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SubjectRe: [PATCH v6 3/3] io_uring: allow disabling rings during the creation
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On 9/8/20 7:44 AM, Stefano Garzarella wrote:
> Hi Jens,
>
> On Thu, Aug 27, 2020 at 04:58:31PM +0200, Stefano Garzarella wrote:
>> This patch adds a new IORING_SETUP_R_DISABLED flag to start the
>> rings disabled, allowing the user to register restrictions,
>> buffers, files, before to start processing SQEs.
>>
>> When IORING_SETUP_R_DISABLED is set, SQE are not processed and
>> SQPOLL kthread is not started.
>>
>> The restrictions registration are allowed only when the rings
>> are disable to prevent concurrency issue while processing SQEs.
>>
>> The rings can be enabled using IORING_REGISTER_ENABLE_RINGS
>> opcode with io_uring_register(2).
>>
>> Suggested-by: Jens Axboe <axboe@kernel.dk>
>> Reviewed-by: Kees Cook <keescook@chromium.org>
>> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>> ---
>> v4:
>> - fixed io_uring_enter() exit path when ring is disabled
>>
>> v3:
>> - enabled restrictions only when the rings start
>>
>> RFC v2:
>> - removed return value of io_sq_offload_start()
>> ---
>> fs/io_uring.c | 52 ++++++++++++++++++++++++++++++-----
>> include/uapi/linux/io_uring.h | 2 ++
>> 2 files changed, 47 insertions(+), 7 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 5f62997c147b..b036f3373fbe 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -226,6 +226,7 @@ struct io_restriction {
>> DECLARE_BITMAP(sqe_op, IORING_OP_LAST);
>> u8 sqe_flags_allowed;
>> u8 sqe_flags_required;
>> + bool registered;
>> };
>>
>> struct io_ring_ctx {
>> @@ -7497,8 +7498,8 @@ static int io_init_wq_offload(struct io_ring_ctx *ctx,
>> return ret;
>> }
>>
>> -static int io_sq_offload_start(struct io_ring_ctx *ctx,
>> - struct io_uring_params *p)
>> +static int io_sq_offload_create(struct io_ring_ctx *ctx,
>> + struct io_uring_params *p)
>> {
>> int ret;
>>
>> @@ -7532,7 +7533,6 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
>> ctx->sqo_thread = NULL;
>> goto err;
>> }
>> - wake_up_process(ctx->sqo_thread);
>> } else if (p->flags & IORING_SETUP_SQ_AFF) {
>> /* Can't have SQ_AFF without SQPOLL */
>> ret = -EINVAL;
>> @@ -7549,6 +7549,12 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
>> return ret;
>> }
>>
>> +static void io_sq_offload_start(struct io_ring_ctx *ctx)
>> +{
>> + if ((ctx->flags & IORING_SETUP_SQPOLL) && ctx->sqo_thread)
>> + wake_up_process(ctx->sqo_thread);
>> +}
>> +
>> static inline void __io_unaccount_mem(struct user_struct *user,
>> unsigned long nr_pages)
>> {
>> @@ -8295,6 +8301,9 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
>> if (!percpu_ref_tryget(&ctx->refs))
>> goto out_fput;
>>
>> + if (ctx->flags & IORING_SETUP_R_DISABLED)
>> + goto out_fput;
>> +
>
> While writing the man page paragraph, I discovered that if the rings are
> disabled I returned ENXIO error in io_uring_enter(), coming from the previous
> check.
>
> I'm not sure it is the best one, maybe I can return EBADFD or another
> error.
>
> What do you suggest?

EBADFD seems indeed the most appropriate - the fd is valid, but not in the
right state to do this.

> I'll add a test for this case.

Thanks!

--
Jens Axboe

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