Re: [PATCH] io_uring/net: punt IORING_OP_BIND async if it needs file create

Jens Axboe <[email protected]> writes:

> For two reasons:
>
> 1) An opcode cannot block inside io_uring_enter() doing submissions, as
>    it'll stall the submission side pipeline.
>
> 2) Ending up in sb_start_write() -> __sb_start_write() ->
>    percpu_down_read_freezable() introduces a new lockdep edge, which it
>    correctly complains about.
>
> Check if the socket type is AF_UNIX and has a non-empty pathname. If it
> does, mark it REQ_F_FORCE_ASYNC to punt the submission to io-wq rather
> than attempt to do it inline.
>
> Fixes: 7481fd93fa0a ("io_uring: Introduce IORING_OP_BIND")
> Signed-off-by: Jens Axboe <[email protected]>
>
> ---
>
> diff --git a/io_uring/net.c b/io_uring/net.c
> index 30cd22c0b934..1f5fd8c37a5a 100644
> --- a/io_uring/net.c
> +++ b/io_uring/net.c
> @@ -4,6 +4,7 @@
>  #include <linux/file.h>
>  #include <linux/slab.h>
>  #include <linux/net.h>
> +#include <linux/un.h>
>  #include <linux/compat.h>
>  #include <net/compat.h>
>  #include <linux/io_uring.h>
> @@ -1799,11 +1800,29 @@ int io_connect(struct io_kiocb *req, unsigned int issue_flags)
>  	return IOU_COMPLETE;
>  }
>  
> +/*
> + * Check if bind request would potentiall end up with filename_create(),

potentially

> + * which in turn end up in mnt_want_write() which will grab the fs
> + * percpu start write sem. This can trigger a lockdep warning.
> + */
> +static int io_bind_file_create(const struct io_async_msghdr *io, int addr_len)
> +{
> +	const struct sockaddr_un *sun;
> +
> +	if (io->addr.ss_family != AF_UNIX)
> +		return 0;
> +	if (addr_len <= offsetof(struct sockaddr_un, sun_path))
> +		return 0;
> +	sun = (const struct sockaddr_un *) &io->addr;
> +	return sun->sun_path[0] != '\0';
> +}
> +
>  int io_bind_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  {
>  	struct io_bind *bind = io_kiocb_to_cmd(req, struct io_bind);
>  	struct sockaddr __user *uaddr;
>  	struct io_async_msghdr *io;
> +	int ret;
>  
>  	if (sqe->len || sqe->buf_index || sqe->rw_flags || sqe->splice_fd_in)
>  		return -EINVAL;
> @@ -1814,7 +1833,12 @@ int io_bind_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  	io = io_msg_alloc_async(req);
>  	if (unlikely(!io))
>  		return -ENOMEM;
> -	return move_addr_to_kernel(uaddr, bind->addr_len, &io->addr);
> +	ret = move_addr_to_kernel(uaddr, bind->addr_len, &io->addr);
> +	if (unlikely(ret))
> +		return ret;
> +	if (io_bind_file_create(io, bind->addr_len))
> +		req->flags |= REQ_F_FORCE_ASYNC;
> +	return 0;
>  }

Patch looks ok. I will add a TODO to myself to look into the bind call
getting a flag and returning -EWOULDBLOCK, so we can eventually drop the
workaround.

Reviewed-by: Gabriel Krisman Bertazi <[email protected]>


>  
>  int io_bind(struct io_kiocb *req, unsigned int issue_flags)

-- 
Gabriel Krisman Bertazi