From: Christoph Hellwig hch@lst.de
[ Upstream commit 7df835a32a8bedf7ce88efcfa7c9b245b52ff139 ]
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@syzkaller.appspotmail.com Signed-off-by: Christoph Hellwig hch@lst.de Tested-by: syzbot+fadc0aaf497e6a493b9f@syzkaller.appspotmail.com Reviewed-by: NeilBrown neilb@suse.de Signed-off-by: Song Liu songliubraving@fb.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/md/md.c | 5 ----- 1 file changed, 5 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c index 761d43829b2b..c178b2f406de 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -5535,10 +5535,6 @@ static int md_alloc(dev_t dev, char *name) */ disk->flags |= GENHD_FL_EXT_DEVT; 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"); @@ -5553,7 +5549,6 @@ 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) {