Re: [PATCH 1/4] scsi: only access SCSIDevice->requests from one thread

[Eric Blake]

On Thu, Nov 23, 2023 at 02:49:28PM -0500, Stefan Hajnoczi wrote:
> Stop depending on the AioContext lock and instead access
> SCSIDevice->requests from only one thread at a time:
> - When the VM is running only the BlockBackend's AioContext may access
>   the requests list.
> - When the VM is stopped only the main loop may access the requests
>   list.
> 
> These constraints protect the requests list without the need for locking
> in the I/O code path.
> 
> Note that multiple IOThreads are not supported yet because the code
> assumes all SCSIRequests are executed from a single AioContext. Leave
> that as future work.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  include/hw/scsi/scsi.h |   7 +-
>  hw/scsi/scsi-bus.c     | 174 ++++++++++++++++++++++++++++-------------
>  2 files changed, 124 insertions(+), 57 deletions(-)
>

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org