linux-kernel - [PATCH v2] mm: mlockall error for flag MCL

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Message-ID: <20190527075333.GA6339@er01809n.ebgroup.elektrobit.com>
Date:   Mon, 27 May 2019 07:53:42 +0000
From:   "Potyra, Stefan" <Stefan.Potyra@...ktrobit.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Daniel Jordan <daniel.m.jordan@...cle.com>
CC:     "Potyra, Stefan" <Stefan.Potyra@...ktrobit.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Jordan, Tobias" <Tobias.Jordan@...ktrobit.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: [PATCH v2] mm: mlockall error for flag MCL_ONFAULT

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 with‐
         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@...ktrobit.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@...cle.com>
Acked-by: Michal Hocko <mhocko@...e.com>
---
 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