On Thu, Apr 12, 2018 at 04:29:09PM +0000, Bart Van Assche wrote:
> Any code that submits a bio or request needs blk_queue_enter() /
> blk_queue_exit() anyway. Please have a look at the following commit - you will
> see that that commit reduces the number of blk_queue_enter() / 
> blk_queue_exit()
> calls in the hot path:
> https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=for-linus&id=37f9579f4c31a6d698dbf3016d7bf132f9288d30

So, this can work, but it's still pretty fragile.

* Lock switching is fragile and we really should get rid of it.  This
  is very likely to come back and bite us.

* Right now, blk_queue_enter/exit() doesn't have any annotations.
  IOW, there's no way for paths which need enter locked to actually
  assert that.  If we're gonna protect more things with queue
  enter/exit, it gotta be annotated.



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