Commit b0140891a8cea3 ("md: Fix race when creating a new md device.")
not only moved assigning mddev->gendisk before calling add_disk, which
fixes the races described in the commit log, but also added a
mddev->open_mutex critical section over add_disk and creation of the
md kobj. Adding a kobject after add_disk is racy vs deleting the gendisk
right after adding it, but md already prevents against that by holding
a mddev->active reference.
On the other hand taking this lock added a lock order reversal with what
is not disk->open_mutex (used to be bdev->bd_mutex when the commit was
added) for partition devices, which need that lock for the internal open
for the partition scan, and a recent commit also takes it for
non-partitioned devices, leading to further lockdep splatter.
Fixes: b0140891a8ce ("md: Fix race when creating a new md device.")
Fixes: d62633873590 ("block: support delayed holder registration")
Reported-by: syzbot+fadc0aaf497e6a493b9f@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Tested-by: syzbot+fadc0aaf497e6a493b9f@xxxxxxxxxxxxxxxxxxxxxxxxx
---
drivers/md/md.c | 5 -----
1 file changed, 5 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index ae8fe54ea3581..6c0c3d0d905aa 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5700,10 +5700,6 @@ static int md_alloc(dev_t dev, char *name)
disk->flags |= GENHD_FL_EXT_DEVT;
disk->events |= DISK_EVENT_MEDIA_CHANGE;
mddev->gendisk = disk;
- /* As soon as we call add_disk(), another thread could get
- * through to md_open, so make sure it doesn't get too far
- */
- mutex_lock(&mddev->open_mutex);
add_disk(disk);
error = kobject_add(&mddev->kobj, &disk_to_dev(disk)->kobj, "%s", "md");
@@ -5718,7 +5714,6 @@ static int md_alloc(dev_t dev, char *name)
if (mddev->kobj.sd &&
sysfs_create_group(&mddev->kobj, &md_bitmap_group))
pr_debug("pointless warning\n");
- mutex_unlock(&mddev->open_mutex);
abort:
mutex_unlock(&disks_mutex);
if (!error && mddev->kobj.sd) {
--
2.30.2
