Re: [RFC 1/1] io_uring: use valid mm in io_req_work_grab_env() in SQPOLL mode

[Pavel Begunkov <asml.silence@gmail.com>]

On 20/06/2020 02:57, Bijan Mottahedeh wrote:
> If current->mm is not set in SQPOLL mode, then use ctx->sqo_mm;
> otherwise fail thre request.

io_sq_thread_acquire_mm() called from io_async_buf_retry() should've
guaranteed presence of current->mm. Though, the problem could be in
"io_op_defs[req->opcode].needs_mm" check there, which is done only
for the first request in a link.

> 
> Signed-off-by: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>
> ---
>  fs/io_uring.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index cb696ab..fd53ea6 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -1062,8 +1062,18 @@ static inline void io_req_work_grab_env(struct io_kiocb *req,
>  					const struct io_op_def *def)
>  {
>  	if (!req->work.mm && def->needs_mm) {
> -		mmgrab(current->mm);
> -		req->work.mm = current->mm;
> +		struct mm_struct *mm = current->mm;
> +
> +		if (!mm) {
> +			if (req->ctx && req->ctx->sqo_thread)
> +				mm = req->ctx->sqo_mm;
> +			else
> +				req->work.flags |= IO_WQ_WORK_CANCEL;
> +		}
> +		if (mm) {
> +			mmgrab(mm);
> +			req->work.mm = mm;
> +		}
>  	}
>  	if (!req->work.creds)
>  		req->work.creds = get_current_cred();
> 

-- 
Pavel Begunkov