[PATCH] selftests/epoll: add a regression test for pipe->poll_usage

[PATCH] selftests/epoll: add a regression test for pipe->poll_usage

[Oleg Nesterov]

pipe->poll_usage was added to ensure that edge-triggered epoll consumers
get a wakeup on every write, even if the pipe was already non-empty.
However, none of the existing epoll_wakeup_test cases cover this; the
test suite passes even with WRITE_ONCE(pipe->poll_usage, true) removed.

Add a test that writes twice to a pipe and verifies that epoll_wait with
EPOLLET reports data each time. This covers the pipe-specific per-write
wakeup behavior that edge-triggered consumers depend on.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 .../filesystems/epoll/epoll_wakeup_test.c     | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c b/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
index f6f1a7ff01b0..6ad7905ef95a 100644
--- a/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
+++ b/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
@@ -3538,4 +3538,28 @@ TEST(epoll65)
 	close(ctx.efd[1]);
 }
 
+TEST(epoll66)
+{
+	struct epoll_event event;
+	int pfd[2], efd, err;
+
+	pipe(pfd);
+
+	efd = epoll_create1(0);
+	ASSERT_GE(efd, 0);
+
+	event.events = EPOLLIN | EPOLLET;
+	err = epoll_ctl(efd, EPOLL_CTL_ADD, pfd[0], &event);
+	ASSERT_EQ(err, 0);
+
+	for (int i = 0; i < 2; ++i) {
+		write(pfd[1], "", 1);
+		EXPECT_EQ(epoll_wait(efd, &event, 1, 0), 1);
+	}
+
+	close(pfd[0]);
+	close(pfd[1]);
+	close(efd);
+}
+
 TEST_HARNESS_MAIN
-- 
2.52.0

Re: [PATCH] selftests/epoll: add a regression test for pipe->poll_usage

[Oleg Nesterov]

Sashiko suggests to check the results of pipe() and write() as well:

	https://sashiko.dev/#/patchset/amna1QtCtqll1LFj%40redhat.com

Not sure this makes sense, but I'll send V2 just in case.

Oleg.

On 07/29, Oleg Nesterov wrote:
>
> pipe->poll_usage was added to ensure that edge-triggered epoll consumers
> get a wakeup on every write, even if the pipe was already non-empty.
> However, none of the existing epoll_wakeup_test cases cover this; the
> test suite passes even with WRITE_ONCE(pipe->poll_usage, true) removed.
> 
> Add a test that writes twice to a pipe and verifies that epoll_wait with
> EPOLLET reports data each time. This covers the pipe-specific per-write
> wakeup behavior that edge-triggered consumers depend on.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  .../filesystems/epoll/epoll_wakeup_test.c     | 24 +++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c b/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
> index f6f1a7ff01b0..6ad7905ef95a 100644
> --- a/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
> +++ b/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
> @@ -3538,4 +3538,28 @@ TEST(epoll65)
>  	close(ctx.efd[1]);
>  }
>  
> +TEST(epoll66)
> +{
> +	struct epoll_event event;
> +	int pfd[2], efd, err;
> +
> +	pipe(pfd);
> +
> +	efd = epoll_create1(0);
> +	ASSERT_GE(efd, 0);
> +
> +	event.events = EPOLLIN | EPOLLET;
> +	err = epoll_ctl(efd, EPOLL_CTL_ADD, pfd[0], &event);
> +	ASSERT_EQ(err, 0);
> +
> +	for (int i = 0; i < 2; ++i) {
> +		write(pfd[1], "", 1);
> +		EXPECT_EQ(epoll_wait(efd, &event, 1, 0), 1);
> +	}
> +
> +	close(pfd[0]);
> +	close(pfd[1]);
> +	close(efd);
> +}
> +
>  TEST_HARNESS_MAIN
> -- 
> 2.52.0
>