On Fri, Feb 02, 2024 at 03:47:55PM +0100, Hanna Czenczek wrote: > scsi_device_for_each_req_async() currently does not provide any way to > be awaited. One of its callers is scsi_device_purge_requests(), which > therefore currently does not guarantee that all requests are fully > settled when it returns. > > We want all requests to be settled, because scsi_device_purge_requests() > is called through the unrealize path, including the one invoked by > virtio_scsi_hotunplug() through qdev_simple_device_unplug_cb(), which > most likely assumes that all SCSI requests are done then. > > In fact, scsi_device_purge_requests() already contains a blk_drain(), > but this will not fully await scsi_device_for_each_req_async(), only the > I/O requests it potentially cancels (not the non-I/O requests). > However, we can have scsi_device_for_each_req_async() increment the BB > in-flight counter, and have scsi_device_for_each_req_async_bh() > decrement it when it is done. This way, the blk_drain() will fully > await all SCSI requests to be purged. > > This also removes the need for scsi_device_for_each_req_async_bh() to > double-check the current context and potentially re-schedule itself, > should it now differ from the BB's context: Changing a BB's AioContext > with a root node is done through bdrv_try_change_aio_context(), which > creates a drained section. With this patch, we keep the BB in-flight > counter elevated throughout, so we know the BB's context cannot change. > > Signed-off-by: Hanna Czenczek <hre...@redhat.com> > --- > hw/scsi/scsi-bus.c | 30 +++++++++++++++++++++--------- > 1 file changed, 21 insertions(+), 9 deletions(-)
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
signature.asc
Description: PGP signature
