Re: [PATCH 1/2] io_uring: add uring_lock as an argument to io_sqe_files_unregister()

Pavel Begunkov
2021-02-03T16:38:34Z

On 03/02/2021 14:57, Hao Xu wrote:
> io_sqe_files_unregister is currently called from several places:
> - syscall io_uring_register (with uring_lock)
> - io_ring_ctx_wait_and_kill() (without uring_lock)
>
> There is a AA type deadlock in io_sqe_files_unregister(), thus we need
> to know if we hold uring_lock in io_sqe_files_unregister() to fix the
> issue.

It's ugly, just take the lock and kill the patch. There can't be any
contention during io_ring_ctx_free anyway.

>
> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
> ---
> fs/io_uring.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 38c6cbe1ab38..efb6d02fea6f 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -7339,7 +7339,7 @@ static void io_sqe_files_set_node(struct fixed_file_data *file_data,
> percpu_ref_get(&file_data->refs);
> }
>
> -static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
> +static int io_sqe_files_unregister(struct io_ring_ctx *ctx, bool locked)
> {
> struct fixed_file_data *data = ctx->file_data;
> struct fixed_file_ref_node *backup_node, *ref_node = NULL;
> @@ -7872,13 +7872,13 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
>
> ret = io_sqe_files_scm(ctx);
> if (ret) {
> - io_sqe_files_unregister(ctx);
> + io_sqe_files_unregister(ctx, true);
> return ret;
> }
>
> ref_node = alloc_fixed_file_ref_node(ctx);
> if (!ref_node) {
> - io_sqe_files_unregister(ctx);
> + io_sqe_files_unregister(ctx, true);
> return -ENOMEM;
> }
>
> @@ -8682,7 +8682,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
> css_put(ctx->sqo_blkcg_css);
> #endif
>
> - io_sqe_files_unregister(ctx);
> + io_sqe_files_unregister(ctx, false);
> io_eventfd_unregister(ctx);
> io_destroy_buffers(ctx);
> idr_destroy(&ctx->personality_idr);
> @@ -10065,7 +10065,7 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
> ret = -EINVAL;
> if (arg || nr_args)
> break;
> - ret = io_sqe_files_unregister(ctx);
> + ret = io_sqe_files_unregister(ctx, true);
> break;
> case IORING_REGISTER_FILES_UPDATE:
> ret = io_sqe_files_update(ctx, arg, nr_args);
>

--
Pavel Begunkov