Re: [PATCH v2 02/14] io_uring/cmd: fix tw <-> issue_flags conversion

[Jens Axboe <axboe@kernel.dk>]

On 3/17/24 8:23 PM, Ming Lei wrote:
> On Mon, Mar 18, 2024 at 12:41:47AM +0000, Pavel Begunkov wrote:
>> !IO_URING_F_UNLOCKED does not translate to availability of the deferred
>> completion infra, IO_URING_F_COMPLETE_DEFER does, that what we should
>> pass and look for to use io_req_complete_defer() and other variants.
>>
>> Luckily, it's not a real problem as two wrongs actually made it right,
>> at least as far as io_uring_cmd_work() goes.
>>
>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>> Link: https://lore.kernel.org/r/eb08e72e837106963bc7bc7dccfd93d646cc7f36.1710514702.git.asml.silence@gmail.com
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>> ---
>>  io_uring/uring_cmd.c | 10 ++++++++--
>>  1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
>> index f197e8c22965..ec38a8d4836d 100644
>> --- a/io_uring/uring_cmd.c
>> +++ b/io_uring/uring_cmd.c
>> @@ -56,7 +56,11 @@ EXPORT_SYMBOL_GPL(io_uring_cmd_mark_cancelable);
>>  static void io_uring_cmd_work(struct io_kiocb *req, struct io_tw_state *ts)
>>  {
>>  	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
>> -	unsigned issue_flags = ts->locked ? 0 : IO_URING_F_UNLOCKED;
>> +	unsigned issue_flags = IO_URING_F_UNLOCKED;
>> +
>> +	/* locked task_work executor checks the deffered list completion */
>> +	if (ts->locked)
>> +		issue_flags = IO_URING_F_COMPLETE_DEFER;
>>  
>>  	ioucmd->task_work_cb(ioucmd, issue_flags);
>>  }
>> @@ -100,7 +104,9 @@ void io_uring_cmd_done(struct io_uring_cmd *ioucmd, ssize_t ret, ssize_t res2,
>>  	if (req->ctx->flags & IORING_SETUP_IOPOLL) {
>>  		/* order with io_iopoll_req_issued() checking ->iopoll_complete */
>>  		smp_store_release(&req->iopoll_completed, 1);
>> -	} else if (!(issue_flags & IO_URING_F_UNLOCKED)) {
>> +	} else if (issue_flags & IO_URING_F_COMPLETE_DEFER) {
>> +		if (WARN_ON_ONCE(issue_flags & IO_URING_F_UNLOCKED))
>> +			return;
>>  		io_req_complete_defer(req);
>>  	} else {
>>  		req->io_task_work.func = io_req_task_complete;
> 
> 'git-bisect' shows the reported warning starts from this patch.

That does make sense, as probably:

+	/* locked task_work executor checks the deffered list completion */
+	if (ts->locked)
+		issue_flags = IO_URING_F_COMPLETE_DEFER;

this assumption isn't true, and that would mess with the task management
(which is in your oops).

-- 
Jens Axboe