>
> On Wed, Mar 24, 2021 at 3:46 PM Ciara Loftus <ciara.loftus@xxxxxxxxx>
> wrote:
> >
> > If the call to socket_create fails, the user may want to retry the
> > socket creation using the same umem. Ensure that the umem is in the
> > same state on exit if the call failed by restoring the _save pointers
> > and not unmapping the set of umem rings if those pointers are non NULL.
> >
> > Fixes: 2f6324a3937f ("libbpf: Support shared umems between queues and
> devices")
> >
> > Signed-off-by: Ciara Loftus <ciara.loftus@xxxxxxxxx>
> > ---
> > tools/lib/bpf/xsk.c | 29 ++++++++++++++++++-----------
> > 1 file changed, 18 insertions(+), 11 deletions(-)
> >
> > diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> > index 443b0cfb45e8..ec3c23299329 100644
> > --- a/tools/lib/bpf/xsk.c
> > +++ b/tools/lib/bpf/xsk.c
> > @@ -743,21 +743,23 @@ static struct xsk_ctx *xsk_get_ctx(struct
> xsk_umem *umem, int ifindex,
> > return NULL;
> > }
> >
> > -static void xsk_put_ctx(struct xsk_ctx *ctx)
> > +static void xsk_put_ctx(struct xsk_ctx *ctx, bool unmap)
> > {
> > struct xsk_umem *umem = ctx->umem;
> > struct xdp_mmap_offsets off;
> > int err;
> >
> > if (--ctx->refcount == 0) {
> > - err = xsk_get_mmap_offsets(umem->fd, &off);
> > - if (!err) {
> > - munmap(ctx->fill->ring - off.fr.desc,
> > - off.fr.desc + umem->config.fill_size *
> > - sizeof(__u64));
> > - munmap(ctx->comp->ring - off.cr.desc,
> > - off.cr.desc + umem->config.comp_size *
> > - sizeof(__u64));
> > + if (unmap) {
> > + err = xsk_get_mmap_offsets(umem->fd, &off);
> > + if (!err) {
> > + munmap(ctx->fill->ring - off.fr.desc,
> > + off.fr.desc + umem->config.fill_size *
> > + sizeof(__u64));
> > + munmap(ctx->comp->ring - off.cr.desc,
> > + off.cr.desc + umem->config.comp_size *
> > + sizeof(__u64));
> > + }
> > }
>
> By not unmapping these rings we actually leave more state after a
> failed socket creation. So how about skipping this logic (and
In the case of the _save rings, the maps existed before the call to
xsk_socket__create. They were created during xsk_umem__create.
So we should preserve these maps in event of failure.
I was using the wrong condition to trigger the unmap in v1 however.
We should unmap 'fill' only if
umem->fill_save != fill
I will update this in a v2.
> everything below) and always unmap the rings at failure as before, but
> we move the fill_save = NULL and comp_save = NULL from xsk_create_ctx
> to the end of xsk_socket__create_shared just before the "return 0"
> where we know that the whole operation has succeeded. This way the
I think moving these still makes sense and will add this in the next rev.
Thanks for the feedback and suggestions!
Ciara
> mappings would be redone during the next xsk_socket__create and if
> someone decides not to retry (for some reason) we do not leave two
> mappings behind. Would simplify things. What do you think?
>
> >
> > list_del(&ctx->list);
> > @@ -854,6 +856,9 @@ int xsk_socket__create_shared(struct xsk_socket
> **xsk_ptr,
> > struct xsk_socket *xsk;
> > struct xsk_ctx *ctx;
> > int err, ifindex;
> > + struct xsk_ring_prod *fsave = umem->fill_save;
> > + struct xsk_ring_cons *csave = umem->comp_save;
> > + bool unmap = !fsave;
> >
> > if (!umem || !xsk_ptr || !(rx || tx))
> > return -EFAULT;
> > @@ -1005,7 +1010,9 @@ int xsk_socket__create_shared(struct xsk_socket
> **xsk_ptr,
> > munmap(rx_map, off.rx.desc +
> > xsk->config.rx_size * sizeof(struct xdp_desc));
> > out_put_ctx:
> > - xsk_put_ctx(ctx);
> > + umem->fill_save = fsave;
> > + umem->comp_save = csave;
> > + xsk_put_ctx(ctx, unmap);
> > out_socket:
> > if (--umem->refcount)
> > close(xsk->fd);
> > @@ -1071,7 +1078,7 @@ void xsk_socket__delete(struct xsk_socket *xsk)
> > }
> > }
> >
> > - xsk_put_ctx(ctx);
> > + xsk_put_ctx(ctx, true);
> >
> > umem->refcount--;
> > /* Do not close an fd that also has an associated umem connected
> > --
> > 2.17.1
> >
