linux-kernel - [PATCH] mm: don't overwrite mm->def_flags in do

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Message-Id: <1360165774-55458-1-git-send-email-gerald.schaefer@de.ibm.com>
Date:	Wed,  6 Feb 2013 16:49:34 +0100
From:	Gerald Schaefer <gerald.schaefer@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Vivek Goyal <vgoyal@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>
Subject: [PATCH] mm: don't overwrite mm->def_flags in do_mlockall()

With commit 8e72033 "thp: make MADV_HUGEPAGE check for mm->def_flags"
the VM_NOHUGEPAGE flag may be set on s390 in mm->def_flags for certain
processes, to prevent future thp mappings. This would be overwritten
by do_mlockall(), which sets it back to 0 with an optional VM_LOCKED
flag set.

To fix this, instead of overwriting mm->def_flags in do_mlockall(),
only the VM_LOCKED flag should be set or cleared.

Reported-by: Vivek Goyal <vgoyal@...hat.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@...ibm.com>
---
 mm/mlock.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index f0b9ce5..c9bd528 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -517,11 +517,11 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
 static int do_mlockall(int flags)
 {
 	struct vm_area_struct * vma, * prev = NULL;
-	unsigned int def_flags = 0;
 
 	if (flags & MCL_FUTURE)
-		def_flags = VM_LOCKED;
-	current->mm->def_flags = def_flags;
+		current->mm->def_flags |= VM_LOCKED;
+	else
+		current->mm->def_flags &= ~VM_LOCKED;
 	if (flags == MCL_FUTURE)
 		goto out;
 
-- 
1.7.12.4

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