Re: [PATCH v4] io_uring: annotate remote tasks for kcoverage

On Wed, Jun 24, 2026 at 11:03 AM Robert Femmer <[email protected]> wrote:
>
> Fuzzers use coverage information to guide generation of test cases
> towards new or interesting code paths. Syzkaller, specifically, makes
> use kcoverage (CONFIG_KCOV). Coverage information is not collected for
> kernel tasks unless annotated by kcov_remote_start and kcov_remote_stop.
> This patch annotates io-uring's work queue and sqpoll tasks.
>
> Depends-On: 20260430-kcov-refactor-common-handle-v1-1-23a0c7a0ba38@google.com
> Signed-off-by: Robert Femmer <[email protected]>
> ---
>  include/linux/io_uring_types.h | 2 ++
>  io_uring/io-wq.c               | 5 +++++
>  io_uring/io_uring.c            | 2 ++
>  io_uring/sqpoll.c              | 3 +++
>  4 files changed, 12 insertions(+)
>
> diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
> index 244392026c6d..b6590b2b350c 100644
> --- a/include/linux/io_uring_types.h
> +++ b/include/linux/io_uring_types.h
> @@ -504,6 +504,8 @@ struct io_ring_ctx {
>         struct io_mapped_region         ring_region;
>         /* used for optimised request parameter and wait argument passing  */
>         struct io_mapped_region         param_region;
> +
> +       struct kcov_common_handle_id    kcov_handle;
>  };
>
>  /*
> diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c
> index 8cc7b47d3089..173299dfc9c2 100644
> --- a/io_uring/io-wq.c
> +++ b/io_uring/io-wq.c
> @@ -19,6 +19,7 @@
>  #include <linux/mmu_context.h>
>  #include <linux/sched/sysctl.h>
>  #include <uapi/linux/io_uring.h>
> +#include <linux/kcov.h>
>
>  #include "io-wq.h"
>  #include "slist.h"
> @@ -639,6 +640,7 @@ static void io_worker_handle_work(struct io_wq_acct *acct,
>                 /* handle a whole dependent link */
>                 do {
>                         struct io_wq_work *next_hashed, *linked;
> +                       struct io_kiocb *req;
>                         unsigned int work_flags = atomic_read(&work->flags);
>                         unsigned int hash = __io_wq_is_hashed(work_flags)
>                                 ? __io_get_work_hash(work_flags)
> @@ -649,7 +651,10 @@ static void io_worker_handle_work(struct io_wq_acct *acct,
>                         if (do_kill &&
>                             (work_flags & IO_WQ_WORK_UNBOUND))
>                                 atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
> +                       req = container_of(work, struct io_kiocb, work);
> +                       kcov_remote_start_common(req->ctx->kcov_handle);
>                         io_wq_submit_work(work);
> +                       kcov_remote_stop();
>                         io_assign_current_work(worker, NULL);
>
>                         linked = io_wq_free_work(work);
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 103b6c88f252..ab7c3e45e238 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -59,6 +59,7 @@
>  #include <linux/audit.h>
>  #include <linux/security.h>
>  #include <linux/jump_label.h>
> +#include <linux/kcov.h>
>
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/io_uring.h>
> @@ -293,6 +294,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
>         INIT_HLIST_HEAD(&ctx->cancelable_uring_cmd);
>         io_napi_init(ctx);
>         mutex_init(&ctx->mmap_lock);
> +       ctx->kcov_handle = kcov_common_handle();
>
>         return ctx;
>
> diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
> index 46c12afec73e..aafb640d3b2f 100644
> --- a/io_uring/sqpoll.c
> +++ b/io_uring/sqpoll.c
> @@ -13,6 +13,7 @@
>  #include <linux/cpuset.h>
>  #include <linux/sched/cputime.h>
>  #include <linux/io_uring.h>
> +#include <linux/kcov.h>
>
>  #include <uapi/linux/io_uring.h>
>
> @@ -342,10 +343,12 @@ static int io_sq_thread(void *data)
>
>                 cap_entries = !list_is_singular(&sqd->ctx_list);
>                 list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
> +                       kcov_remote_start_common(ctx->kcov_handle);
>                         int ret = __io_sq_thread(ctx, sqd, cap_entries, &ist);
>
>                         if (!sqt_spin && (ret > 0 || !list_empty(&ctx->iopoll_list)))
>                                 sqt_spin = true;
> +                       kcov_remote_stop();
>                 }
>                 if (io_sq_tw(&retry_list, IORING_TW_CAP_ENTRIES_VALUE))
>                         sqt_spin = true;
> --
> 2.54.0
>

From KCOV API side:

Acked-by: Andrey Konovalov <[email protected]>

Thanks!