Write to /proc/scsi/scsi_debug/<host> from a buffer whose page is backed by userfaultfd and remove the host while procfs copies in what is written:
- removing the entry doesn't wait for the writer - the write fails with -EIO once the fault is resolved The test loads scsi_debug if it isn't there and skips without it. 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 | 3 + .../selftests/proc/proc-remove-slow-writer.c | 203 +++++++++++++++++++++ 4 files changed, 208 insertions(+) diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore index e2566cc0ae07..51969f81afc5 100644 --- a/tools/testing/selftests/proc/.gitignore +++ b/tools/testing/selftests/proc/.gitignore @@ -24,6 +24,7 @@ /proc-remove-slow-sysctl /proc-remove-slow-reader /proc-remove-slow-readlink +/proc-remove-slow-writer /read /self /setns-dcache diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile index 6a9bdc999f54..aecec6b93173 100644 --- a/tools/testing/selftests/proc/Makefile +++ b/tools/testing/selftests/proc/Makefile @@ -35,5 +35,6 @@ TEST_GEN_PROGS += proc-pidns 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 include ../lib.mk diff --git a/tools/testing/selftests/proc/config b/tools/testing/selftests/proc/config index 7b0e1d9be1a2..c7c61a2d7927 100644 --- a/tools/testing/selftests/proc/config +++ b/tools/testing/selftests/proc/config @@ -5,3 +5,6 @@ CONFIG_USERFAULTFD=y CONFIG_SOUND=y CONFIG_SND=y CONFIG_SND_DUMMY=m +CONFIG_SCSI=y +CONFIG_SCSI_PROC_FS=y +CONFIG_SCSI_DEBUG=m diff --git a/tools/testing/selftests/proc/proc-remove-slow-writer.c b/tools/testing/selftests/proc/proc-remove-slow-writer.c new file mode 100644 index 000000000000..f69ca75ba87c --- /dev/null +++ b/tools/testing/selftests/proc/proc-remove-slow-writer.c @@ -0,0 +1,203 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * A write that faults while procfs copies it in must not hold up removal of + * the /proc entry. Removing a scsi_debug host removes its + * /proc/scsi/scsi_debug/<host> file. + */ +#define _GNU_SOURCE +#include <dirent.h> +#include <errno.h> +#include <fcntl.h> +#include <limits.h> +#include <linux/userfaultfd.h> +#include <poll.h> +#include <pthread.h> +#include <stdio.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 ADD_HOST "/sys/bus/pseudo/drivers/scsi_debug/add_host" +#define HOST_DIR "/proc/scsi/scsi_debug" +#define TIMEOUT_MS 5000 +#define MAX_HOSTS 4096 +#define HOST_BITS (8 * sizeof(unsigned long)) + +struct writer { + int fd; + char *buf; + ssize_t ret; + int err; +}; + +struct remover { + int done; + int ret; +}; + +/* a positive @nr adds hosts, a negative one removes the last ones added */ +static int add_host(int nr) +{ + char s[16]; + int fd, len, ret; + + fd = open(ADD_HOST, O_WRONLY | O_CLOEXEC); + if (fd < 0) + return -errno; + len = snprintf(s, sizeof(s), "%d", nr); + ret = write(fd, s, len) == len ? 0 : -errno; + close(fd); + return ret; +} + +/* the numbers of the hosts in /proc/scsi/scsi_debug as a bitmap */ +static int list_hosts(unsigned long *hosts) +{ + struct dirent *d; + DIR *dir; + + memset(hosts, 0, MAX_HOSTS / 8); + dir = opendir(HOST_DIR); + if (!dir) + /* the directory comes with the first host and goes with the last */ + return errno == ENOENT ? 0 : -errno; + while ((d = readdir(dir))) { + char *end; + long nr = strtol(d->d_name, &end, 10); + + if (end != d->d_name && !*end && nr >= 0 && nr < MAX_HOSTS) + hosts[nr / HOST_BITS] |= 1UL << (nr % HOST_BITS); + } + closedir(dir); + return 0; +} + +/* the host that is in @after but wasn't in @before */ +static int new_host(const unsigned long *before, const unsigned long *after) +{ + for (int i = 0; i < MAX_HOSTS / HOST_BITS; i++) { + unsigned long new = after[i] & ~before[i]; + + if (new) + return i * HOST_BITS + __builtin_ctzl(new); + } + return -1; +} + +static void *write_thread(void *arg) +{ + struct writer *w = arg; + + w->ret = write(w->fd, w->buf, 2); + w->err = errno; + return NULL; +} + +static void *remove_thread(void *arg) +{ + struct remover *r = arg; + ssize_t ret; + + r->ret = add_host(-1); + ret = write(r->done, "x", 1); + return (void *)ret; +} + +FIXTURE(host) { + char path[PATH_MAX]; + int host; +}; + +FIXTURE_SETUP(host) +{ + unsigned long before[MAX_HOSTS / HOST_BITS]; + unsigned long after[MAX_HOSTS / HOST_BITS]; + + self->host = -1; + if (access(ADD_HOST, W_OK) && system("modprobe -q scsi_debug add_host=0")) + SKIP(return, "no scsi_debug"); + if (access(ADD_HOST, W_OK)) + SKIP(return, ADD_HOST ": %s", strerror(errno)); + + /* host numbers are reused, so look for the one that's new */ + ASSERT_EQ(list_hosts(before), 0); + ASSERT_EQ(add_host(1), 0); + ASSERT_EQ(list_hosts(after), 0); + self->host = new_host(before, after); + ASSERT_GE(self->host, 0); + snprintf(self->path, sizeof(self->path), HOST_DIR "/%d", self->host); +} + +FIXTURE_TEARDOWN(host) +{ + if (self->host >= 0 && !access(self->path, F_OK)) + add_host(-1); +} + +TEST_F(host, remove_while_writer_faults) +{ + struct uffdio_api api = { .api = UFFD_API }; + struct uffdio_register reg = {}; + struct uffdio_zeropage zero = {}; + long psz = sysconf(_SC_PAGESIZE); + struct writer w = {}; + struct remover r = {}; + struct uffd_msg msg; + struct pollfd pfd; + pthread_t wt, rt; + int uffd, done[2]; + char *buf; + + w.fd = open(self->path, O_WRONLY | O_CLOEXEC); + if (w.fd < 0) + SKIP(return, "%s: %s", self->path, strerror(errno)); + + 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); + + buf = mmap(NULL, 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); + + w.buf = buf; + ASSERT_EQ(pthread_create(&wt, NULL, write_thread, &w), 0); + + /* The writer now sleeps while what it writes is copied in. */ + 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); + + /* Removing the host removes the file that is being written. */ + ASSERT_EQ(pipe2(done, O_CLOEXEC), 0); + r.done = done[1]; + ASSERT_EQ(pthread_create(&rt, NULL, remove_thread, &r), 0); + pfd = (struct pollfd){ .fd = done[0], .events = POLLIN }; + EXPECT_EQ(poll(&pfd, 1, TIMEOUT_MS), 1) { + TH_LOG("removing %s waited for the writer", self->path); + } + + zero.range.start = (unsigned long)buf; + zero.range.len = psz; + ASSERT_EQ(ioctl(uffd, UFFDIO_ZEROPAGE, &zero), 0); + ASSERT_EQ(pthread_join(wt, NULL), 0); + ASSERT_EQ(pthread_join(rt, NULL), 0); + EXPECT_EQ(r.ret, 0); + + /* The entry was gone by the time the write got to it. */ + EXPECT_EQ(w.ret, -1); + EXPECT_EQ(w.err, EIO); +} + +TEST_HARNESS_MAIN -- 2.53.0
