Re: [PATCH v2] scsi: sr: get rid of sr global mutex

[Christoph Hellwig]

On Tue, Feb 18, 2020 at 03:39:17PM +0100, Merlijn Wajer wrote:
> When replacing the Big Kernel Lock in commit
> 2a48fc0ab24241755dc93bfd4f01d68efab47f5a ("block: autoconvert trivial
> BKL users to private mutex"), the lock was replaced with a sr-wide lock.
> 
> This causes very poor performance when using multiple sr devices, as the
> sr driver was not able to execute more than one command to one drive at
> any given time, even when there were many CD drives available.
> 
> Replace the global mutex with per-sr-device mutex.

Do we actually need the lock at all?  What is protected by it?