mm: fix dirty_bytes/dirty_background_bytes sysctls on 64bit arches

We need to pass an unsigned long as the minimum, because it gets casted
to an unsigned long in the sysctl handler. If we pass an int, we'll
access four more bytes on 64bit arches, resulting in a random minimum
value.

[rientjes@google.com: fix type of `old_bytes']
Signed-off-by: Sven Wegener <sven.wegener@stealer.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 4 insertions, 3 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 790f9d785663..c5ef44ff850f 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -101,6 +101,7 @@ static int two = 2;
 
 static int zero;
 static int one = 1;
+static unsigned long one_ul = 1;
 static int one_hundred = 100;
 
 /* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
@@ -974,7 +975,7 @@ static struct ctl_table vm_table[] = {
                 .mode           = 0644,
                 .proc_handler   = &dirty_background_bytes_handler,
                 .strategy       = &sysctl_intvec,
-                .extra1         = &one,
+                .extra1         = &one_ul,
         },
         {
                 .ctl_name       = VM_DIRTY_RATIO,
@@ -995,7 +996,7 @@ static struct ctl_table vm_table[] = {
                 .mode           = 0644,
                 .proc_handler   = &dirty_bytes_handler,
                 .strategy       = &sysctl_intvec,
-                .extra1         = &one,
+                .extra1         = &one_ul,
         },
         {
                 .procname       = "dirty_writeback_centisecs",
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index dc32dae01e5f..c17005e73974 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -209,7 +209,7 @@ int dirty_bytes_handler(struct ctl_table *table, int write,
                 struct file *filp, void __user *buffer, size_t *lenp,
                 loff_t *ppos)
 {
-        int old_bytes = vm_dirty_bytes;
+        unsigned long old_bytes = vm_dirty_bytes;
         int ret;
 
         ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);