Linux 3.7 compat, schedule_delayed_work()

Linux kernel commit d8e794d accidentally broke the delayed work
APIs for non-GPL callers.   While the APIs to schedule a delayed
work item are still available to all callers, it is no longer
possible to initialize the delayed work item.

I'm cautiously optimistic we could get the delayed_work_timer_fn
exported for all callers in the upstream kernel.  But frankly
the compatibility code to use this kernel interface has always
been problematic.

Therefore, this patch abandons direct use the of the Linux
kernel interface in favor of the new delayed taskq interface.
It provides roughly the same functionality as delayed work queues
but it's a stable interface under our control.

Signed-off-by: Brian Behlendorf <[email protected]>
Closes #1053

2 files changed, 21 insertions, 12 deletions

diff --git a/include/sys/zfs_ctldir.h b/include/sys/zfs_ctldir.h
index 0a3c142eb..1ff23a298 100644
--- a/include/sys/zfs_ctldir.h
+++ b/include/sys/zfs_ctldir.h
@@ -50,7 +50,7 @@ typedef struct {
 	char			*se_name;
 	char			*se_path;
 	struct inode		*se_inode;
-	struct delayed_work	se_work;
+	taskqid_t		se_taskqid;
 	avl_node_t		se_node;
 } zfs_snapentry_t;
 
diff --git a/module/zfs/zfs_ctldir.c b/module/zfs/zfs_ctldir.c
index d139b8613..a667340c8 100644
--- a/module/zfs/zfs_ctldir.c
+++ b/module/zfs/zfs_ctldir.c
@@ -90,6 +90,11 @@
  */
 int zfs_expire_snapshot = ZFSCTL_EXPIRE_SNAPSHOT;
 
+/*
+ * Dedicated task queue for unmounting snapshots.
+ */
+static taskq_t *zfs_expire_taskq;
+
 static zfs_snapentry_t *
 zfsctl_sep_alloc(void)
 {
@@ -112,16 +117,15 @@ zfsctl_sep_free(zfs_snapentry_t *sep)
 static void
 zfsctl_expire_snapshot(void *data)
 {
-	zfs_snapentry_t *sep;
-	zfs_sb_t *zsb;
+	zfs_snapentry_t *sep = (zfs_snapentry_t *)data;
+	zfs_sb_t *zsb = ITOZSB(sep->se_inode);
 	int error;
 
-	sep = spl_get_work_data(data, zfs_snapentry_t, se_work.work);
-	zsb = ITOZSB(sep->se_inode);
-
 	error = zfsctl_unmount_snapshot(zsb, sep->se_name, MNT_EXPIRE);
 	if (error == EBUSY)
-		schedule_delayed_work(&sep->se_work, zfs_expire_snapshot * HZ);
+		sep->se_taskqid = taskq_dispatch_delay(zfs_expire_taskq,
+		    zfsctl_expire_snapshot, sep, TQ_SLEEP,
+		    ddi_get_lbolt() + zfs_expire_snapshot * HZ);
 }
 
 int
@@ -661,7 +665,7 @@ zfsctl_snapdir_inactive(struct inode *ip)
 
 		if (sep->se_inode == ip) {
 			avl_remove(&zsb->z_ctldir_snaps, sep);
-			cancel_delayed_work_sync(&sep->se_work);
+			taskq_cancel_id(zfs_expire_taskq, sep->se_taskqid);
 			zfsctl_sep_free(sep);
 			break;
 		}
@@ -708,7 +712,8 @@ __zfsctl_unmount_snapshot(zfs_snapentry_t *sep, int flags)
 	 * to prevent zfsctl_expire_snapshot() from attempting a unmount.
 	 */
 	if ((error == 0) && !(flags & MNT_EXPIRE))
-		cancel_delayed_work(&sep->se_work);
+		taskq_cancel_id(zfs_expire_taskq, sep->se_taskqid);
+
 
 	return (error);
 }
@@ -837,7 +842,7 @@ zfsctl_mount_snapshot(struct path *path, int flags)
 	sep = avl_find(&zsb->z_ctldir_snaps, &search, NULL);
 	if (sep) {
 		avl_remove(&zsb->z_ctldir_snaps, sep);
-		cancel_delayed_work_sync(&sep->se_work);
+		taskq_cancel_id(zfs_expire_taskq, sep->se_taskqid);
 		zfsctl_sep_free(sep);
 	}
 
@@ -847,8 +852,9 @@ zfsctl_mount_snapshot(struct path *path, int flags)
 	sep->se_inode = ip;
 	avl_add(&zsb->z_ctldir_snaps, sep);
 
-        spl_init_delayed_work(&sep->se_work, zfsctl_expire_snapshot, sep);
-	schedule_delayed_work(&sep->se_work, zfs_expire_snapshot * HZ);
+	sep->se_taskqid = taskq_dispatch_delay(zfs_expire_taskq,
+	    zfsctl_expire_snapshot, sep, TQ_SLEEP,
+	    ddi_get_lbolt() + zfs_expire_snapshot * HZ);
 
 	mutex_exit(&zsb->z_ctldir_lock);
 error:
@@ -977,6 +983,8 @@ zfsctl_shares_lookup(struct inode *dip, char *name, struct inode **ipp,
 void
 zfsctl_init(void)
 {
+	zfs_expire_taskq = taskq_create("z_unmount", 1, maxclsyspri,
+	    1, 8, TASKQ_PREPOPULATE);
 }
 
 /*
@@ -986,6 +994,7 @@ zfsctl_init(void)
 void
 zfsctl_fini(void)
 {
+	taskq_destroy(zfs_expire_taskq);
 }
 
 module_param(zfs_expire_snapshot, int, 0644);