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b=ZfP/KahwDm10wm2TSGrtLVkg7xDUNnpz+rBBaInyM45cZNagos2iYqnrDed5HxIBA K+//mFWxDsWpOWe9Buj12+quSzkpcQzj2ngYZ9ZsEW0oSIiCRi7l1s6PLMfANxGQPz ES6j9Tp68ZCoex9QLLCdMUr2RP+/gA7nMafoF8zKWkoSoj6HU61hIGfIek8HtzVsMz WP7zxeoWb2ywthOOE6hEK8rHNlm6c5T599z/Oyvz7z8nNJFpq2Xxjua62S/Ez/3caV aKvdxGOQzTpkPCeB1AmIzk8MgvSvtRVAT8gs8GThhJQslYhMWBFvphDQuEoGKj/fJB b5NG8uh8YTrhw== From: Christian Brauner Date: Mon, 02 Nov 2026 15:43:29 +0100 Subject: [PATCH RFC 38/38] selftests/proc: check that a faulting readlink() doesn't hold up removal X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261102-work-procfs-bugfixes-v1-38-59422ed3e465@kernel.org> References: <20261102-work-procfs-bugfixes-v1-0-59422ed3e465@kernel.org> In-Reply-To: <20261102-work-procfs-bugfixes-v1-0-59422ed3e465@kernel.org> To: linux-fsdevel@vger.kernel.org Cc: Linus Torvalds , Jann Horn , Josef Bacik , Chris Mason , Jeff Layton , NeilBrown , Eric Dumazet , Thomas Gleixner , Al Viro , Jonathan Corbet , Christoph Hellwig , Greg Kroah-Hartman , Joel Granados , Kees Cook , Jan Kara , Jan Kara , linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, linux-um@lists.infradead.org, linux-wireless@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, ntfs3@lists.linux.dev, platform-driver-x86@vger.kernel.org, coreteam@netfilter.org, kexec@lists.infradead.org, linux-pci@vger.kernel.org, linux-sound@vger.kernel.org, netfilter-devel@vger.kernel.org, dri-devel@lists.freedesktop.org, ibm-acpi-devel@lists.sourceforge.net, jfs-discussion@lists.sourceforge.net, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-cifs@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-mm@kvack.org, linux-sh@vger.kernel.org, linux-usb@vger.kernel.org, samba-technical@lists.samba.org, sparclinux@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-doc@vger.kernel.org, linux-serial@vger.kernel.org, linux-atm-general@lists.sourceforge.net, Takashi Iwai , linux-input@vger.kernel.org, linux-raid@vger.kernel.org, linux-ext4@vger.kernel.org, linux-modules@vger.kernel.org, linux-debuggers@vger.kernel.org, "Christian Brauner (Amutable)" , Chuck Lever X-Mailer: b4 0.17-dev X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 08E8C1C0007 X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: jyouxpwp8fg7x9ezr3cdxf6u5mojmccf X-HE-Tag: 1793630833-607291 X-HE-Meta: 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 4f9qqamR PzPWjdQ9+K4kf69bBROTI+VmmgEybLzCfvMgIzceUbwCDUuQUWMZ7gj3ELWKLUw+dpbHa1YDqrOWXp9OAjg1dYIb+N1f0DwyVNNGN/xyB7xORsL6uAaEGqOEVPGkVBsRHyCkcP4wPgDl9sM8jlzEwmZ9bTSIGbKDNHyMaQkMN+RINS5GLmx0ttcud9WfLjRWc+aUwWqkEpvIu/B1FzELA7WSmfFcRI7eJLA1WTZswbpoHuygZiNh3rLyb6ccjwbcwhc0pTnCaCVKdRNFX7odTgzwUsAfRXt/+KVXQ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Add the symlink case: - readlink() /proc/asound/ of a dummy card into a buffer backed by userfaultfd - change the card's id through sysfs while the reader faults, which removes the symlink with snd_card_mutex and info_mutex held - expect that to finish without waiting for the reader Skipped without snd-dummy. Signed-off-by: Christian Brauner (Amutable) --- tools/testing/selftests/proc/.gitignore | 2 + tools/testing/selftests/proc/Makefile | 2 + tools/testing/selftests/proc/config | 3 + .../selftests/proc/proc-remove-slow-readlink.c | 191 +++++++++++++++++++++ 4 files changed, 198 insertions(+) diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore index 7b8133492782..e2566cc0ae07 100644 --- a/tools/testing/selftests/proc/.gitignore +++ b/tools/testing/selftests/proc/.gitignore @@ -22,6 +22,8 @@ /proc-uptime-002 /proc-pidns /proc-remove-slow-sysctl +/proc-remove-slow-reader +/proc-remove-slow-readlink /read /self /setns-dcache diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile index bce6beca7274..6a9bdc999f54 100644 --- a/tools/testing/selftests/proc/Makefile +++ b/tools/testing/selftests/proc/Makefile @@ -33,5 +33,7 @@ TEST_GEN_PROGS += proc-fsconfig-hidepid TEST_GEN_PROGS += proc-sysctl-readdir-churn 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 include ../lib.mk diff --git a/tools/testing/selftests/proc/config b/tools/testing/selftests/proc/config index 3edd3c437fe4..7b0e1d9be1a2 100644 --- a/tools/testing/selftests/proc/config +++ b/tools/testing/selftests/proc/config @@ -2,3 +2,6 @@ CONFIG_PROC_FS=y CONFIG_IPV6=y CONFIG_TUN=y CONFIG_USERFAULTFD=y +CONFIG_SOUND=y +CONFIG_SND=y +CONFIG_SND_DUMMY=m diff --git a/tools/testing/selftests/proc/proc-remove-slow-readlink.c b/tools/testing/selftests/proc/proc-remove-slow-readlink.c new file mode 100644 index 000000000000..3290225daecd --- /dev/null +++ b/tools/testing/selftests/proc/proc-remove-slow-readlink.c @@ -0,0 +1,191 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * A readlink() that faults while copying out the link must not hold up + * removal of the /proc symlink. Changing a sound card's id removes + * /proc/asound/ with snd_card_mutex and info_mutex held. + */ +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "../kselftest_harness.h" + +#define CARD_ID "Dummy" +#define NEW_ID "procslow" +#define LINK_PATH "/proc/asound/" CARD_ID +#define TIMEOUT_MS 5000 + +struct reader { + char *buf; + size_t len; + ssize_t ret; +}; + +struct renamer { + const char *id_path; + const char *id; + int done; + int ret; +}; + +static void *readlink_thread(void *arg) +{ + struct reader *r = arg; + + r->ret = readlink(LINK_PATH, r->buf, r->len); + return NULL; +} + +/* a new id removes the card's old /proc/asound/ link */ +static int set_id(const char *id_path, const char *id) +{ + int fd, ret; + + fd = open(id_path, O_WRONLY | O_CLOEXEC); + if (fd < 0) + return -errno; + ret = write(fd, id, strlen(id)) < 0 ? -errno : 0; + close(fd); + return ret; +} + +static void *rename_thread(void *arg) +{ + struct renamer *r = arg; + ssize_t ret; + + r->ret = set_id(r->id_path, r->id); + ret = write(r->done, "x", 1); + return (void *)ret; +} + +/* the sysfs id file of the card with @id */ +static int find_card(const char *id, char *id_path, size_t size) +{ + struct dirent *d; + int ret = -1; + DIR *dir; + + dir = opendir("/sys/class/sound"); + if (!dir) + return -1; + while (ret && (d = readdir(dir))) { + char cur[32]; + FILE *f; + + if (strncmp(d->d_name, "card", 4)) + continue; + snprintf(id_path, size, "/sys/class/sound/%s/id", d->d_name); + f = fopen(id_path, "r"); + if (!f) + continue; + if (fgets(cur, sizeof(cur), f)) { + cur[strcspn(cur, "\n")] = '\0'; + if (!strcmp(cur, id)) + ret = 0; + } + fclose(f); + } + closedir(dir); + return ret; +} + +FIXTURE(dummy) { + char id_path[PATH_MAX]; + bool renamed; +}; + +FIXTURE_SETUP(dummy) +{ + self->renamed = false; + if (access(LINK_PATH, F_OK) && system("modprobe -q snd-dummy")) + SKIP(return, "no snd-dummy"); + if (access(LINK_PATH, F_OK)) + SKIP(return, LINK_PATH ": %s", strerror(errno)); + if (find_card(CARD_ID, self->id_path, sizeof(self->id_path))) + SKIP(return, "no sysfs id file for " CARD_ID); + if (access(self->id_path, W_OK)) + SKIP(return, "%s: %s", self->id_path, strerror(errno)); +} + +FIXTURE_TEARDOWN(dummy) +{ + if (self->renamed && set_id(self->id_path, CARD_ID)) + TH_LOG("couldn't name the card " CARD_ID " again"); +} + +TEST_F(dummy, remove_while_readlink_faults) +{ + struct uffdio_api api = { .api = UFFD_API }; + struct uffdio_register reg = {}; + struct uffdio_zeropage zero = {}; + long psz = sysconf(_SC_PAGESIZE); + struct renamer rn = {}; + struct reader r = {}; + struct uffd_msg msg; + struct pollfd pfd; + pthread_t rt, nt; + int uffd, done[2]; + char *buf; + + 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); + + r.buf = buf; + r.len = psz; + ASSERT_EQ(pthread_create(&rt, NULL, readlink_thread, &r), 0); + + /* The reader now sleeps in the copy of the link 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); + + /* Renaming the card removes the link that is being read. */ + ASSERT_EQ(pipe2(done, O_CLOEXEC), 0); + rn.id_path = self->id_path; + rn.id = NEW_ID; + rn.done = done[1]; + self->renamed = true; + ASSERT_EQ(pthread_create(&nt, NULL, rename_thread, &rn), 0); + pfd = (struct pollfd){ .fd = done[0], .events = POLLIN }; + EXPECT_EQ(poll(&pfd, 1, TIMEOUT_MS), 1) { + TH_LOG("removing " LINK_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(nt, NULL), 0); + EXPECT_EQ(rn.ret, 0); + + /* The link was read before it went away. */ + EXPECT_GT(r.ret, 0); + EXPECT_EQ(readlink(LINK_PATH, buf, psz), -1); + EXPECT_EQ(errno, ENOENT); +} + +TEST_HARNESS_MAIN -- 2.53.0