mm: fix division by 0 in percpu_pagelist_fraction()

percpu_pagelist_fraction_sysctl_handler() has only considered -EINVAL as
a possible error from proc_dointvec_minmax().

If any other error is returned, it would proceed to divide by zero since
percpu_pagelist_fraction wasn't getting initialized at any point.  For
example, writing 0 bytes into the proc file would trigger the issue.
Signed-off-by: NSasha Levin <levinsasha928@gmail.com>
Reviewed-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -105,7 +105,7 @@ unsigned long totalreserve_pages __read_mostly;
  */
 unsigned long dirty_balance_reserve __read_mostly;
 
-int percpu_pagelist_fraction;
+int percpu_pagelist_fraction = 8;
 gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
 
 #ifdef CONFIG_PM_SLEEP
@@ -5203,7 +5203,7 @@ int percpu_pagelist_fraction_sysctl_handler(ctl_table *table, int write,
 	int ret;
 
 	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
-	if (!write || (ret == -EINVAL))
+	if (!write || (ret < 0))
 		return ret;
 	for_each_populated_zone(zone) {
 		for_each_possible_cpu(cpu) {