Re: [PATCH v2 1/6] io_uring/zcrx: add ctx pointer to zcrx

On Mon, May 18, 2026 at 8:36 AM Clément Léger <[email protected]> wrote:
>
> From: Pavel Begunkov <[email protected]>
>
> zcrx will need to have a pointer to an owning ctx to communicate
> different events. Reference the ctx while it's attached to zcrx, and
> rely on zcrx termination to drop the ctx to avoid circular ref deps.
>
> Co-developed-by: Vishwanath Seshagiri <[email protected]>
> Signed-off-by: Pavel Begunkov <[email protected]>
Signed-off-by: Vishwanath Seshagiri <[email protected]>
> ---
>  io_uring/zcrx.c | 39 +++++++++++++++++++++++++++++++--------
>  io_uring/zcrx.h |  3 +++
>  2 files changed, 34 insertions(+), 8 deletions(-)
>
> diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
> index 3f9632e7790a..34faf90423f4 100644
> --- a/io_uring/zcrx.c
> +++ b/io_uring/zcrx.c
> @@ -44,6 +44,17 @@ static inline struct io_zcrx_area *io_zcrx_iov_to_area(const struct net_iov *nio
>         return container_of(owner, struct io_zcrx_area, nia);
>  }
>
> +static bool zcrx_set_ring_ctx(struct io_zcrx_ifq *zcrx,
> +                             struct io_ring_ctx *ctx)
> +{
> +       guard(spinlock_bh)(&zcrx->ctx_lock);
> +       if (zcrx->master_ctx)
> +               return false;
> +       percpu_ref_get(&ctx->refs);
> +       zcrx->master_ctx = ctx;
> +       return true;
> +}
> +
>  static inline struct page *io_zcrx_iov_page(const struct net_iov *niov)
>  {
>         struct io_zcrx_area *area = io_zcrx_iov_to_area(niov);
> @@ -531,6 +542,7 @@ static struct io_zcrx_ifq *io_zcrx_ifq_alloc(struct io_ring_ctx *ctx)
>                 return NULL;
>
>         ifq->if_rxq = -1;
> +       spin_lock_init(&ifq->ctx_lock);
>         spin_lock_init(&ifq->rq.lock);
>         mutex_init(&ifq->pp_lock);
>         refcount_set(&ifq->refs, 1);
> @@ -580,6 +592,8 @@ static void io_zcrx_ifq_free(struct io_zcrx_ifq *ifq)
>                 return;
>         if (WARN_ON_ONCE(ifq->netdev != NULL))
>                 return;
> +       if (WARN_ON_ONCE(ifq->master_ctx))
> +               return;
>
>         if (ifq->area)
>                 io_zcrx_free_area(ifq, ifq->area);
> @@ -656,17 +670,24 @@ static void io_zcrx_scrub(struct io_zcrx_ifq *ifq)
>         }
>  }
>
> -static void zcrx_unregister_user(struct io_zcrx_ifq *ifq)
> +static void zcrx_unregister_user(struct io_zcrx_ifq *ifq, struct io_ring_ctx *ctx)
>  {
> +       scoped_guard(spinlock_bh, &ifq->ctx_lock) {
> +               if (ctx && ifq->master_ctx == ctx) {
> +                       ifq->master_ctx = NULL;
> +                       percpu_ref_put(&ctx->refs);
> +               }
> +       }
> +
>         if (refcount_dec_and_test(&ifq->user_refs)) {
>                 io_close_queue(ifq);
>                 io_zcrx_scrub(ifq);
>         }
>  }
>
> -static void zcrx_unregister(struct io_zcrx_ifq *ifq)
> +static void zcrx_unregister(struct io_zcrx_ifq *ifq, struct io_ring_ctx *ctx)
>  {
> -       zcrx_unregister_user(ifq);
> +       zcrx_unregister_user(ifq, ctx);
>         io_put_zcrx_ifq(ifq);
>  }
>
> @@ -686,7 +707,7 @@ static int zcrx_box_release(struct inode *inode, struct file *file)
>
>         if (WARN_ON_ONCE(!ifq))
>                 return -EFAULT;
> -       zcrx_unregister(ifq);
> +       zcrx_unregister(ifq, NULL);
>         return 0;
>  }
>
> @@ -711,7 +732,7 @@ static int zcrx_export(struct io_ring_ctx *ctx, struct io_zcrx_ifq *ifq,
>         file = anon_inode_create_getfile("[zcrx]", &zcrx_box_fops,
>                                          ifq, O_CLOEXEC, NULL);
>         if (IS_ERR(file)) {
> -               zcrx_unregister(ifq);
> +               zcrx_unregister(ifq, NULL);
>                 return PTR_ERR(file);
>         }
>
> @@ -787,7 +808,7 @@ static int import_zcrx(struct io_ring_ctx *ctx,
>         scoped_guard(mutex, &ctx->mmap_lock)
>                 xa_erase(&ctx->zcrx_ctxs, id);
>  err:
> -       zcrx_unregister(ifq);
> +       zcrx_unregister(ifq, ctx);
>         return ret;
>  }
>
> @@ -932,12 +953,14 @@ int io_register_zcrx(struct io_ring_ctx *ctx,
>                 ret = -EFAULT;
>                 goto err;
>         }
> +
> +       zcrx_set_ring_ctx(ifq, ctx);
>         return 0;
>  err:
>         scoped_guard(mutex, &ctx->mmap_lock)
>                 xa_erase(&ctx->zcrx_ctxs, id);
>  ifq_free:
> -       zcrx_unregister(ifq);
> +       zcrx_unregister(ifq, ctx);
>         return ret;
>  }
>
> @@ -967,7 +990,7 @@ void io_terminate_zcrx(struct io_ring_ctx *ctx)
>                         break;
>                 set_zcrx_entry_mark(ctx, id);
>                 id++;
> -               zcrx_unregister_user(ifq);
> +               zcrx_unregister_user(ifq, ctx);
>         }
>  }
>
> diff --git a/io_uring/zcrx.h b/io_uring/zcrx.h
> index 9e1a6a1b11e8..6b565d0bf6da 100644
> --- a/io_uring/zcrx.h
> +++ b/io_uring/zcrx.h
> @@ -73,6 +73,9 @@ struct io_zcrx_ifq {
>          */
>         struct mutex                    pp_lock;
>         struct io_mapped_region         rq_region;
> +
> +       spinlock_t                      ctx_lock;
> +       struct io_ring_ctx              *master_ctx;
>  };
>
>  #if defined(CONFIG_IO_URING_ZCRX)
> --
> 2.53.0-Meta
>