Messages in this thread Patch in this message | | | Date | Mon, 1 Feb 2021 11:21:20 +0100 | From | Stefano Garzarella <> | Subject | Re: [PATCH RFC v2 03/10] vringh: reset kiov 'consumed' field in __vringh_iov() |
| |
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?
Maybe I should add a comment in vringh.c to explain this better.
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; >
| |