Read /proc/config.gz into a buffer whose first page is backed by userfaultfd and unload configs.ko while procfs copies what was read to userspace:
- removing the entry doesn't wait for the reader - the reader still gets the page that was read before the removal, and nothing more - and the next read fails with -EIO The test loads configs.ko if it isn't there, skips if configs is built in or can't be unloaded, and loads it again afterwards. It needs CONFIG_IKCONFIG=m. kselftest-merge keeps the =y that other fragments ask for, so it skips there. Signed-off-by: Christian Brauner (Amutable) <[email protected]> --- tools/testing/selftests/proc/.gitignore | 1 + tools/testing/selftests/proc/Makefile | 1 + tools/testing/selftests/proc/config | 4 + .../proc/proc-remove-slow-config-reader.c | 157 +++++++++++++++++++++ 4 files changed, 163 insertions(+) diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore index 51969f81afc5..ed3f28652bb7 100644 --- a/tools/testing/selftests/proc/.gitignore +++ b/tools/testing/selftests/proc/.gitignore @@ -25,6 +25,7 @@ /proc-remove-slow-reader /proc-remove-slow-readlink /proc-remove-slow-writer +/proc-remove-slow-config-reader /read /self /setns-dcache diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile index aecec6b93173..adbb4b1e9e9e 100644 --- a/tools/testing/selftests/proc/Makefile +++ b/tools/testing/selftests/proc/Makefile @@ -36,5 +36,6 @@ TEST_GEN_PROGS += proc-remove-slow-sysctl TEST_GEN_PROGS += proc-remove-slow-reader TEST_GEN_PROGS += proc-remove-slow-readlink TEST_GEN_PROGS += proc-remove-slow-writer +TEST_GEN_PROGS += proc-remove-slow-config-reader include ../lib.mk diff --git a/tools/testing/selftests/proc/config b/tools/testing/selftests/proc/config index c7c61a2d7927..8f672a8b49a8 100644 --- a/tools/testing/selftests/proc/config +++ b/tools/testing/selftests/proc/config @@ -8,3 +8,7 @@ CONFIG_SND_DUMMY=m CONFIG_SCSI=y CONFIG_SCSI_PROC_FS=y CONFIG_SCSI_DEBUG=m +CONFIG_MODULES=y +CONFIG_MODULE_UNLOAD=y +CONFIG_IKCONFIG=m +CONFIG_IKCONFIG_PROC=y diff --git a/tools/testing/selftests/proc/proc-remove-slow-config-reader.c b/tools/testing/selftests/proc/proc-remove-slow-config-reader.c new file mode 100644 index 000000000000..5f7bcb27b315 --- /dev/null +++ b/tools/testing/selftests/proc/proc-remove-slow-config-reader.c @@ -0,0 +1,157 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * A read that faults while procfs copies it to userspace must not hold up + * removal of the /proc entry. Unloading configs.ko removes /proc/config.gz, + * which isn't a seq_file. + */ +#define _GNU_SOURCE +#include <errno.h> +#include <fcntl.h> +#include <linux/userfaultfd.h> +#include <poll.h> +#include <pthread.h> +#include <stdlib.h> +#include <string.h> +#include <sys/ioctl.h> +#include <sys/mman.h> +#include <sys/syscall.h> +#include <unistd.h> + +#include "../kselftest_harness.h" + +#define CONFIG_PATH "/proc/config.gz" +#define CONFIG_MODULE "/sys/module/configs" +#define READ_PAGES 2 +#define TIMEOUT_MS 5000 + +struct reader { + int fd; + char *buf; + size_t len; + ssize_t ret; +}; + +struct unloader { + int done; + int ret; +}; + +static void *read_thread(void *arg) +{ + struct reader *r = arg; + + r->ret = read(r->fd, r->buf, r->len); + return NULL; +} + +static void *unload_thread(void *arg) +{ + struct unloader *u = arg; + ssize_t ret; + + u->ret = syscall(__NR_delete_module, "configs", O_NONBLOCK) ? -errno : 0; + ret = write(u->done, "x", 1); + return (void *)ret; +} + +FIXTURE(configs) { + bool loaded; +}; + +FIXTURE_SETUP(configs) +{ + self->loaded = false; + if (access(CONFIG_PATH, R_OK) && system("modprobe -q configs")) + SKIP(return, "no " CONFIG_PATH); + if (access(CONFIG_PATH, R_OK)) + SKIP(return, CONFIG_PATH ": %s", strerror(errno)); + if (access(CONFIG_MODULE, F_OK)) + SKIP(return, "configs isn't a module"); + self->loaded = true; +} + +FIXTURE_TEARDOWN(configs) +{ + /* an ASSERT may have fired with the module unloaded */ + if (self->loaded && access(CONFIG_PATH, F_OK) && + system("modprobe -q configs")) + TH_LOG("couldn't load configs again"); +} + +TEST_F(configs, remove_while_reader_faults) +{ + struct uffdio_api api = { .api = UFFD_API }; + struct uffdio_register reg = {}; + struct uffdio_zeropage zero = {}; + long psz = sysconf(_SC_PAGESIZE); + struct unloader u = {}; + struct reader r = {}; + struct uffd_msg msg; + struct pollfd pfd; + pthread_t rt, ut; + int uffd, done[2]; + char *buf, *ref; + ssize_t ref_len; + + r.fd = open(CONFIG_PATH, O_RDONLY | O_CLOEXEC); + ASSERT_GE(r.fd, 0); + + /* what the first page of a read looks like */ + ref = malloc(psz); + ASSERT_NE(ref, NULL); + ref_len = pread(r.fd, ref, psz, 0); + ASSERT_GT(ref_len, 0); + + uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK); + if (uffd < 0) + SKIP(return, "userfaultfd: %s", strerror(errno)); + ASSERT_EQ(ioctl(uffd, UFFDIO_API, &api), 0); + + /* Only the first page of the buffer goes through userfaultfd. */ + buf = mmap(NULL, READ_PAGES * psz, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + ASSERT_NE(buf, MAP_FAILED); + reg.range.start = (unsigned long)buf; + reg.range.len = psz; + reg.mode = UFFDIO_REGISTER_MODE_MISSING; + ASSERT_EQ(ioctl(uffd, UFFDIO_REGISTER, ®), 0); + + r.buf = buf; + r.len = READ_PAGES * psz; + ASSERT_EQ(pthread_create(&rt, NULL, read_thread, &r), 0); + + /* The reader now sleeps in the copy to userspace. */ + pfd = (struct pollfd){ .fd = uffd, .events = POLLIN }; + ASSERT_EQ(poll(&pfd, 1, TIMEOUT_MS), 1); + ASSERT_EQ(read(uffd, &msg, sizeof(msg)), sizeof(msg)); + ASSERT_EQ(msg.event, UFFD_EVENT_PAGEFAULT); + + /* Unloading configs.ko removes the file that is being read. */ + ASSERT_EQ(pipe2(done, O_CLOEXEC), 0); + u.done = done[1]; + ASSERT_EQ(pthread_create(&ut, NULL, unload_thread, &u), 0); + pfd = (struct pollfd){ .fd = done[0], .events = POLLIN }; + EXPECT_EQ(poll(&pfd, 1, TIMEOUT_MS), 1) { + TH_LOG("removing " CONFIG_PATH " waited for the reader"); + } + + zero.range.start = (unsigned long)buf; + zero.range.len = psz; + ASSERT_EQ(ioctl(uffd, UFFDIO_ZEROPAGE, &zero), 0); + ASSERT_EQ(pthread_join(rt, NULL), 0); + ASSERT_EQ(pthread_join(ut, NULL), 0); + if (u.ret) + SKIP(return, "unloading configs: %s", strerror(-u.ret)); + + /* + * The page that was read before the removal still arrives and the + * next piece isn't filled anymore, then nothing. + */ + EXPECT_EQ(r.ret, ref_len); + EXPECT_EQ(memcmp(buf, ref, ref_len), 0); + EXPECT_EQ(read(r.fd, buf, psz), -1); + EXPECT_EQ(errno, EIO); + free(ref); +} + +TEST_HARNESS_MAIN -- 2.53.0
