unshare_test: set nr_open using soft limit

Commit Message

lufei March 28, 2025, 2:47 p.m. UTC

Set maximum file descriptor number limit by rlimit.rlim_max than
nr_open(hard limit). Hard limit may cause dup2 fail.

Signed-off-by: lufei <[e-mail]>
---
 tools/testing/selftests/core/unshare_test.c | 28 +++++++++++++--------
 1 file changed, 18 insertions(+), 10 deletions(-)

Patch

diff --git a/tools/testing/selftests/core/unshare_test.c b/tools/testing/selftests/core/unshare_test.c
index 7fec9dfb1b0e..2c4e7104b0d9 100644
--- a/tools/testing/selftests/core/unshare_test.c
+++ b/tools/testing/selftests/core/unshare_test.c
@@ -26,10 +26,11 @@  TEST(unshare_EMFILE)
 		.exit_signal = SIGCHLD,
 	};
 	int fd;
-	ssize_t n, n2;
-	static char buf[512], buf2[512];
+	ssize_t n, n2, n3;
+	static char buf[512], buf2[512], buf3[512];
 	struct rlimit rlimit;
 	int nr_open;
+	int rlimit_max;
 
 	fd = open("/proc/sys/fs/nr_open", O_RDWR);
 	ASSERT_GE(fd, 0);
@@ -42,22 +43,24 @@  TEST(unshare_EMFILE)
 
 	ASSERT_EQ(0, getrlimit(RLIMIT_NOFILE, &rlimit));
 
-	/* bump fs.nr_open */
-	n2 = sprintf(buf2, "%d\n", nr_open + 1024);
+	rlimit_max = rlimit.rlim_max;
+
+	/* bump rlimit.rlim_max */
+	n2 = sprintf(buf2, "%d\n", rlimit_max + 1024);
 	lseek(fd, 0, SEEK_SET);
 	write(fd, buf2, n2);
 
 	/* bump ulimit -n */
-	rlimit.rlim_cur = nr_open + 1024;
-	rlimit.rlim_max = nr_open + 1024;
+	rlimit.rlim_cur = rlimit_max + 1024;
+	rlimit.rlim_max = rlimit_max + 1024;
 	EXPECT_EQ(0, setrlimit(RLIMIT_NOFILE, &rlimit)) {
 		lseek(fd, 0, SEEK_SET);
 		write(fd, buf, n);
 		exit(EXIT_FAILURE);
 	}
 
-	/* get a descriptor past the old fs.nr_open */
-	EXPECT_GE(dup2(2, nr_open + 64), 0) {
+	/* get a descriptor past the old rlimit.rlim_max */
+	EXPECT_GE(dup2(2, rlimit_max + 64), 0) {
 		lseek(fd, 0, SEEK_SET);
 		write(fd, buf, n);
 		exit(EXIT_FAILURE);
@@ -74,15 +77,20 @@  TEST(unshare_EMFILE)
 	if (pid == 0) {
 		int err;
 
-		/* restore fs.nr_open */
+		n3 = sprintf(buf3, "%d\n", rlimit_max);
 		lseek(fd, 0, SEEK_SET);
-		write(fd, buf, n);
+		write(fd, buf3, n3);
+
 		/* ... and now unshare(CLONE_FILES) must fail with EMFILE */
 		err = unshare(CLONE_FILES);
 		EXPECT_EQ(err, -1)
 			exit(EXIT_FAILURE);
 		EXPECT_EQ(errno, EMFILE)
 			exit(EXIT_FAILURE);
+
+		/* restore fs.nr_open */
+		lseek(fd, 0, SEEK_SET);
+		write(fd, buf, n);
 		exit(EXIT_SUCCESS);
 	}