Re: [PATCH V2 2/2] block: fix "Directory XXXXX with parent 'block' already present!"

[Ming Lei <ming.lei@redhat.com>]

On Sat, Apr 23, 2022 at 06:29:37PM +0200, Christoph Hellwig wrote:
> On Sat, Apr 23, 2022 at 10:39:52PM +0800, Ming Lei wrote:
> > q->debugfs_dir is used by blk-mq debugfs and blktrace. The dentry is
> > created when adding disk, and removed when releasing request queue.
> > 
> > There is small window between releasing disk and releasing request
> > queue, and during the period, one disk with same name may be created
> > and added, so debugfs_create_dir() may complain with "Directory XXXXX
> > with parent 'block' already present!"
> > 
> > Fixes the issue by moving debugfs_create_dir() into blk_alloc_queue(),
> > and the dir name is named with q->id from beginning, and switched to
> > disk name when adding disk, and finally changed to q->id in disk_release().
> 
> As said before I very much think this is going in the wrong direction.

So far I'd suggest to keep q->debugfs_dir inside request queue, another
goodness is that we can use it for exposing non-blk qeueue's debug info,
and there is request queue without gendisk attached.

> 
> As the debugfs directory use the name of the gendisk, the lifetime rules
> should simply match those of the gendisk.  If anyone wants to trace
> SCSI commands sent before probing the gendisk or after removing it
> they can use blktrace on the /dev/sg node.

Not sure blktrace can trace on /dev/sg since blktrace works on
block_device.


Thanks, 
Ming