From 2e53c4e1c807d91dc7241c2104e69ad9d2c71e48 Mon Sep 17 00:00:00 2001 From: "Joel Fernandes (Google)" Date: Sat, 30 Nov 2019 17:53:31 -0800 Subject: memfd: add test for COW on MAP_PRIVATE and F_SEAL_FUTURE_WRITE mappings In this test, the parent and child both have writable private mappings. The test shows that without the patch in this series, the parent and child shared the same memory which is incorrect. In other words, COW needs to be triggered so any writes to child's copy stays local to the child. Link: http://lkml.kernel.org/r/20191107195355.80608-2-joel@joelfernandes.org Signed-off-by: Joel Fernandes (Google) Cc: Hugh Dickins Cc: Nicolas Geoffray Cc: Shuah Khan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- tools/testing/selftests/memfd/memfd_test.c | 36 ++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) (limited to 'tools') diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c index c67d32eeb668..334a7eea2004 100644 --- a/tools/testing/selftests/memfd/memfd_test.c +++ b/tools/testing/selftests/memfd/memfd_test.c @@ -290,6 +290,40 @@ static void mfd_assert_read_shared(int fd) munmap(p, mfd_def_size); } +static void mfd_assert_fork_private_write(int fd) +{ + int *p; + pid_t pid; + + p = mmap(NULL, + mfd_def_size, + PROT_READ | PROT_WRITE, + MAP_PRIVATE, + fd, + 0); + if (p == MAP_FAILED) { + printf("mmap() failed: %m\n"); + abort(); + } + + p[0] = 22; + + pid = fork(); + if (pid == 0) { + p[0] = 33; + exit(0); + } else { + waitpid(pid, NULL, 0); + + if (p[0] != 22) { + printf("MAP_PRIVATE copy-on-write failed: %m\n"); + abort(); + } + } + + munmap(p, mfd_def_size); +} + static void mfd_assert_write(int fd) { ssize_t l; @@ -760,6 +794,8 @@ static void test_seal_future_write(void) mfd_assert_read_shared(fd2); mfd_fail_write(fd2); + mfd_assert_fork_private_write(fd); + munmap(p, mfd_def_size); close(fd2); close(fd); -- cgit v1.2.3