We will use percpu-refcount to serialize against concurrent swapoff. This
patch adds the percpu_ref support for swap.
Signed-off-by: Miaohe Lin <linmia...@huawei.com>
---
include/linux/swap.h | 3 +++
mm/swapfile.c | 33 +++++++++++++++++++++++++++++----
2 files changed, 32 insertions(+), 4 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 144727041e78..8be36eb58b7a 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -240,6 +240,7 @@ struct swap_cluster_list {
* The in-memory structure used to track swap areas.
*/
struct swap_info_struct {
+ struct percpu_ref users; /* serialization against concurrent
swapoff */
unsigned long flags; /* SWP_USED etc: see above */
signed short prio; /* swap priority of this type */
struct plist_node list; /* entry in swap_active_head */
@@ -260,6 +261,8 @@ struct swap_info_struct {
struct block_device *bdev; /* swap device or bdev of swap file */
struct file *swap_file; /* seldom referenced */
unsigned int old_block_size; /* seldom referenced */
+ bool ref_initialized; /* seldom referenced */
+ struct completion comp; /* seldom referenced */
#ifdef CONFIG_FRONTSWAP
unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
atomic_t frontswap_pages; /* frontswap pages in-use counter */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 149e77454e3c..66515a3a2824 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -39,6 +39,7 @@
#include <linux/export.h>
#include <linux/swap_slots.h>
#include <linux/sort.h>
+#include <linux/completion.h>
#include <asm/tlbflush.h>
#include <linux/swapops.h>
@@ -511,6 +512,14 @@ static void swap_discard_work(struct work_struct *work)
spin_unlock(&si->lock);
}
+static void swap_users_ref_free(struct percpu_ref *ref)
+{
+ struct swap_info_struct *si;
+
+ si = container_of(ref, struct swap_info_struct, users);
+ complete(&si->comp);
+}
+
static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
{
struct swap_cluster_info *ci = si->cluster_info;
@@ -2500,7 +2509,7 @@ static void enable_swap_info(struct swap_info_struct *p,
int prio,
* Guarantee swap_map, cluster_info, etc. fields are valid
* between get/put_swap_device() if SWP_VALID bit is set
*/
- synchronize_rcu();
+ percpu_ref_resurrect(&p->users);
spin_lock(&swap_lock);
spin_lock(&p->lock);
_enable_swap_info(p);
@@ -2621,11 +2630,18 @@ SYSCALL_DEFINE1(swapoff, const char __user *,
specialfile)
p->flags &= ~SWP_VALID; /* mark swap device as invalid */
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
+
+ percpu_ref_kill(&p->users);
/*
- * wait for swap operations protected by get/put_swap_device()
- * to complete
+ * We need synchronize_rcu() here to protect the accessing
+ * to the swap cache data structure.
*/
synchronize_rcu();
+ /*
+ * Wait for swap operations protected by get/put_swap_device()
+ * to complete.
+ */
+ wait_for_completion(&p->comp);
flush_work(&p->discard_work);
@@ -3132,7 +3148,7 @@ static bool swap_discardable(struct swap_info_struct *si)
SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
{
struct swap_info_struct *p;
- struct filename *name;
+ struct filename *name = NULL;
struct file *swap_file = NULL;
struct address_space *mapping;
int prio;
@@ -3163,6 +3179,15 @@ SYSCALL_DEFINE2(swapon, const char __user *,
specialfile, int, swap_flags)
INIT_WORK(&p->discard_work, swap_discard_work);
+ if (!p->ref_initialized) {
+ error = percpu_ref_init(&p->users, swap_users_ref_free,
+ PERCPU_REF_INIT_DEAD, GFP_KERNEL);
+ if (unlikely(error))
+ goto bad_swap;
+ init_completion(&p->comp);
+ p->ref_initialized = true;
+ }
+
name = getname(specialfile);
if (IS_ERR(name)) {
error = PTR_ERR(name);
--
2.19.1
