fs/namespace: convert devname allocation to kstrdup_const

VFS frequently performs duplication of strings located in read-only memory
section.  Replacing kstrdup by kstrdup_const allows to avoid such
operations.
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Greg KH <greg@kroah.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/namespace.c

@@ -201,7 +201,7 @@ static struct mount *alloc_vfsmnt(const char *name)
 			goto out_free_cache;
 
 		if (name) {
-			mnt->mnt_devname = kstrdup(name, GFP_KERNEL);
+			mnt->mnt_devname = kstrdup_const(name, GFP_KERNEL);
 			if (!mnt->mnt_devname)
 				goto out_free_id;
 		}
@@ -234,7 +234,7 @@ static struct mount *alloc_vfsmnt(const char *name)
 
 #ifdef CONFIG_SMP
 out_free_devname:
-	kfree(mnt->mnt_devname);
+	kfree_const(mnt->mnt_devname);
 #endif
 out_free_id:
 	mnt_free_id(mnt);
@@ -568,7 +568,7 @@ int sb_prepare_remount_readonly(struct super_block *sb)
 
 static void free_vfsmnt(struct mount *mnt)
 {
-	kfree(mnt->mnt_devname);
+	kfree_const(mnt->mnt_devname);
 #ifdef CONFIG_SMP
 	free_percpu(mnt->mnt_pcp);
 #endif