From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793820730; b=fHseNI3fTm6ZYYyM6FybIXADQ8EnQr6HORCaehy/bcB8LM8Wpnr8HsQyGnf79pFdPvAm IlUKrEMsJhotIAdtiTwv8LFgsVqtPCdQWKCXi1cAfJyqnevKbtUZ268Us//9tWjQ/9cZT gZ8iykglxf8mQZajGAkw9ajw6VSOiFL+AU+4+AaR8FbO3WSG4wd3WG0UmhML9NIv0X/bp QCwwUuESyYRonPfMwiEqLv3i2Nlyzk7BGKLrvpH8m4SKr1l5D5yY8Fz/a3UOHVGJrpU1f zntp2NN0l5XV/60T7T0le8OJMmF49EPGLbY2rk+/Oz+PAbGNPd+dLZzu/MZPb1oC2UA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793820730; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID: In-Reply-To:References:MIME-Version:Content-Type:X-Mailer: X-Developer-Signature:X-Developer-Key:Content-Transfer-Encoding; bh=a8Eii8wlxK/U6i+WN38IP3N9K8zW9fYP0HNd0IGm1W0=; b=is0cJvaY6UIACmxU0+VM0JO3N6UWkmwW85LGFn8UQWkMuXdCGyZA5u/3koQ4/Bj6Y703 6wipr+YzQhtAu5oTEaGJ/ZS7coxRF9iUTcfBapwnblWAvjoCLWdKc+6fMCZcfVHLtMt/q DdukVQOsjDIK6bXbrwtvrqax++p9Zbm67ldqvV4P1DYjrEWFMKfFsWCAaPNqdClnDcqFe a7kNf4woRsct21nJl8mUqGp9uovRDGa5vsdhgRVRX+F2x/oSPqP/GEip7p4mHsHwAOjzh 0rHTo4H4i6rJi6ljTDvLcVCsUew5G9zu+MwHhgMG0LOZzR93N1lz+jMm/qXbt7R9P4A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=iC5qhYuC; 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 6F396606C937; Wed, 4 Nov 2026 19:32:10 +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=iC5qhYuC Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A4421F000C1; Wed, 4 Nov 2026 19:31:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793820730; bh=a8Eii8wlxK/U6i+WN38IP3N9K8zW9fYP0HNd0IGm1W0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=iC5qhYuCRstV+TUqjEu0rWRbTttDUR0KoUFR/Nic2bFwF64VuSt1WDgXx4WbU4Et4 ZNlRYe+G0MHmA1/II6uBNZBPp9Wvcvb5bBVfPJtilV3/K8lP+xGqSdbaN6ECrO9DpW du+eed3fzzQNoHO1No/AbIPvxNJkxVZOJdAGHIz/EgNENL5daivIVmmxtCp9lM8GEv tRA4UQbju+ehP2qFzuoGBNUaSD6Jp1yqYS1bSnF83Bb3YxwerAD9vI0v1JOGv4u38c FoRp/hBAQUDPq4wTOJ5N0tlVFGudcN+g6w+AJBph58Jc+dvlqzJ6WxnPYKNN9XQMYu THb00UuOGzJdA== 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 11/23] selftests/proc: check that a faulting reader doesn't hold up removal Date: Wed, 4 Nov 2026 20:31:56 +0100 Message-ID: <20261104-work-procfs-core-v2-11-76ace653a773@kernel.org> In-Reply-To: <20261104-work-procfs-core-v2-0-76ace653a773@kernel.org> References: <20261104-work-procfs-core-v2-0-76ace653a773@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=5703; i=brauner@kernel.org; h=from:subject:message-id; bh=XyuYjQOPhfqL05zxspI3Sf2ZwFKZLHj6jlvlh6Bj2Lk=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWS9bq97GaEjt/tSvJXDmnqfdIul4otUnkuetLcImZIuI frrsJ9sRykLgxgXg6yYIotDu0m43HKeis1GmRowc1iZQIYwcHEKwETcJjH8D3O/N+uiwGkGvqKb uoYJuYavRK3s+jeLapeqZFQ3hKf7Mfz3X/bwb8DUWRlpKSH5XPOF/65p/KKXLLfq9KTDH5ylnqz hBgA= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 Content-Transfer-Encoding: 8bit Read /proc/net/dev_snmp6/ of a tun device into a buffer whose first page is backed by userfaultfd and remove the device while the reader sleeps in its copy to userspace: - removing the entry doesn't wait for the reader - the reader still gets what was printed before the removal - and the next read fails with -EIO The entry is removed under RTNL, so a regression stalls the 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 + .../selftests/proc/proc-remove-slow-reader.c | 133 +++++++++++++++++++++ 3 files changed, 135 insertions(+) diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore index 3fa89f46b9c7..e2566cc0ae07 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-reader /proc-remove-slow-readlink /read /self diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile index df02699a3587..6a9bdc999f54 100644 --- a/tools/testing/selftests/proc/Makefile +++ b/tools/testing/selftests/proc/Makefile @@ -33,6 +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/proc-remove-slow-reader.c b/tools/testing/selftests/proc/proc-remove-slow-reader.c new file mode 100644 index 000000000000..a201645beca9 --- /dev/null +++ b/tools/testing/selftests/proc/proc-remove-slow-reader.c @@ -0,0 +1,133 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * A read that faults while copying to userspace must not hold up removal of + * the /proc entry. /proc/net/dev_snmp6/ of a tun device is removed 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 SNMP6_PATH "/proc/net/dev_snmp6/" TUN_NAME +#define READ_PAGES 16 +#define TIMEOUT_MS 5000 + +struct reader { + int fd; + char *buf; + size_t len; + ssize_t ret; +}; + +struct closer { + int tun; + int done; +}; + +static void *read_thread(void *arg) +{ + struct reader *r = arg; + + r->ret = read(r->fd, r->buf, r->len); + 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; +} + +TEST(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 ifreq ifr = {}; + struct reader r = {}; + struct closer c = {}; + struct uffd_msg msg; + struct pollfd pfd; + pthread_t rt, ct; + int uffd, done[2]; + char *buf; + + if (unshare(CLONE_NEWNET)) + SKIP(return, "unshare(CLONE_NEWNET): %s", strerror(errno)); + + c.tun = open("/dev/net/tun", O_RDWR | O_CLOEXEC); + if (c.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(c.tun, TUNSETIFF, &ifr), 0); + + r.fd = open(SNMP6_PATH, O_RDONLY | O_CLOEXEC); + if (r.fd < 0) + SKIP(return, SNMP6_PATH ": %s", 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); + + /* 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 its 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); + + /* Closing the device removes the file that is being read. */ + 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("removing " SNMP6_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(ct, NULL), 0); + + /* What was printed before the removal still arrives, then nothing. */ + EXPECT_GT(r.ret, 0); + EXPECT_EQ(read(r.fd, buf, psz), -1); + EXPECT_EQ(errno, EIO); +} + +TEST_HARNESS_MAIN -- 2.53.0