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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=iCTZ0HLl; 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 E64D6608556B; Mon, 2 Nov 2026 15:29:43 +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=iCTZ0HLl Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5ABFE1F00A16; Mon, 2 Nov 2026 15:29:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793633383; bh=AmPg73ZsTa4hWS3OOTC3awBO6zvZml45J7NYZXMvC60=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=iCTZ0HLlYWpNnx3lzizxK8JbxxzlOIlnwN0PzIz6UY8TyRpRaYR72Sb+82Fin1P19 Uq89Sc4uR18wsPrD2qwZSSQbzB+QEEeZcU53jf0zSz5eUKXBjmK4CUBUbNj4BpKSiH g1PfN1jUZKiW6zZ8IInfRG7plrh6BEL3vcjVxlzZSt4sfyNEOX+5HxH2pnDkByJ3iH zi3R2HChW+GDD79p3OJETo/fMAQjBeGqh0tgmAviJY9oTgndZHpyisDmAZcnyucmRF uqCOqicTKRLLVz6FAZmLIgCKbKzLivVkwBn/DT+cTH5rQKoiFnoIZfwVSbluahwRKT gCOgTGaDF9XdA== From: Christian Brauner Date: Mon, 02 Nov 2026 16:07:37 +0100 Subject: [PATCH RFC 27/27] selftests/proc: check that unloading configs doesn't wait for a reader X-Mailing-List: linux-input@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" Content-Transfer-Encoding: 7bit Message-Id: <20261102-work-procfs-fs-v1-27-d09a996317b3@kernel.org> References: <20261102-work-procfs-fs-v1-0-d09a996317b3@kernel.org> In-Reply-To: <20261102-work-procfs-fs-v1-0-d09a996317b3@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-Developer-Signature: v=1; a=openpgp-sha256; l=6916; i=brauner@kernel.org; h=from:subject:message-id; bh=oFCHsIIvTBz60E+Ak0mDBpMOymOH24bqy12BEzEjHtQ=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWS9WG5s9+n5iyVpzR1+S1Yv2LQn7sbvgAOy518pHj6k/ 3vVix0NlzpKWRjEuBhkxRRZHNpNwuWW81RsNsrUgJnDygQyhIGLUwAmcjSIkeHy7QVrGFL87r7Z tTqn+l/utQKPCLlWdkbG2laOBQomEjcZGVq/pl+KCxWY775aK+r5+1f3Oh3yl/oJunu1PFcu1PK OYQQA X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 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) --- 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 +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#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