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
>
