Re: [PATCH 2/2] io_uring: don't hold uring_lock when calling io_run_task_work*

Pavel Begunkov
2021-02-03T16:40:35Z

On 03/02/2021 14:57, Hao Xu wrote:
> This is caused by calling io_run_task_work_sig() to do work under
> uring_lock while the caller io_sqe_files_unregister() already held
> uring_lock.
> we need to check if uring_lock is held by us when doing unlock around
> io_run_task_work_sig() since there are code paths down to that place
> without uring_lock held.

1. we don't want to allow parallel io_sqe_files_unregister()s
happening, it's synchronised by uring_lock atm. Otherwise it's
buggy.

2. probably same with unregister and submit.

>
> Reported-by: Abaci <abaci@linux.alibaba.com>
> Fixes: 1ffc54220c44 ("io_uring: fix io_sqe_files_unregister() hangs")
> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
> ---
> fs/io_uring.c | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index efb6d02fea6f..b093977713ee 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -7362,18 +7362,25 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx, bool locked)
>
> /* wait for all refs nodes to complete */
> flush_delayed_work(&ctx->file_put_work);
> + if (locked)
> + mutex_unlock(&ctx->uring_lock);
> do {
> ret = wait_for_completion_interruptible(&data->done);
> if (!ret)
> break;
> ret = io_run_task_work_sig();
> - if (ret < 0) {
> - percpu_ref_resurrect(&data->refs);
> - reinit_completion(&data->done);
> - io_sqe_files_set_node(data, backup_node);
> - return ret;
> - }
> + if (ret < 0)
> + break;
> } while (1);
> + if (locked)
> + mutex_lock(&ctx->uring_lock);
> +
> + if (ret < 0) {
> + percpu_ref_resurrect(&data->refs);
> + reinit_completion(&data->done);
> + io_sqe_files_set_node(data, backup_node);
> + return ret;
> + }
>
> __io_sqe_files_unregister(ctx);
> nr_tables = DIV_ROUND_UP(ctx->nr_user_files, IORING_MAX_FILES_TABLE);
>

--
Pavel Begunkov