[PATCH v2 1/2] src/queue: don't swallow -ETIME when SQEs were submitted

[Prateek <kprateek283@gmail.com>]

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 <kprateek283@gmail.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Prateek <kprateek283@gmail.com>
---
 src/queue.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/queue.c b/src/queue.c
index fcd3c702..e2e5a061 100644
--- a/src/queue.c
+++ b/src/queue.c
@@ -110,12 +110,12 @@ static int _io_uring_get_cqe(struct io_uring *ring,
 			 * timeout, so treat any timeout the same as -ETIME here.
 			 */
 			if (data->get_flags & IORING_ENTER_EXT_ARG_REG) {
-				if (!cqe && !err)
+				if (!cqe && err >= 0)
 					err = -ETIME;
 			} else {
 				struct io_uring_getevents_arg *arg = data->arg;
 
-				if (!cqe && arg->ts && !err)
+				if (!cqe && arg->ts && err >= 0)
 					err = -ETIME;
 			}
 			break;
-- 
2.43.0