Messages in this thread | | | Subject | Re: [PATCH RFC v2 03/10] vringh: reset kiov 'consumed' field in __vringh_iov() | From | Jason Wang <> | Date | Tue, 2 Feb 2021 11:26:31 +0800 |
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On 2021/2/1 下午6:21, Stefano Garzarella wrote: > On Mon, Feb 01, 2021 at 01:40:01PM +0800, Jason Wang wrote: >> >> On 2021/1/28 下午10:41, Stefano Garzarella wrote: >>> __vringh_iov() overwrites the contents of riov and wiov, in fact it >>> resets the 'i' and 'used' fields, but also the consumed field should >>> be reset to avoid an inconsistent state. >>> >>> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com> >> >> >> I had a question(I remember we had some discussion like this but I >> forget the conclusion): > > Sorry, I forgot to update you. > >> >> I see e.g in vringh_getdesc_kern() it has the following comment: >> >> /* >> * Note that you may need to clean up riov and wiov, even on error! >> */ >> >> So it looks to me the correct way is to call vringh_kiov_cleanup() >> before? > > Looking at the code the right pattern should be: > > vringh_getdesc_*(..., &out_iov, &in_iov, ...); > > // use out_iov and in_iov > > vringh_kiov_cleanup(&out_iov); > vringh_kiov_cleanup(&in_iov); > > This because vringh_getdesc_*() calls __vringh_iov() where > resize_iovec() is called to allocate the iov wrapped by 'struct > vringh_kiov' and vringh_kiov_cleanup() frees that memory. > > Looking better, __vringh_iov() is able to extend a 'vringh_kiov' > pre-allocated, so in order to avoid to allocate and free the iov for > each request we can avoid to call vringh_kiov_cleanup(), but this > patch is needed to avoid an inconsistent state. > > And also patch "vdpa_sim: cleanup kiovs in vdpasim_free()" is required > to free the iov when the device is going away. > > Does that make sense to you?
Make sense.
> > Maybe I should add a comment in vringh.c to explain this better.
Yes, please.
Thanks
> > Thanks, > Stefano > >> >> Thanks >> >> >>> --- >>> drivers/vhost/vringh.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c >>> index f68122705719..bee63d68201a 100644 >>> --- a/drivers/vhost/vringh.c >>> +++ b/drivers/vhost/vringh.c >>> @@ -290,9 +290,9 @@ __vringh_iov(struct vringh *vrh, u16 i, >>> return -EINVAL; >>> if (riov) >>> - riov->i = riov->used = 0; >>> + riov->i = riov->used = riov->consumed = 0; >>> if (wiov) >>> - wiov->i = wiov->used = 0; >>> + wiov->i = wiov->used = wiov->consumed = 0; >>> for (;;) { >>> void *addr; >> >
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