[LU-15399] Don't restart CLI IO for IOCB_NOWAIT direct IO

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Labels: MON
• Severity: 3
• Assignee: Qian Yingjin
• Reporter: Qian Yingjin

Description

int cl_io_loop(const struct lu_env *env, struct cl_io *io)
{
	int result = 0;
	int rc = 0;

       ...
      if (result == -EAGAIN && io->ci_ndelay) {
		io->ci_need_restart = 1;
		result = 0;
	}

	if (result == 0)
		result = io->ci_result;
	RETURN(result < 0 ? result : 0);
}
EXPORT_SYMBOL(cl_io_loop);

ssize_t
generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
...
           if (iocb->ki_flags & IOCB_NOWAIT) {
			if (filemap_range_has_page(mapping, iocb->ki_pos,
						   iocb->ki_pos + count - 1))
				return -EAGAIN;
               ...

We should handle FLR mirror retry and io_uring IOCB_NOWAIT differently.

In the current code, it will restart the I/O engine loop when get -EAGAIN return code.
When io_uring with IOCB_NOWAIT flags and found there are page cache in the I/O range, we should return the -EAGAIN to the caller immediately.
Otherwise, it will Stuck in an endless loop。

Issue Links

• is related to: LU-15994 Fio io_uring failed with error=interrupted system call on Ubuntu 2204