[PATCH] Clear the objhash before completing restart, but delay free until later

[Dan Smith <danms@xxxxxxxxxx>]

This patch causes the restart coordinator to clear the object hash
before releasing the restarted tasks.  It does this to make sure
that any objects being held exclusively by the hash are released
before the tasks start running again.

To avoid the overhead of actually freeing the object hash's structures
at the same time, this adds a queue to ckpt_obj_hash and pushes
the ckpt_obj structures there to be free()'d later during the cleanup
process.

Signed-off-by: Dan Smith <danms@xxxxxxxxxx>
---
 include/linux/checkpoint.h  |    1 +
 kernel/checkpoint/objhash.c |   20 +++++++++++++++++---
 kernel/checkpoint/restart.c |    2 ++
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index a11d40e..f888363 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -179,6 +179,7 @@ extern void restore_notify_error(struct ckpt_ctx *ctx);
 extern int ckpt_obj_module_get(void);
 extern void ckpt_obj_module_put(void);
 
+extern void ckpt_obj_hash_clear(struct ckpt_ctx *ctx);
 extern void ckpt_obj_hash_free(struct ckpt_ctx *ctx);
 extern int ckpt_obj_hash_alloc(struct ckpt_ctx *ctx);
 
diff --git a/kernel/checkpoint/objhash.c b/kernel/checkpoint/objhash.c
index 62c34ff..b62fe8d 100644
--- a/kernel/checkpoint/objhash.c
+++ b/kernel/checkpoint/objhash.c
@@ -27,6 +27,7 @@ struct ckpt_obj {
 	const struct ckpt_obj_ops *ops;
 	struct hlist_node hash;
 	struct hlist_node next;
+	struct list_head free;
 };
 
 /*` object internal flags */
@@ -36,6 +37,7 @@ struct ckpt_obj {
 struct ckpt_obj_hash {
 	struct hlist_head *head;
 	struct hlist_head list;
+	struct list_head free;
 	int next_free_objref;
 };
 
@@ -128,8 +130,9 @@ int ckpt_obj_module_get(void)
 #define CKPT_OBJ_HASH_NBITS  10
 #define CKPT_OBJ_HASH_TOTAL  (1UL << CKPT_OBJ_HASH_NBITS)
 
-static void obj_hash_clear(struct ckpt_obj_hash *obj_hash)
+void ckpt_obj_hash_clear(struct ckpt_ctx *ctx)
 {
+	struct ckpt_obj_hash *obj_hash = ctx->obj_hash;
 	struct hlist_head *h = obj_hash->head;
 	struct hlist_node *n, *t;
 	struct ckpt_obj *obj;
@@ -139,7 +142,9 @@ static void obj_hash_clear(struct ckpt_obj_hash *obj_hash)
 		hlist_for_each_entry_safe(obj, n, t, &h[i], hash) {
 			if (obj->ops->ref_drop)
 				obj->ops->ref_drop(obj->ptr, 1);
-			kfree(obj);
+			hlist_del(&obj->hash);
+			hlist_del(&obj->next);
+			list_add(&obj->free, &obj_hash->free);
 		}
 	}
 }
@@ -149,7 +154,13 @@ void ckpt_obj_hash_free(struct ckpt_ctx *ctx)
 	struct ckpt_obj_hash *obj_hash = ctx->obj_hash;
 
 	if (obj_hash) {
-		obj_hash_clear(obj_hash);
+		struct ckpt_obj *obj, *next;
+
+		ckpt_obj_hash_clear(ctx);
+
+		list_for_each_entry_safe(obj, next, &obj_hash->free, free)
+			kfree(obj);
+
 		kfree(obj_hash->head);
 		kfree(ctx->obj_hash);
 		ctx->obj_hash = NULL;
@@ -173,6 +184,7 @@ int ckpt_obj_hash_alloc(struct ckpt_ctx *ctx)
 	obj_hash->head = head;
 	obj_hash->next_free_objref = 1;
 	INIT_HLIST_HEAD(&obj_hash->list);
+	INIT_LIST_HEAD(&obj_hash->free);
 
 	ctx->obj_hash = obj_hash;
 	return 0;
@@ -260,6 +272,8 @@ static struct ckpt_obj *obj_new(struct ckpt_ctx *ctx, void *ptr,
 		i = hash_long((unsigned long) objref, CKPT_OBJ_HASH_NBITS);
 	}
 
+	INIT_LIST_HEAD(&obj->free);
+
 	ret = ops->ref_grab ? ops->ref_grab(obj->ptr) : 0;
 	if (ret < 0) {
 		kfree(obj);
diff --git a/kernel/checkpoint/restart.c b/kernel/checkpoint/restart.c
index 17270b8..f2241a9 100644
--- a/kernel/checkpoint/restart.c
+++ b/kernel/checkpoint/restart.c
@@ -1349,6 +1349,8 @@ static int do_restore_coord(struct ckpt_ctx *ctx, pid_t pid)
 	if (ret < 0)
 		ckpt_err(ctx, ret, "restart failed (coordinator)\n");
 
+	ckpt_obj_hash_clear(ctx);
+
 	if (ckpt_test_error(ctx)) {
 		destroy_descendants(ctx);
 		ret = ckpt_get_error(ctx);
-- 
1.7.2.2

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