[RFC] mm: prevent set a value less than 0 to min_free_kbytes

[Han Pingtian <hanpt@linux.vnet.ibm.com>]

If echo -1 > /proc/vm/sys/min_free_kbytes, the system will hang.
Changing proc_dointvec() to proc_dointvec_minmax() in the
min_free_kbytes_sysctl_handler() can prevent this to happen.

Signed-off-by: Han Pingtian <hanpt@linux.vnet.ibm.com>
---
 mm/page_alloc.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 77937e0..a9dcfd8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5692,7 +5692,12 @@ module_init(init_per_zone_wmark_min)
 int min_free_kbytes_sysctl_handler(ctl_table *table, int write,
 	void __user *buffer, size_t *length, loff_t *ppos)
 {
-	proc_dointvec(table, write, buffer, length, ppos);
+	int rc;
+
+	rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
+	if (rc)
+		return rc;
+
 	if (write) {
 		user_min_free_kbytes = min_free_kbytes;
 		setup_per_zone_wmarks();
-- 
1.7.7.6

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