Re: [PATCH v4 1/2] io_uring: avoid whole io_wq_work copy for requests completed inline

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

>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 12296ce3e8b9..2a3a02838f7b 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -907,9 +907,10 @@ static void io_file_put_work(struct work_struct *work);
>>   static inline void io_req_init_async(struct io_kiocb *req,
>>                          void (*func)(struct io_wq_work **))
>>   {
>> -       if (req->flags & REQ_F_WORK_INITIALIZED)
>> -               req->work.func = func;
>> -       else {
>> +       if (req->flags & REQ_F_WORK_INITIALIZED) {
>> +               if (!req->work.func)
>> +                       req->work.func = func;
>> +       } else {
>>                  req->work = (struct io_wq_work){ .func = func };
>>                  req->flags |= REQ_F_WORK_INITIALIZED;
>>          }
>> @@ -2920,6 +2921,8 @@ static int __io_splice_prep(struct io_kiocb *req,
>>                  return ret;
>>          req->flags |= REQ_F_NEED_CLEANUP;
>>
>> +       /* Splice will be punted aync, so initialize io_wq_work firstly_*/
>> +       io_req_init_async(req, io_wq_submit_work);
>>          if (!S_ISREG(file_inode(sp->file_in)->i_mode))
>>                  req->work.flags |= IO_WQ_WORK_UNBOUND;
>>
>> @@ -3592,6 +3595,9 @@ static int io_statx(struct io_kiocb *req, bool force_nonblock)
>>
>>   static int io_close_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>>   {
>> +        /* Close may be punted aync, so initialize io_wq_work firstly */
>> +       io_req_init_async(req, io_wq_submit_work);
>> +
> For splice and close requests, these two about io_req_init_async() calls should be
> io_req_init_async(req, NULL), because they change req->work.flags firstly.

Please no. Such assumptions/dependencies are prone to break.
It'll get us subtle bugs in no time. 

BTW, why not io_wq_submit_work in place of NULL?

-- 
Pavel Begunkov