Re: [PATCH v3 0/3] virtio-scsi: fix SCSIDevice hot unplug with IOThread

[Kevin Wolf]

Am 21.02.2023 um 22:22 hat Stefan Hajnoczi geschrieben:
> v3:
> - Fix s/see/sees/ typo in Patch 2 commit description [Eric]
> - Add call stack to Patch 3 commit description to make it clear how 
> blk_drain()
>   is invoked [Kevin]
> 
> Unplugging SCSIDevices when virtio-scsi is using an IOThread suffers from race
> conditions:
> - scsi_device_purge_requests() is called from the IOThread in TMF emulation.
>   This is unsafe, it should only be called from the BQL.
> - SCSIRequest->aiocb is not protected by a lock, so there are races between 
> the
>   main loop thread and the IOThread when scsi_device_purge_requests() runs in
>   the main loop thread.
> - DMAAIOCB->acb is not protected by a lock, so there are races in the DMA
>   helpers code when cancelling a request from the main loop thread.
> 
> These fixes solve assertion failures during SCSIDevice hot unplug in
> virtio-scsi with IOThread. Expanding the use of the AioContext lock isn't 
> great
> since we're in the midst of trying to remove it. However, I think this 
> solution
> is appropriate so that stable trees or distros can backport the fix without
> depending on QEMU multi-queue block layer refactoring.
> 
> Special thanks to Qing Wang, who helped me iterate these patches because I
> couldn't reproduce the assertion failures myself.

Thanks, applied to the block branch.

Kevin