Add regression test for hangup on pipe operations

This tests the problem fixed by the patch
https://www.spinics.net/lists/linux-api/msg49731.html.

Signed-off-by: Marius Kittler <[email protected]>
Signed-off-by: Richard Palethorpe <[email protected]>
Reviewed-by: Richard Palethorpe <[email protected]>

[rpalethorpe: Made sure to perform the test on the final pipe which is
effected by the soft-limit kicking in. Fixed multiple
iterations. Removed comments. Printed the buffer size after soft-limit
is reached. Added git tags]

runtest/syscalls

@@ -1006,6 +1006,7 @@ pipe11 pipe11
 pipe12 pipe12
 pipe13 pipe13
 pipe14 pipe14
+pipe15 pipe15
 
 pipe2_01 pipe2_01
 pipe2_02 pipe2_02

testcases/kernel/syscalls/pipe/.gitignore

@@ -12,3 +12,4 @@
 /pipe12
 /pipe13
 /pipe14
+/pipe15

testcases/kernel/syscalls/pipe/pipe15.c

@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2023 SUSE LLC Marius Kittler <[email protected]>
+ */
+
+/*\
+ * [Description]
+ *
+ * This is a regression test for hangup on pipe operations. See
+ * https://www.spinics.net/lists/linux-api/msg49762.html for
+ * additional context. It tests that pipe operations do not block
+ * indefinitely when going to the soft limit on the total size of
+ * all pipes created by a single user.
+ */
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "tst_test.h"
+#include "tst_safe_stdio.h"
+#include "tst_safe_macros.h"
+
+static int pipe_count;
+static int *pipes;
+static char *buffer;
+
+static void run(void)
+{
+	const int *const pipe = pipes + 2 * (pipe_count - 1);
+	const int buffer_size = SAFE_FCNTL(pipe[1], F_GETPIPE_SZ);
+
+	tst_res(TINFO, "Soft-limited buffer size: %d bytes", buffer_size);
+	SAFE_WRITE(1, pipe[1], buffer, buffer_size);
+	SAFE_READ(1, pipe[0], buffer, buffer_size - 1);
+	SAFE_WRITE(1, pipe[1], buffer, 1);
+	tst_res(TPASS, "Pipe operation did not block");
+
+	SAFE_READ(1, pipe[0], buffer, 2);
+}
+
+static void setup(void)
+{
+	int pipe[2];
+	int page_size = getpagesize(), soft_limit;
+	struct rlimit nfd;
+
+	SAFE_PIPE(pipe);
+	const int buffer_size = SAFE_FCNTL(pipe[1], F_GETPIPE_SZ);
+	SAFE_CLOSE(pipe[0]);
+	SAFE_CLOSE(pipe[1]);
+
+	SAFE_FILE_SCANF("/proc/sys/fs/pipe-user-pages-soft", "%i", &soft_limit);
+	pipe_count = soft_limit * page_size / buffer_size;
+
+	tst_res(TINFO, "Soft limit for pipes: %i pages", soft_limit);
+	tst_res(TINFO, "Buffer size: %d byte", buffer_size);
+	tst_res(TINFO, "Creating %i pipes", pipe_count);
+
+	SAFE_GETRLIMIT(RLIMIT_NOFILE, &nfd);
+	if (nfd.rlim_max < (unsigned long)pipe_count)
+		tst_brk(TCONF, "NOFILE limit max too low: %lu < %i", nfd.rlim_max, pipe_count);
+	if (nfd.rlim_cur < nfd.rlim_max) {
+		nfd.rlim_cur = nfd.rlim_max;
+		SAFE_SETRLIMIT(RLIMIT_NOFILE, &nfd);
+	}
+
+	buffer = SAFE_MALLOC(buffer_size);
+	pipes = SAFE_MALLOC(pipe_count * 2 * sizeof(int));
+	for (int i = 0; i < pipe_count; ++i)
+		SAFE_PIPE(pipes + i * 2);
+
+}
+
+static void cleanup(void)
+{
+	for (int i = 0; i < pipe_count * 2; i++)
+		if (pipes[i] > 0)
+			SAFE_CLOSE(pipes[i]);
+	if (pipes)
+		free(pipes);
+	if (buffer)
+		free(buffer);
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.test_all = run,
+	.cleanup = cleanup,
+	.tags = (const struct tst_tag[]){
+		{"linux-git", "46c4c9d1beb7"},
+	},
+};