md: use sysfs_notify_dirent to notify changes to md/dev-xxx/state

The 'state' file for a device reports, for example, when the device
has failed.  Changes should be reported to userspace ASAP without
the possibility of blocking on low-memory.  sysfs_notify does
have that possibility (as it takes a mutex which can be held
across a kmalloc) so use sysfs_notify_dirent instead.
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/md.c

@@ -1462,6 +1462,8 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
 		kobject_del(&rdev->kobj);
 		goto fail;
 	}
+	rdev->sysfs_state = sysfs_get_dirent(rdev->kobj.sd, "state");
+
 	list_add_rcu(&rdev->same_set, &mddev->disks);
 	bd_claim_by_disk(rdev->bdev, rdev->bdev->bd_holder, mddev->gendisk);
 	return 0;
@@ -1491,7 +1493,8 @@ static void unbind_rdev_from_array(mdk_rdev_t * rdev)
 	printk(KERN_INFO "md: unbind<%s>\n", bdevname(rdev->bdev,b));
 	rdev->mddev = NULL;
 	sysfs_remove_link(&rdev->kobj, "block");
-
+	sysfs_put(rdev->sysfs_state);
+	rdev->sysfs_state = NULL;
 	/* We need to delay this, otherwise we can deadlock when
 	 * writing to 'remove' to "dev/state".  We also need
 	 * to delay it due to rcu usage.
@@ -1926,8 +1929,8 @@ state_store(mdk_rdev_t *rdev, const char *buf, size_t len)
 
 		err = 0;
 	}
-	if (!err)
-		sysfs_notify(&rdev->kobj, NULL, "state");
+	if (!err && rdev->sysfs_state)
+		sysfs_notify_dirent(rdev->sysfs_state);
 	return err ? err : len;
 }
 static struct rdev_sysfs_entry rdev_state =
@@ -2022,7 +2025,7 @@ slot_store(mdk_rdev_t *rdev, const char *buf, size_t len)
 			rdev->raid_disk = -1;
 			return err;
 		} else
-			sysfs_notify(&rdev->kobj, NULL, "state");
+			sysfs_notify_dirent(rdev->sysfs_state);
 		sprintf(nm, "rd%d", rdev->raid_disk);
 		if (sysfs_create_link(&rdev->mddev->kobj, &rdev->kobj, nm))
 			printk(KERN_WARNING
@@ -2039,7 +2042,7 @@ slot_store(mdk_rdev_t *rdev, const char *buf, size_t len)
 		clear_bit(Faulty, &rdev->flags);
 		clear_bit(WriteMostly, &rdev->flags);
 		set_bit(In_sync, &rdev->flags);
-		sysfs_notify(&rdev->kobj, NULL, "state");
+		sysfs_notify_dirent(rdev->sysfs_state);
 	}
 	return len;
 }
@@ -3583,7 +3586,7 @@ static int do_md_run(mddev_t * mddev)
 				return -EINVAL;
 			}
 		}
-		sysfs_notify(&rdev->kobj, NULL, "state");
+		sysfs_notify_dirent(rdev->sysfs_state);
 	}
 
 	md_probe(mddev->unit, NULL, NULL);
@@ -4302,7 +4305,7 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info)
 		if (err)
 			export_rdev(rdev);
 		else
-			sysfs_notify(&rdev->kobj, NULL, "state");
+			sysfs_notify_dirent(rdev->sysfs_state);
 
 		md_update_sb(mddev, 1);
 		if (mddev->degraded)
@@ -6113,7 +6116,7 @@ void md_check_recovery(mddev_t *mddev)
 
 		rdev_for_each(rdev, rtmp, mddev)
 			if (test_and_clear_bit(StateChanged, &rdev->flags))
-				sysfs_notify(&rdev->kobj, NULL, "state");
+				sysfs_notify_dirent(rdev->sysfs_state);
 
 
 		if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) &&
@@ -6223,7 +6226,7 @@ void md_check_recovery(mddev_t *mddev)
 
 void md_wait_for_blocked_rdev(mdk_rdev_t *rdev, mddev_t *mddev)
 {
-	sysfs_notify(&rdev->kobj, NULL, "state");
+	sysfs_notify_dirent(rdev->sysfs_state);
 	wait_event_timeout(rdev->blocked_wait,
 			   !test_bit(Blocked, &rdev->flags),
 			   msecs_to_jiffies(5000));

include/linux/raid/md_k.h

@@ -115,6 +115,9 @@ struct mdk_rdev_s
 					   * in superblock.
 					   */
 	struct work_struct del_work;	/* used for delayed sysfs removal */
+
+	struct sysfs_dirent *sysfs_state; /* handle for 'state'
+					   * sysfs entry */
 };
 
 struct mddev_s