT

From: Potyra, Stefan
Date: Mon May 27 2019 - 04:15:39 EST


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 withâ
out 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.

Fixes: b0f205c2a308 ("mm: mlock: add mlock flags to enable VM_LOCKONFAULT usage")
Signed-off-by: Stefan Potyra <Stefan.Potyra@xxxxxxxxxxxxxx>
Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
---
mm/mlock.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index e492a155c51a..03f39cbdd4c4 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -797,7 +797,8 @@ 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())
--
2.20.1