Re: [PATCH 2/2] io_uring: unlock if __io_run_local_work locked inside

[Jens Axboe <axboe@kernel.dk>]

On 10/27/22 8:44 AM, Dylan Yudaken wrote:
> It is possible for tw to lock the ring, and this was not propogated out to
> io_run_local_work. This can cause an unlock to be missed.
> 
> Instead pass a pointer to locked into __io_run_local_work.
> 
> Fixes: 8ac5d85a89b4 ("io_uring: add local task_work run helper that is entered locked")
> Signed-off-by: Dylan Yudaken <dylany@meta.com>
> ---
>  io_uring/io_uring.c |  8 ++++----
>  io_uring/io_uring.h | 12 ++++++++++--
>  2 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 8a0ce7379e89..ac8c488e3077 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -1173,7 +1173,7 @@ static void __cold io_move_task_work_from_local(struct io_ring_ctx *ctx)
>  	}
>  }
>  
> -int __io_run_local_work(struct io_ring_ctx *ctx, bool locked)
> +int __io_run_local_work(struct io_ring_ctx *ctx, bool *locked)
>  {
>  	struct llist_node *node;
>  	struct llist_node fake;
> @@ -1192,7 +1192,7 @@ int __io_run_local_work(struct io_ring_ctx *ctx, bool locked)
>  		struct io_kiocb *req = container_of(node, struct io_kiocb,
>  						    io_task_work.node);
>  		prefetch(container_of(next, struct io_kiocb, io_task_work.node));
> -		req->io_task_work.func(req, &locked);
> +		req->io_task_work.func(req, locked);
>  		ret++;
>  		node = next;
>  	}
> @@ -1208,7 +1208,7 @@ int __io_run_local_work(struct io_ring_ctx *ctx, bool locked)
>  		goto again;
>  	}
>  
> -	if (locked)
> +	if (*locked)
>  		io_submit_flush_completions(ctx);
>  	trace_io_uring_local_work_run(ctx, ret, loops);
>  	return ret;
> @@ -1225,7 +1225,7 @@ int io_run_local_work(struct io_ring_ctx *ctx)
>  
>  	__set_current_state(TASK_RUNNING);
>  	locked = mutex_trylock(&ctx->uring_lock);
> -	ret = __io_run_local_work(ctx, locked);
> +	ret = __io_run_local_work(ctx, &locked);
>  	if (locked)
>  		mutex_unlock(&ctx->uring_lock);
>  
> diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
> index ef77d2aa3172..331ec2869212 100644
> --- a/io_uring/io_uring.h
> +++ b/io_uring/io_uring.h
> @@ -27,7 +27,7 @@ enum {
>  struct io_uring_cqe *__io_get_cqe(struct io_ring_ctx *ctx, bool overflow);
>  bool io_req_cqe_overflow(struct io_kiocb *req);
>  int io_run_task_work_sig(struct io_ring_ctx *ctx);
> -int __io_run_local_work(struct io_ring_ctx *ctx, bool locked);
> +int __io_run_local_work(struct io_ring_ctx *ctx, bool *locked);
>  int io_run_local_work(struct io_ring_ctx *ctx);
>  void io_req_complete_failed(struct io_kiocb *req, s32 res);
>  void __io_req_complete(struct io_kiocb *req, unsigned issue_flags);
> @@ -277,9 +277,17 @@ static inline int io_run_task_work_ctx(struct io_ring_ctx *ctx)
>  
>  static inline int io_run_local_work_locked(struct io_ring_ctx *ctx)
>  {
> +	bool locked;
> +	int ret;
> +
>  	if (llist_empty(&ctx->work_llist))
>  		return 0;
> -	return __io_run_local_work(ctx, true);
> +
> +	locked = true;
> +	ret = __io_run_local_work(ctx, &locked);
> +	if (WARN_ON(!locked))
> +		mutex_lock(&ctx->uring_lock);
> +	return ret;
>  }

If you think warning on !locked is a good idea, it should be a
WARN_ON_ONCE(). Or is this leftover debugging?

-- 
Jens Axboe