From: Akinobu Mita blk_register_queue() returns -ENXIO when queue->request_fn is NULL. But there are some block drivers that call blk_register_queue() via add_disk() with queue->request_fn == NULL. (For example, brd, loop) Although no one checks return value of blk_register_queue(), this patch makes it return 0 instead of -ENXIO when queue->request_fn is NULL, Also this patch adds warning when blk_register_queue() and blk_unregister_queue() are called with queue == NULL rather than ignore invalid usage silently. Signed-off-by: Akinobu Mita Cc: Jens Axboe Signed-off-by: Andrew Morton --- block/blk-sysfs.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff -puN block/blk-sysfs.c~block-fix-blk_register_queue-return-value block/blk-sysfs.c --- a/block/blk-sysfs.c~block-fix-blk_register_queue-return-value +++ a/block/blk-sysfs.c @@ -276,9 +276,12 @@ int blk_register_queue(struct gendisk *d struct request_queue *q = disk->queue; - if (!q || !q->request_fn) + if (WARN_ON(!q)) return -ENXIO; + if (!q->request_fn) + return 0; + ret = kobject_add(&q->kobj, kobject_get(&disk->dev.kobj), "%s", "queue"); if (ret < 0) @@ -300,7 +303,10 @@ void blk_unregister_queue(struct gendisk { struct request_queue *q = disk->queue; - if (q && q->request_fn) { + if (WARN_ON(!q)) + return; + + if (q->request_fn) { elv_unregister_queue(q); kobject_uevent(&q->kobj, KOBJ_REMOVE); _