Commit 74a31df4 authored by Xiubo Li's avatar Xiubo Li Committed by Ilya Dryomov
Browse files

ceph: eliminate the recursion when rebuilding the snap context 



Use a list instead of recursion to avoid possible stack overflow.

Signed-off-by: default avatarXiubo Li <xiubli@redhat.com>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
parent 2e586641

fs/ceph/snap.c

+48 −9
Original line number Diff line number Diff line
@@ -127,6 +127,7 @@ static struct ceph_snap_realm *ceph_create_snap_realm( 
	INIT_LIST_HEAD(&realm->child_item);

	INIT_LIST_HEAD(&realm->empty_item);

	INIT_LIST_HEAD(&realm->dirty_item);

	INIT_LIST_HEAD(&realm->rebuild_item);

	INIT_LIST_HEAD(&realm->inodes_with_caps);

	spin_lock_init(&realm->inodes_with_caps_lock);

	__insert_snap_realm(&mdsc->snap_realms, realm);
@@ -320,6 +321,7 @@ static int cmpu64_rev(const void *a, const void *b) 
 * build the snap context for a given realm.

 */

static int build_snap_context(struct ceph_snap_realm *realm,

			      struct list_head *realm_queue,

			      struct list_head *dirty_realms)

{

	struct ceph_snap_realm *parent = realm->parent;
@@ -334,9 +336,9 @@ static int build_snap_context(struct ceph_snap_realm *realm, 
	 */

	if (parent) {

		if (!parent->cached_context) {

			err = build_snap_context(parent, dirty_realms);

			if (err)

				goto fail;

			/* add to the queue head */

			list_add(&parent->rebuild_item, realm_queue);

			return 1;

		}

		num += parent->cached_context->num_snaps;

	}
@@ -420,13 +422,50 @@ static int build_snap_context(struct ceph_snap_realm *realm, 
static void rebuild_snap_realms(struct ceph_snap_realm *realm,

				struct list_head *dirty_realms)

{

	struct ceph_snap_realm *child;

	LIST_HEAD(realm_queue);

	int last = 0;

	bool skip = false;



	list_add_tail(&realm->rebuild_item, &realm_queue);



	while (!list_empty(&realm_queue)) {

		struct ceph_snap_realm *_realm, *child;



		_realm = list_first_entry(&realm_queue,

					  struct ceph_snap_realm,

					  rebuild_item);



	dout("rebuild_snap_realms %llx %p\n", realm->ino, realm);

	build_snap_context(realm, dirty_realms);

		/*

		 * If the last building failed dues to memory

		 * issue, just empty the realm_queue and return

		 * to avoid infinite loop.

		 */

		if (last < 0) {

			list_del_init(&_realm->rebuild_item);

			continue;

		}



	list_for_each_entry(child, &realm->children, child_item)

		rebuild_snap_realms(child, dirty_realms);

		last = build_snap_context(_realm, &realm_queue, dirty_realms);

		dout("rebuild_snap_realms %llx %p, %s\n", _realm->ino, _realm,

		     last > 0 ? "is deferred" : !last ? "succeeded" : "failed");



		/* is any child in the list ? */

		list_for_each_entry(child, &_realm->children, child_item) {

			if (!list_empty(&child->rebuild_item)) {

				skip = true;

				break;

			}

		}



		if (!skip) {

			list_for_each_entry(child, &_realm->children, child_item)

				list_add_tail(&child->rebuild_item, &realm_queue);

		}



		/* last == 1 means need to build parent first */

		if (last <= 0)

			list_del_init(&_realm->rebuild_item);

	}

}

fs/ceph/super.h

+2 −0
Original line number Diff line number Diff line
@@ -883,6 +883,8 @@ struct ceph_snap_realm { 


	struct list_head dirty_item;     /* if realm needs new context */



	struct list_head rebuild_item;   /* rebuild snap realms _downward_ in hierarchy */



	/* the current set of snaps for this realm */

	struct ceph_snap_context *cached_context;