From df0b7e0ea59c43708cff8c7e34da5e2f8d430e5e Mon Sep 17 00:00:00 2001 From: Konstantin Khorenko Date: Fri, 14 Aug 2026 18:57:09 +0200 Subject: [PATCH] selftests/core: fix unshare_test with large fs.nr_open The test assumes fs.nr_open is close to the default 1048576, but some systems set it much higher (e.g. 1073741816). This is systemd's doing: since systemd v240 (2018), PID 1 bumps fs.nr_open and fs.file-max to their largest possible values on boot, as file descriptors are already accounted for by memcg [1]. In that case, dup2() to nr_open + 64 requires the kernel to allocate a file descriptor table with ~1 billion entries, which fails with ENOMEM. On a kernel that already carries 04a2c4b4511d1, dup2() no longer fails with ENOMEM. The allocation is now rejected up front and the caller gets EMFILE instead, without the WARNING, but the test still fails. Cap the nr_open value used for the test's own arithmetic to a known reasonable base value (1048576) and restore the true original value once the test has completed. Link: https://lore.kernel.org/20260814165709.513263-1-khorenko@virtuozzo.com Link: https://github.com/systemd/systemd/commit/a8b627aaed409a15260c25988970c795bf963812 [1] Signed-off-by: Konstantin Khorenko Signed-off-by: Eva Kurchatova Signed-off-by: Andrew Morton Cc: Shuah Khan Cc: Wei Yang Cc: --- tools/testing/selftests/core/unshare_test.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/core/unshare_test.c b/tools/testing/selftests/core/unshare_test.c index ffce75a6c228..d40e963dd520 100644 --- a/tools/testing/selftests/core/unshare_test.c +++ b/tools/testing/selftests/core/unshare_test.c @@ -40,6 +40,14 @@ TEST(unshare_EMFILE) ASSERT_EQ(sscanf(buf, "%d", &nr_open), 1); + /* + * Cap nr_open for the duration of the test to avoid ENOMEM from a + * huge fd table allocation; buf/n keep the real original value so + * fs.nr_open can be restored to it once the test is done. + */ + if (nr_open > 1024 * 1024) + nr_open = 1024 * 1024; + ASSERT_EQ(0, getrlimit(RLIMIT_NOFILE, &rlimit)); /* bump fs.nr_open */ @@ -73,10 +81,13 @@ TEST(unshare_EMFILE) if (pid == 0) { int err; + char buf3[32]; + ssize_t n3; - /* restore fs.nr_open */ + /* restore fs.nr_open to the (possibly capped) test baseline */ + n3 = sprintf(buf3, "%d\n", nr_open); 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) @@ -89,6 +100,10 @@ TEST(unshare_EMFILE) EXPECT_EQ(waitpid(pid, &status, 0), pid); EXPECT_EQ(true, WIFEXITED(status)); EXPECT_EQ(0, WEXITSTATUS(status)); + + /* restore the real fs.nr_open value */ + lseek(fd, 0, SEEK_SET); + write(fd, buf, n); } TEST_HARNESS_MAIN