On Thu, 2018-04-12 at 07:34 +0200, Christoph Hellwig wrote: > On Wed, Apr 11, 2018 at 07:58:52PM -0600, Bart Van Assche wrote: > > Several block drivers call alloc_disk() followed by put_disk() if > > something fails before device_add_disk() is called without calling > > blk_cleanup_queue(). Make sure that also for this scenario a request > > queue is dissociated from the cgroup controller. This patch avoids > > that loading the parport_pc, paride and pf drivers triggers the > > following kernel crash: > > Can we move the cleanup to put_disk in general and not just for > this case? Having alloc/free routines pair up generally avoids > a lot of confusion.
Hello Christoph, At least the SCSI ULP drivers drop the last reference to a disk after the blk_cleanup_queue() call. As explained in the description of commit a063057d7c73, removing a request queue from blkcg must happen before blk_cleanup_queue() finishes because a block driver may free the request queue spinlock immediately after blk_cleanup_queue() returns. So I don't think that we can move the code that removes a request queue from blkcg into put_disk(). Another challenge is that some block drivers (e.g. skd) clear the disk->queue pointer if device_add_disk() has not been called to avoid that put_disk() causes a request queue reference count imbalance. Bart.
