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Mon, 2 Nov 2026 14:46:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793630792; bh=8OUC3OpgPcYXff2v4b0WbdSVZE7XWpoJGNZRHA3e5A4=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=XWvDNXOEbgzkyZSZLEEf/fLDGQTJKwF0ltSxY/EL3lo82Mkr/aDxZgyoDMPnEDdLr 5p9X0oQCHCkY63MlXypffIH/FgWzMKVYCEo4i3pEbfJuBXE7iGAORsSWwgE8jxQhAy 4NKKegcYQITsSSiB9ubx16WR7JIBFMAtYwmdkdE/Zzf6jzzLfZ7rDbpHNZ3omVKKWs 5YTo9uoKH3WQgJg5iglu6NkXshnM4oNeVvav8v5ihPYSLjDC/W/Dnb3rFkAiPkdkb/ knAVm1KzmCTPRmBb4tIwPxCsIua2TX2REoD5qySaeeWkURDqxkkuEp88D6dK5T0/43 GCmlt6X8Ltfhw== From: Christian Brauner Date: Mon, 02 Nov 2026 15:43:27 +0100 Subject: [PATCH RFC 36/38] selftests/proc: check that faulting sysctl accesses don't hold up removal X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , Precedence: list X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261102-work-procfs-bugfixes-v1-36-59422ed3e465@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-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=unavailable autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Read, write and list /proc/sys/net/ipv6/conf// of a tun device with a buffer whose first page is backed by userfaultfd and remove the device while the task sleeps in its copy from or to userspace: - unregistering the table doesn't wait for a faulting read(), write() or getdents64() - the read still gets the value that was produced before the removal and the next read fails with -ENOENT - the write is copied in after the removal and fails with -ENOENT - getdents64() still lists what it looked up before the removal and fails with -ENOENT afterwards The tables are unregistered under RTNL, so a regression stalls each test for five seconds before it fails. Signed-off-by: Christian Brauner (Amutable) --- tools/testing/selftests/proc/.gitignore | 1 + tools/testing/selftests/proc/Makefile | 1 + tools/testing/selftests/proc/config | 3 + .../selftests/proc/proc-remove-slow-sysctl.c | 213 +++++++++++++++++++++ 4 files changed, 218 insertions(+) diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore index 5b5e24e39cbd..7b8133492782 100644 --- a/tools/testing/selftests/proc/.gitignore +++ b/tools/testing/selftests/proc/.gitignore @@ -21,6 +21,7 @@ /proc-uptime-001 /proc-uptime-002 /proc-pidns +/proc-remove-slow-sysctl /read /self /setns-dcache diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile index dae09f333455..bce6beca7274 100644 --- a/tools/testing/selftests/proc/Makefile +++ b/tools/testing/selftests/proc/Makefile @@ -32,5 +32,6 @@ TEST_GEN_PROGS += proc-multiple-procfs 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 include ../lib.mk diff --git a/tools/testing/selftests/proc/config b/tools/testing/selftests/proc/config index 68fbd2b35884..3edd3c437fe4 100644 --- a/tools/testing/selftests/proc/config +++ b/tools/testing/selftests/proc/config @@ -1 +1,4 @@ CONFIG_PROC_FS=y +CONFIG_IPV6=y +CONFIG_TUN=y +CONFIG_USERFAULTFD=y diff --git a/tools/testing/selftests/proc/proc-remove-slow-sysctl.c b/tools/testing/selftests/proc/proc-remove-slow-sysctl.c new file mode 100644 index 000000000000..e1b1fd19a07a --- /dev/null +++ b/tools/testing/selftests/proc/proc-remove-slow-sysctl.c @@ -0,0 +1,213 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * A read(), write() or getdents64() of /proc/sys that faults while copying + * from or to userspace must not hold up unregistering the sysctl table. + * /proc/sys/net/ipv6/conf// of a tun device is unregistered under RTNL + * when the device's file is closed. + */ +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "../kselftest_harness.h" + +#define TUN_NAME "procslow0" +#define CONF_PATH "/proc/sys/net/ipv6/conf/" TUN_NAME +#define MTU_PATH CONF_PATH "/mtu" +#define BUF_PAGES 16 +#define TIMEOUT_MS 5000 + +enum sysctl_op { + SYSCTL_READ, + SYSCTL_WRITE, + SYSCTL_GETDENTS, +}; + +struct worker { + enum sysctl_op op; + int fd; + char *buf; + size_t len; + ssize_t ret; + int err; +}; + +struct closer { + int tun; + int done; +}; + +static void *work_thread(void *arg) +{ + struct worker *w = arg; + + switch (w->op) { + case SYSCTL_READ: + w->ret = read(w->fd, w->buf, w->len); + break; + case SYSCTL_WRITE: + w->ret = write(w->fd, w->buf, w->len); + break; + case SYSCTL_GETDENTS: + w->ret = syscall(__NR_getdents64, w->fd, w->buf, w->len); + break; + } + w->err = errno; + return NULL; +} + +static void *close_thread(void *arg) +{ + struct closer *c = arg; + ssize_t ret; + + close(c->tun); + ret = write(c->done, "x", 1); + return (void *)ret; +} + +FIXTURE(proc_sys_slow) { + int tun; + int uffd; + char *buf; + long psz; +}; + +FIXTURE_SETUP(proc_sys_slow) +{ + struct uffdio_api api = { .api = UFFD_API }; + struct uffdio_register reg = {}; + struct ifreq ifr = {}; + + if (unshare(CLONE_NEWNET)) + SKIP(return, "unshare(CLONE_NEWNET): %s", strerror(errno)); + + self->tun = open("/dev/net/tun", O_RDWR | O_CLOEXEC); + if (self->tun < 0) + SKIP(return, "/dev/net/tun: %s", strerror(errno)); + strncpy(ifr.ifr_name, TUN_NAME, IFNAMSIZ - 1); + ifr.ifr_flags = IFF_TUN | IFF_NO_PI; + ASSERT_EQ(ioctl(self->tun, TUNSETIFF, &ifr), 0); + if (access(CONF_PATH, F_OK)) + SKIP(return, CONF_PATH ": %s", strerror(errno)); + + self->uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK); + if (self->uffd < 0) + SKIP(return, "userfaultfd: %s", strerror(errno)); + ASSERT_EQ(ioctl(self->uffd, UFFDIO_API, &api), 0); + + /* Only the first page of the buffer goes through userfaultfd. */ + self->psz = sysconf(_SC_PAGESIZE); + self->buf = mmap(NULL, BUF_PAGES * self->psz, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + ASSERT_NE(self->buf, MAP_FAILED); + reg.range.start = (unsigned long)self->buf; + reg.range.len = self->psz; + reg.mode = UFFDIO_REGISTER_MODE_MISSING; + ASSERT_EQ(ioctl(self->uffd, UFFDIO_REGISTER, ®), 0); +} + +FIXTURE_TEARDOWN(proc_sys_slow) +{ +} + +/* + * Let @w sleep in its copy from or to the first page of the buffer, then + * close the device. Unregistering the table must not wait for @w. + */ +static void stall_and_remove(struct __test_metadata *_metadata, + FIXTURE_DATA(proc_sys_slow) *self, + struct worker *w) +{ + struct closer c = { .tun = self->tun }; + struct uffdio_zeropage zero = {}; + struct uffd_msg msg; + struct pollfd pfd; + pthread_t wt, ct; + int done[2]; + + w->buf = self->buf; + ASSERT_EQ(pthread_create(&wt, NULL, work_thread, w), 0); + + pfd = (struct pollfd){ .fd = self->uffd, .events = POLLIN }; + ASSERT_EQ(poll(&pfd, 1, TIMEOUT_MS), 1); + ASSERT_EQ(read(self->uffd, &msg, sizeof(msg)), sizeof(msg)); + ASSERT_EQ(msg.event, UFFD_EVENT_PAGEFAULT); + + ASSERT_EQ(pipe2(done, O_CLOEXEC), 0); + c.done = done[1]; + ASSERT_EQ(pthread_create(&ct, NULL, close_thread, &c), 0); + pfd = (struct pollfd){ .fd = done[0], .events = POLLIN }; + EXPECT_EQ(poll(&pfd, 1, TIMEOUT_MS), 1) { + TH_LOG("unregistering " CONF_PATH " waited for the faulting task"); + } + + zero.range.start = (unsigned long)self->buf; + zero.range.len = self->psz; + ASSERT_EQ(ioctl(self->uffd, UFFDIO_ZEROPAGE, &zero), 0); + ASSERT_EQ(pthread_join(wt, NULL), 0); + ASSERT_EQ(pthread_join(ct, NULL), 0); +} + +TEST_F(proc_sys_slow, read) +{ + struct worker w = { + .op = SYSCTL_READ, + .len = BUF_PAGES * self->psz, + }; + + w.fd = open(MTU_PATH, O_RDONLY | O_CLOEXEC); + ASSERT_GE(w.fd, 0); + stall_and_remove(_metadata, self, &w); + + /* The value was produced before the table went away, then nothing. */ + EXPECT_GT(w.ret, 0); + EXPECT_EQ(read(w.fd, self->buf, self->psz), -1); + EXPECT_EQ(errno, ENOENT); +} + +TEST_F(proc_sys_slow, write) +{ + struct worker w = { + .op = SYSCTL_WRITE, + .len = 5, + }; + + w.fd = open(MTU_PATH, O_WRONLY | O_CLOEXEC); + ASSERT_GE(w.fd, 0); + stall_and_remove(_metadata, self, &w); + + /* The table went away while the value was copied in. */ + EXPECT_EQ(w.ret, -1); + EXPECT_EQ(w.err, ENOENT); +} + +TEST_F(proc_sys_slow, getdents) +{ + struct worker w = { + .op = SYSCTL_GETDENTS, + .len = BUF_PAGES * self->psz, + }; + + w.fd = open(CONF_PATH, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + ASSERT_GE(w.fd, 0); + stall_and_remove(_metadata, self, &w); + + /* What was looked up before the removal still arrives, then nothing. */ + EXPECT_GT(w.ret, 0); + EXPECT_EQ(syscall(__NR_getdents64, w.fd, self->buf, self->psz), -1); + EXPECT_EQ(errno, ENOENT); +} + +TEST_HARNESS_MAIN -- 2.53.0