Re: [PATCH 1/2] src/queue: don't swallow -ETIME when SQEs were submitted

Prateek <[email protected]> writes:

> If _io_uring_get_cqe() submits SQEs and then times out waiting for
> completions, it returns the submit count instead of -ETIME:
>
>   1. The first enter submits the SQEs; because submit > 0 the kernel
>      returns the submit count, not -ETIME, and it is stored in err.
>   2. On the next iteration the has_ts shortcut wants to report -ETIME,
>      but the 'if (!err)' guard sees the non-zero submit count and keeps
>      it, so -ETIME is dropped.
>
> That contradicts io_uring_submit_and_wait_timeout(3) and
> io_uring_wait_cqes(3), which document -ETIME on timeout.
>
> At these two sites (lines 113 and 118) err is only ever 0 or a positive
> submit count. A negative error from __io_uring_peek_cqe() or a prior
> enter breaks out of the loop before reaching here. So the change is
> functionally equivalent to dropping the err condition entirely; we change
> '!err' to 'err >= 0' so -ETIME is successfully synthesized whenever no
> CQE was seen.
>
> The guards were added in 2f61e849 ("src/queue: don't wait twice if
> looping in _io_uring_get_cqe()") to carry the submit count across
> iterations for the partial-completion case (got some CQEs, no error);
> that case still returns the count because both sites remain guarded by
> !cqe.
>
> Signed-off-by: Prateek <[email protected]>


Reviewed-by: Gabriel Krisman Bertazi <[email protected]>

-- 
Gabriel Krisman Bertazi