mm/compaction: really limit compact_unevictable_allowed to 0 and 1

The proc file `compact_unevictable_allowed' should allow 0 and 1 only, the
`extra*' attribues have been set properly but without
proc_dointvec_minmax() as the `proc_handler' the limit will not be
enforced.

Use proc_dointvec_minmax() as the `proc_handler' to enfoce the valid
specified range.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Link: http://lkml.kernel.org/r/20200303202054.gsosv7fsx2ma3cic@linutronix.deSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sysctl.c

@@ -1467,7 +1467,7 @@ static struct ctl_table vm_table[] = {
 		.data		= &sysctl_compact_unevictable_allowed,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_ONE,
 	},