Adding Axel on CC.
On Thu, Dec 22, 2016 at 12:37:29AM +0000, Bryan O'Donoghue wrote:
> commit 9250c0ee2626 ("greybus: Loopback_test: use poll instead of
> inotify") changes the flow of determining when to break out of a loop
> polling for loopback test completion.
>
> The clause is_complete() which determines if all tests are complete - as
> used is subject to a race condition where one of the tests has completed
> but at least one other test has not. On real hardware this typically
> doesn't present itself however in gbsim - which is a lot slower due in-part
> to a panopoly of printouts - we see that running a loopback test to more
> than one Interface in gbsim will fail in all instances printing out
> "Iteration count did not finish".
So I've ignored the user-space tool so far, but the description above
does not seem to explain why there is a race here. Could please expand
this a bit?
> We don't even need to have the poll() loop timeout tests in since the
> kernel threads themselves should eventually complete - and if not it's a
> kernel bug. A user of the tool can still terminate tests by doing a
> ctrl-c.
No, we still want to be well-behaved and time out if the test fails to
complete. Consider automatic testing. But you don't seem to be changing
any behaviour in this respect below?
> This patch fixes the race by ensuring the poll() loop waits for all active
> Interfaces to complete - as opposed to the first active Interface before
> breaking the loop.
Really? It looks to me like the current code tries to wait for
notifications on all fds before breaking the loop. Why do say its just
the first?
> Signed-off-by: Bryan O'Donoghue <pure.logic@xxxxxxxxxxxxxxxxx>
> ---
> drivers/staging/greybus/tools/loopback_test.c | 10 +---------
> 1 file changed, 1 insertion(+), 9 deletions(-)
>
> diff --git a/drivers/staging/greybus/tools/loopback_test.c b/drivers/staging/greybus/tools/loopback_test.c
> index f7f4cd6..f053d4fe 100644
> --- a/drivers/staging/greybus/tools/loopback_test.c
> +++ b/drivers/staging/greybus/tools/loopback_test.c
> @@ -747,7 +747,7 @@ static int wait_for_complete(struct loopback_test *t)
> if (t->poll_timeout.tv_sec != 0)
> ts = &t->poll_timeout;
>
> - while (1) {
> + while (!is_complete(t)) {
>
> ret = ppoll(t->fds, t->poll_count, ts, &mask_old);
> if (ret <= 0) {
> @@ -763,14 +763,6 @@ static int wait_for_complete(struct loopback_test *t)
> number_of_events++;
> }
> }
> -
> - if (number_of_events == t->poll_count)
> - break;
> - }
> -
> - if (!is_complete(t)) {
> - fprintf(stderr, "Iteration count did not finish!\n");
> - return -1;
> }
>
> return 0;
Johan
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