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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=NJukzHF4; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C7542607524A; Wed, 4 Nov 2026 19:28:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=NJukzHF4 Received: by smtp.kernel.org (Postfix) with ESMTPSA id DC5AB1F000C1; Wed, 4 Nov 2026 19:28:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793820520; bh=KE0FjFLg86Wqg2LOdvIKebjks/LaCpUOq5x1mMvJN8E=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=NJukzHF4aV1KUnciVzdApjdNLx1CFG6CVAD2vCJ43JPCAnjjn1zUpxzmLM9SfrWre gCGPTz2pnkhsoLDD0ufQYz7LJbRa17CKdFnkfKWFZpzCvx3VornSWUNThr1WFvwPGn CADeWgCgoQP5K7ENKjJkvGY6u4437GknzfxpYekJnpL3cgHKr3XG5TRSEcefhaKP7V nX57prmegY0CCerzsNzag/fJkXOMUpt/ed2ZwMst0kUSU+NPQt8+F88n3teURVqhXg 7vNgcQSCorU7kpZuBp2BFO4KHe0i6WajNcx/gISK920csNZ4jtjgQF1W1PAyzKkO5E yV22BOQaWeKsQ== From: Christian Brauner 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 Subject: [PATCH RESEND v2 51/51] selftests/proc: check that a faulting readlink() doesn't hold up removal Date: Wed, 4 Nov 2026 20:28:26 +0100 Message-ID: <20261104-work-procfs-bugfixes-v2-51-021c84d852e0@kernel.org> In-Reply-To: <20261104-work-procfs-bugfixes-v2-0-021c84d852e0@kernel.org> References: <20261104-work-procfs-bugfixes-v2-0-021c84d852e0@kernel.org> X-Mailing-List: linux-debuggers@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" X-Mailer: b4 0.17-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=7257; i=brauner@kernel.org; h=from:subject:message-id; bh=tBvbDpChuad7Gf34o7zrAy5GeGJ/8Uzeoj8ryWST3Tk=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWS9buLeeHbphO3/N55kVVv59tmN3VuetO2e/UrKp4azz iWph8NwQkcpC4MYF4OsmCKLQ7tJuNxynorNRpkaMHNYmUCGMHBxCsBEjIIZ/vAeD7jB+vdim/Jj tQ0hkWc2r77GNq27cuqvPzkuqa9flfYz/NOXCS3acGvTlZz++E+JTd/e+ny6wif2bUN30YcXfYm /q1kB X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 Content-Transfer-Encoding: 8bit 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 | 1 + tools/testing/selftests/proc/Makefile | 1 + tools/testing/selftests/proc/config | 5 + .../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..3fa89f46b9c7 100644 --- a/tools/testing/selftests/proc/.gitignore +++ b/tools/testing/selftests/proc/.gitignore @@ -22,6 +22,7 @@ /proc-uptime-002 /proc-pidns /proc-remove-slow-sysctl +/proc-remove-slow-readlink /read /self /setns-dcache diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile index bce6beca7274..df02699a3587 100644 --- a/tools/testing/selftests/proc/Makefile +++ b/tools/testing/selftests/proc/Makefile @@ -33,5 +33,6 @@ 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-readlink include ../lib.mk diff --git a/tools/testing/selftests/proc/config b/tools/testing/selftests/proc/config index 052e365af5a9..1504a761b39b 100644 --- a/tools/testing/selftests/proc/config +++ b/tools/testing/selftests/proc/config @@ -3,3 +3,8 @@ CONFIG_NET_NS=y CONFIG_IPV6=y CONFIG_TUN=y CONFIG_USERFAULTFD=y +CONFIG_SOUND=y +CONFIG_SND=y +CONFIG_SND_DUMMY=m +CONFIG_MODULES=y +CONFIG_MODULE_UNLOAD=y 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