[PATCH 046/109] mm: add kernel_mbind() helper; remove in-kernel call to syscall

[Dominik Brodowski]

Using the mm-internal kernel_mbind() helper allows us to get rid of the
mm-internal call to the sys_mbind() syscall.

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@xxxxxxxxxxxxxxxxxxxxxxxxxx

Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
---
 mm/mempolicy.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 7399ede02b5f..e4d7d4c0b253 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1336,9 +1336,9 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
 	return copy_to_user(mask, nodes_addr(*nodes), copy) ? -EFAULT : 0;
 }
 
-SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
-		unsigned long, mode, const unsigned long __user *, nmask,
-		unsigned long, maxnode, unsigned, flags)
+static long kernel_mbind(unsigned long start, unsigned long len,
+			 unsigned long mode, const unsigned long __user *nmask,
+			 unsigned long maxnode, unsigned int flags)
 {
 	nodemask_t nodes;
 	int err;
@@ -1357,6 +1357,13 @@ SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
 	return do_mbind(start, len, mode, mode_flags, &nodes, flags);
 }
 
+SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
+		unsigned long, mode, const unsigned long __user *, nmask,
+		unsigned long, maxnode, unsigned int, flags)
+{
+	return kernel_mbind(start, len, mode, nmask, maxnode, flags);
+}
+
 /* Set the process memory policy */
 SYSCALL_DEFINE3(set_mempolicy, int, mode, const unsigned long __user *, nmask,
 		unsigned long, maxnode)
@@ -1575,7 +1582,7 @@ COMPAT_SYSCALL_DEFINE6(mbind, compat_ulong_t, start, compat_ulong_t, len,
 			return -EFAULT;
 	}
 
-	return sys_mbind(start, len, mode, nm, nr_bits+1, flags);
+	return kernel_mbind(start, len, mode, nm, nr_bits+1, flags);
 }
 
 COMPAT_SYSCALL_DEFINE4(migrate_pages, compat_pid_t, pid,
-- 
2.16.3