Re: [PATCH 3/5] blktrace: refcount the request_queue during ioctl

[Christoph Hellwig]

On Wed, Apr 15, 2020 at 06:16:49AM +0000, Luis Chamberlain wrote:
> The BLKTRACESETUP above works on request_queue which later
> LOOP_CTL_DEL races on and sweeps the debugfs dir underneath us.
> If you use this commit alone though, this doesn't fix the race issue
> however, and that's because of both still the debugfs_lookup() use
> and that we're still using asynchronous removal at this point.
> 
> refcounting will just ensure we don't take the request_queue underneath
> our noses.
> 
> Should I just add this to the commit log?

That sounds much more useful than the trace.

Btw, Isn't blk_get_queue racy as well?  Shouldn't we check
blk_queue_dying after getting the reference and undo it if the queue is
indeeed dying?