Fix race of "mdadm --add" and "mdadm --incremental"

There is a raid1 with sda and sdb. And we add sdc to this raid,
it may return -EBUSY.

The main process of --add:
1. dev_open（sdc) in Manage_add
2. store_super1(st, di->fd) in write_init_super1
3. fsync(fd) in store_super1
4. close(di->fd) in write_init_super1
5. ioctl(ADD_NEW_DISK)

Step 2 and 3 will add sdc to metadata of raid1. There will be
udev(change of sdc) event after step4. Then "/usr/sbin/mdadm
--incremental --export $devnode --offroot $env{DEVLINKS}"
will be run, and the sdc will be added to the raid1. Then
step 5 will return -EBUSY because it checks if device isn't
claimed in md_import_device()->lock_rdev()->blkdev_get_by_dev()
->blkdev_get().

It will be confusing for users because sdc is added first time.
The "incremental" will get map_lock before add sdc to raid1.
So we add map_lock before write_init_super in "mdadm --add"
to fix the race of "add" and "incremental".

Signed-off-by: Li Xiao Keng <lixiaokeng@huawei.com>
Signed-off-by: Guanqin Miao <miaoguanqin@huawei.com>
Reviewed-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
Signed-off-by: Jes Sorensen <jes@trained-monkey.org>

1 files changed, 16 insertions, 8 deletions

diff --git a/Manage.c b/Manage.c
index f997b163..075dd720 100644
--- a/Manage.c
+++ b/Manage.c
@@ -704,6 +704,7 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 	struct supertype *dev_st;
 	int j;
 	mdu_disk_info_t disc;
+	struct map_ent *map = NULL;
 
 	if (!get_dev_size(tfd, dv->devname, &ldsize)) {
 		if (dv->disposition == 'M')
@@ -907,6 +908,9 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 		disc.raid_disk = 0;
 	}
 
+	if (map_lock(&map))
+		pr_err("failed to get exclusive lock on mapfile when add disk\n");
+
 	if (array->not_persistent==0) {
 		int dfd;
 		if (dv->disposition == 'j')
@@ -918,9 +922,9 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 		dfd = dev_open(dv->devname, O_RDWR | O_EXCL|O_DIRECT);
 		if (tst->ss->add_to_super(tst, &disc, dfd,
 					  dv->devname, INVALID_SECTORS))
-			return -1;
+			goto unlock;
 		if (tst->ss->write_init_super(tst))
-			return -1;
+			goto unlock;
 	} else if (dv->disposition == 'A') {
 		/*  this had better be raid1.
 		 * As we are "--re-add"ing we must find a spare slot
@@ -978,14 +982,14 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 			pr_err("add failed for %s: could not get exclusive access to container\n",
 			       dv->devname);
 			tst->ss->free_super(tst);
-			return -1;
+			goto unlock;
 		}
 
 		/* Check if metadata handler is able to accept the drive */
 		if (!tst->ss->validate_geometry(tst, LEVEL_CONTAINER, 0, 1, NULL,
 		    0, 0, dv->devname, NULL, 0, 1)) {
 			close(container_fd);
-			return -1;
+			goto unlock;
 		}
 
 		Kill(dv->devname, NULL, 0, -1, 0);
@@ -994,7 +998,7 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 					  dv->devname, INVALID_SECTORS)) {
 			close(dfd);
 			close(container_fd);
-			return -1;
+			goto unlock;
 		}
 		if (!mdmon_running(tst->container_devnm))
 			tst->ss->sync_metadata(tst);
@@ -1005,7 +1009,7 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 			       dv->devname);
 			close(container_fd);
 			tst->ss->free_super(tst);
-			return -1;
+			goto unlock;
 		}
 		sra->array.level = LEVEL_CONTAINER;
 		/* Need to set data_offset and component_size */
@@ -1020,7 +1024,7 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 			pr_err("add new device to external metadata failed for %s\n", dv->devname);
 			close(container_fd);
 			sysfs_free(sra);
-			return -1;
+			goto unlock;
 		}
 		ping_monitor(devnm);
 		sysfs_free(sra);
@@ -1034,7 +1038,7 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 			else
 				pr_err("add new device failed for %s as %d: %s\n",
 				       dv->devname, j, strerror(errno));
-			return -1;
+			goto unlock;
 		}
 		if (dv->disposition == 'j') {
 			pr_err("Journal added successfully, making %s read-write\n", devname);
@@ -1045,7 +1049,11 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 	}
 	if (verbose >= 0)
 		pr_err("added %s\n", dv->devname);
+	map_unlock(&map);
 	return 1;
+unlock:
+	map_unlock(&map);
+	return -1;
 }
 
 int Manage_remove(struct supertype *tst, int fd, struct mddev_dev *dv,