hugetlb: add locking for overcommit sysctl

When I replaced hugetlb_dynamic_pool with nr_overcommit_hugepages I used
proc_doulongvec_minmax() directly.  However, hugetlb.c's locking rules
require that all counter modifications occur under the hugetlb_lock.  Add a
callback into the hugetlb code similar to the one for nr_hugepages.  Grab
the lock around the manipulation of nr_overcommit_hugepages in
proc_doulongvec_minmax().

Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Acked-by: Adam Litke <agl@us.ibm.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: William Lee Irwin III <wli@holomorphy.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 12 insertions, 1 deletions

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 30d606afcafe..7ca198b379af 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -17,6 +17,7 @@ static inline int is_vm_hugetlb_page(struct vm_area_struct *vma)
 }
 
 int hugetlb_sysctl_handler(struct ctl_table *, int, struct file *, void __user *, size_t *, loff_t *);
+int hugetlb_overcommit_handler(struct ctl_table *, int, struct file *, void __user *, size_t *, loff_t *);
 int hugetlb_treat_movable_handler(struct ctl_table *, int, struct file *, void __user *, size_t *, loff_t *);
 int copy_hugetlb_page_range(struct mm_struct *, struct mm_struct *, struct vm_area_struct *);
 int follow_hugetlb_page(struct mm_struct *, struct vm_area_struct *, struct page **, struct vm_area_struct **, unsigned long *, int *, int, int);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8c98d8147d88..9dadc9d88a03 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -982,7 +982,7 @@ static struct ctl_table vm_table[] = {
                 .data           = &nr_overcommit_huge_pages,
                 .maxlen         = sizeof(nr_overcommit_huge_pages),
                 .mode           = 0644,
-                .proc_handler   = &proc_doulongvec_minmax,
+                .proc_handler   = &hugetlb_overcommit_handler,
         },
 #endif
         {
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 1a5642074e34..d9a380312467 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -605,6 +605,16 @@ int hugetlb_treat_movable_handler(struct ctl_table *table, int write,
         return 0;
 }
 
+int hugetlb_overcommit_handler(struct ctl_table *table, int write,
+                        struct file *file, void __user *buffer,
+                        size_t *length, loff_t *ppos)
+{
+        spin_lock(&hugetlb_lock);
+        proc_doulongvec_minmax(table, write, file, buffer, length, ppos);
+        spin_unlock(&hugetlb_lock);
+        return 0;
+}
+
 #endif /* CONFIG_SYSCTL */
 
 int hugetlb_report_meminfo(char *buf)