forked from Minki/linux
md: fix a lock order reversal in md_alloc
Commitb0140891a8
("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:b0140891a8
("md: Fix race when creating a new md device.") Fixes:d626338735
("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>
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@ -5700,10 +5700,6 @@ static int md_alloc(dev_t dev, char *name)
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disk->flags |= GENHD_FL_EXT_DEVT;
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disk->events |= DISK_EVENT_MEDIA_CHANGE;
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mddev->gendisk = disk;
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/* As soon as we call add_disk(), another thread could get
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* through to md_open, so make sure it doesn't get too far
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*/
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mutex_lock(&mddev->open_mutex);
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add_disk(disk);
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error = kobject_add(&mddev->kobj, &disk_to_dev(disk)->kobj, "%s", "md");
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@ -5718,7 +5714,6 @@ static int md_alloc(dev_t dev, char *name)
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if (mddev->kobj.sd &&
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sysfs_create_group(&mddev->kobj, &md_bitmap_group))
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pr_debug("pointless warning\n");
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mutex_unlock(&mddev->open_mutex);
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abort:
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mutex_unlock(&disks_mutex);
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if (!error && mddev->kobj.sd) {
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