* [PATCH 1/2] selftests/filesystems: add a test for freezing a shared block device
2026-10-12 12:31 [PATCH 0/2] super: convert to a plain hashtable Christian Brauner
@ 2026-10-12 12:31 ` Christian Brauner
2026-10-12 12:31 ` [PATCH 2/2] super: convert to plain hashtable Christian Brauner
1 sibling, 0 replies; 4+ messages in thread
From: Christian Brauner @ 2026-10-12 12:31 UTC (permalink / raw)
To: Jan Kara
Cc: Jens Axboe, Alexander Viro, linux-btrfs, linux-erofs,
linux-fsdevel, Christian Brauner (Amutable)
erofs claims its blob devices with the filesystem type as the holder so
several erofs superblocks can share one. Merge two images from a common
layer and a layer of their own, put the common layer on device-mapper,
mount both and check that:
- a suspend freezes each of them exactly once
- the resume thaws both
- once one of them is unmounted only the other one is frozen
- BLKFLSBUF and ustat() on the shared device work
- mounts that come and go while the device is suspended and resumed
leave nothing frozen behind
mkfs.erofs builds the images, the test is skipped without it.
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
.../selftests/filesystems/freeze/.gitignore | 1 +
.../testing/selftests/filesystems/freeze/Makefile | 2 +-
tools/testing/selftests/filesystems/freeze/config | 1 +
.../filesystems/freeze/shared_bdev_test.c | 479 +++++++++++++++++++++
4 files changed, 482 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/filesystems/freeze/.gitignore b/tools/testing/selftests/filesystems/freeze/.gitignore
index 28f1fe73f19b..2f60f71c3d03 100644
--- a/tools/testing/selftests/filesystems/freeze/.gitignore
+++ b/tools/testing/selftests/filesystems/freeze/.gitignore
@@ -2,3 +2,4 @@
quotactl_test
bdev_freeze_test
bdev_thaw_test
+shared_bdev_test
diff --git a/tools/testing/selftests/filesystems/freeze/Makefile b/tools/testing/selftests/filesystems/freeze/Makefile
index acd246e1b14b..a2b956286b15 100644
--- a/tools/testing/selftests/filesystems/freeze/Makefile
+++ b/tools/testing/selftests/filesystems/freeze/Makefile
@@ -3,6 +3,6 @@ CFLAGS += -Wall -O2 -g $(KHDR_INCLUDES)
LOCAL_HDRS += loop_util.h
TEST_GEN_PROGS := quotactl_test
-TEST_GEN_PROGS += bdev_freeze_test bdev_thaw_test
+TEST_GEN_PROGS += bdev_freeze_test bdev_thaw_test shared_bdev_test
include ../../lib.mk
diff --git a/tools/testing/selftests/filesystems/freeze/config b/tools/testing/selftests/filesystems/freeze/config
index d03720cda9a9..28e568e5d670 100644
--- a/tools/testing/selftests/filesystems/freeze/config
+++ b/tools/testing/selftests/filesystems/freeze/config
@@ -1,6 +1,7 @@
CONFIG_BLK_DEV_DM=y
CONFIG_BLK_DEV_LOOP=y
CONFIG_DEBUG_FS=y
+CONFIG_EROFS_FS=y
CONFIG_EXT4_FS=y
CONFIG_FAIL_MAKE_REQUEST=y
CONFIG_FAULT_INJECTION=y
diff --git a/tools/testing/selftests/filesystems/freeze/shared_bdev_test.c b/tools/testing/selftests/filesystems/freeze/shared_bdev_test.c
new file mode 100644
index 000000000000..0ee352268a97
--- /dev/null
+++ b/tools/testing/selftests/filesystems/freeze/shared_bdev_test.c
@@ -0,0 +1,479 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Freezing a block device that several superblocks share.
+ *
+ * erofs claims its blob devices with the filesystem type as the holder, so
+ * several erofs superblocks can share a blob. Merge two images from a common
+ * layer and a layer of their own, put the common layer on a device-mapper
+ * device and mount both. A suspend of that device has to freeze each of the
+ * two superblocks exactly once and the resume has to thaw both, also while
+ * mounts of one of them come and go. erofs is read-only, so the freezes and
+ * thaws don't write to the suspended device.
+ */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <ftw.h>
+#include <linux/dm-ioctl.h>
+#include <linux/fs.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <sys/sysmacros.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "../../kselftest_harness.h"
+#include "loop_util.h"
+
+#define NR_CHURN 100
+
+enum { M12, M13, L1, L2, L3, NR_IMGS };
+
+static const char *const img_names[NR_IMGS] = { "m12", "m13", "l1", "l2", "l3" };
+
+FIXTURE(shared_bdev) {
+ char dir[64];
+ char a[96];
+ char b[96];
+ char dm[96];
+ char name[32];
+ char src_a[32];
+ char src_b[32];
+ char opts_a[256];
+ char opts_b[256];
+ int loop[NR_IMGS];
+ int fd_a;
+ int fd_b;
+ dev_t dmdev;
+ bool dm_created;
+ bool suspended;
+ bool mounted_a;
+ bool mounted_b;
+};
+
+static int dm_ioctl(unsigned long cmd, const char *name, uint32_t flags, dev_t *dev)
+{
+ struct dm_ioctl dmi = {
+ .version = { DM_VERSION_MAJOR, 0, 0 },
+ .data_size = sizeof(dmi),
+ .data_start = sizeof(dmi),
+ .flags = flags,
+ };
+ int fd, ret = 0;
+
+ strncpy(dmi.name, name, sizeof(dmi.name) - 1);
+ fd = open("/dev/mapper/control", O_RDWR | O_CLOEXEC);
+ if (fd < 0)
+ return -errno;
+ if (ioctl(fd, cmd, &dmi))
+ ret = -errno;
+ else if (dev)
+ *dev = makedev((dmi.dev >> 8) & 0xfff,
+ (dmi.dev & 0xff) | ((dmi.dev >> 12) & 0xfff00));
+ close(fd);
+ return ret;
+}
+
+/* Create @name as a linear mapping of all of @backing and make it live. */
+static int dm_create_linear(const char *name, dev_t backing, uint64_t sectors,
+ dev_t *dev)
+{
+ struct {
+ struct dm_ioctl dmi;
+ struct dm_target_spec spec;
+ char params[64];
+ } __attribute__((aligned(8))) t = {};
+ int fd, ret;
+
+ ret = dm_ioctl(DM_DEV_CREATE, name, 0, NULL);
+ if (ret)
+ return ret;
+
+ t.dmi.version[0] = DM_VERSION_MAJOR;
+ t.dmi.data_size = sizeof(t);
+ t.dmi.data_start = sizeof(t.dmi);
+ t.dmi.target_count = 1;
+ strncpy(t.dmi.name, name, sizeof(t.dmi.name) - 1);
+ t.spec.length = sectors;
+ strcpy(t.spec.target_type, "linear");
+ snprintf(t.params, sizeof(t.params), "%u:%u 0", major(backing), minor(backing));
+
+ fd = open("/dev/mapper/control", O_RDWR | O_CLOEXEC);
+ if (fd >= 0) {
+ ret = ioctl(fd, DM_TABLE_LOAD, &t) ? -errno : 0;
+ close(fd);
+ } else {
+ ret = -errno;
+ }
+ /* Resuming makes the loaded table live. */
+ if (!ret)
+ ret = dm_ioctl(DM_DEV_SUSPEND, name, 0, dev);
+ if (ret)
+ dm_ioctl(DM_DEV_REMOVE, name, 0, NULL);
+ return ret;
+}
+
+static int suspend(FIXTURE_DATA(shared_bdev) *self)
+{
+ int ret = dm_ioctl(DM_DEV_SUSPEND, self->name, DM_SUSPEND_FLAG, NULL);
+
+ if (!ret)
+ self->suspended = true;
+ return ret;
+}
+
+static int resume(FIXTURE_DATA(shared_bdev) *self)
+{
+ int ret = dm_ioctl(DM_DEV_SUSPEND, self->name, 0, NULL);
+
+ if (!ret)
+ self->suspended = false;
+ return ret;
+}
+
+/* Drop one freeze with FITHAW; EINVAL if the superblock isn't frozen. */
+static bool fithaw(int fd)
+{
+ return !ioctl(fd, FITHAW, 0);
+}
+
+static int write_file(const char *path, const char *val)
+{
+ ssize_t len = strlen(val);
+ int fd, ret = 0;
+
+ fd = open(path, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
+ if (fd < 0)
+ return -1;
+ if (write(fd, val, len) != len)
+ ret = -1;
+ close(fd);
+ return ret;
+}
+
+static int check_file(const char *path, const char *val)
+{
+ char buf[32] = {};
+ int fd;
+
+ fd = open(path, O_RDONLY | O_CLOEXEC);
+ if (fd < 0)
+ return -1;
+ if (read(fd, buf, sizeof(buf) - 1) < 0)
+ buf[0] = '\0';
+ close(fd);
+ return strcmp(buf, val) ? -1 : 0;
+}
+
+static int rm_one(const char *path, const struct stat *st, int type, struct FTW *ftw)
+{
+ return remove(path);
+}
+
+static int mount_b(FIXTURE_DATA(shared_bdev) *self)
+{
+ int ret = mount(self->src_b, self->b, "erofs", MS_RDONLY, self->opts_b);
+
+ if (!ret)
+ self->mounted_b = true;
+ return ret;
+}
+
+static void shared_bdev_cleanup(FIXTURE_DATA(shared_bdev) *self)
+{
+ if (self->suspended)
+ resume(self);
+ if (self->fd_a >= 0)
+ close(self->fd_a);
+ if (self->fd_b >= 0)
+ close(self->fd_b);
+ if (self->mounted_a)
+ umount2(self->a, MNT_DETACH);
+ umount2(self->b, MNT_DETACH);
+ if (self->dm_created)
+ dm_ioctl(DM_DEV_REMOVE, self->name, 0, NULL);
+ for (int i = 0; i < NR_IMGS; i++) {
+ if (self->loop[i] >= 0)
+ loop_clear(self->loop[i]);
+ }
+ nftw(self->dir, rm_one, 16, FTW_DEPTH | FTW_PHYS);
+}
+
+/* Two layers of their own, a common one, and two images merged from them. */
+static int make_images(const char *dir)
+{
+ static const char *const files[][2] = {
+ { "src-l1/d1/f1", "one\n" },
+ { "src-l2/f2", "two\n" },
+ { "src-l3/f3", "three\n" },
+ };
+ char path[160], cmd[512];
+
+ for (int i = 0; i < 3; i++) {
+ snprintf(path, sizeof(path), "%s/src-l%d", dir, i + 1);
+ if (mkdir(path, 0755))
+ return -1;
+ }
+ snprintf(path, sizeof(path), "%s/src-l1/d1", dir);
+ if (mkdir(path, 0755))
+ return -1;
+ for (int i = 0; i < 3; i++) {
+ snprintf(path, sizeof(path), "%s/%s", dir, files[i][0]);
+ if (write_file(path, files[i][1]))
+ return -1;
+ }
+
+ /* Chunk-based layers can be referenced by the merged images. */
+ snprintf(cmd, sizeof(cmd),
+ "cd %s && (for l in l1 l2 l3; do "
+ "mkfs.erofs --chunksize=4096 -Enoinline_data $l src-$l || exit 1; done && "
+ "mkfs.erofs m12 l1 l2 && mkfs.erofs m13 l1 l3) >/dev/null 2>&1", dir);
+ return system(cmd) ? -1 : 0;
+}
+
+FIXTURE_SETUP(shared_bdev)
+{
+ struct stat img, lst, st;
+ char path[160], dev[32];
+ int fd;
+
+ for (int i = 0; i < NR_IMGS; i++)
+ self->loop[i] = -1;
+ self->fd_a = -1;
+ self->fd_b = -1;
+ self->dm_created = false;
+ self->suspended = false;
+ self->mounted_a = false;
+ self->mounted_b = false;
+
+ if (geteuid() != 0)
+ SKIP(return, "test requires CAP_SYS_ADMIN");
+ if (access("/dev/loop-control", R_OK | W_OK))
+ SKIP(return, "test requires loop devices");
+ if (access("/dev/mapper/control", R_OK | W_OK))
+ SKIP(return, "test requires device-mapper");
+
+ ASSERT_EQ(unshare(CLONE_NEWNS), 0);
+ ASSERT_EQ(mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, NULL), 0);
+
+ snprintf(self->dir, sizeof(self->dir), "/tmp/shared_bdev.XXXXXX");
+ ASSERT_NE(mkdtemp(self->dir), NULL);
+ snprintf(self->a, sizeof(self->a), "%s/a", self->dir);
+ snprintf(self->b, sizeof(self->b), "%s/b", self->dir);
+ snprintf(self->name, sizeof(self->name), "shared_bdev_%d", getpid());
+ /* The harness doesn't run the teardown when the setup fails. */
+ ASSERT_EQ(mkdir(self->a, 0700), 0)
+ shared_bdev_cleanup(self);
+ ASSERT_EQ(mkdir(self->b, 0700), 0)
+ shared_bdev_cleanup(self);
+
+ if (make_images(self->dir)) {
+ shared_bdev_cleanup(self);
+ SKIP(return, "mkfs.erofs failed, is missing or can't merge images");
+ }
+
+ for (int i = 0; i < NR_IMGS; i++) {
+ snprintf(path, sizeof(path), "%s/%s", self->dir, img_names[i]);
+ fd = open(path, O_RDWR | O_CLOEXEC);
+ ASSERT_GE(fd, 0)
+ shared_bdev_cleanup(self);
+ self->loop[i] = loop_bind(fd);
+ if (i == L1) {
+ ASSERT_EQ(fstat(fd, &img), 0)
+ shared_bdev_cleanup(self);
+ }
+ close(fd);
+ ASSERT_GE(self->loop[i], 0)
+ shared_bdev_cleanup(self);
+ }
+
+ /* The common layer goes on a device-mapper device. */
+ snprintf(dev, sizeof(dev), "/dev/loop%d", self->loop[L1]);
+ ASSERT_EQ(stat(dev, &lst), 0)
+ shared_bdev_cleanup(self);
+ ASSERT_EQ(dm_create_linear(self->name, lst.st_rdev, img.st_size >> 9, &self->dmdev), 0)
+ shared_bdev_cleanup(self);
+ self->dm_created = true;
+ snprintf(self->dm, sizeof(self->dm), "/dev/dm-%u", minor(self->dmdev));
+ if (stat(self->dm, &st) || st.st_rdev != self->dmdev) {
+ snprintf(self->dm, sizeof(self->dm), "%s/dm", self->dir);
+ ASSERT_EQ(mknod(self->dm, S_IFBLK | 0600, self->dmdev), 0)
+ shared_bdev_cleanup(self);
+ }
+
+ snprintf(self->src_a, sizeof(self->src_a), "/dev/loop%d", self->loop[M12]);
+ snprintf(self->src_b, sizeof(self->src_b), "/dev/loop%d", self->loop[M13]);
+ snprintf(self->opts_a, sizeof(self->opts_a), "device=%s,device=/dev/loop%d",
+ self->dm, self->loop[L2]);
+ snprintf(self->opts_b, sizeof(self->opts_b), "device=%s,device=/dev/loop%d",
+ self->dm, self->loop[L3]);
+
+ if (mount(self->src_a, self->a, "erofs", MS_RDONLY, self->opts_a)) {
+ if (errno == ENODEV) {
+ shared_bdev_cleanup(self);
+ SKIP(return, "kernel lacks erofs");
+ }
+ ASSERT_EQ(errno, 0)
+ shared_bdev_cleanup(self);
+ }
+ self->mounted_a = true;
+ ASSERT_EQ(mount_b(self), 0)
+ shared_bdev_cleanup(self);
+
+ /* Both read through the shared blob. */
+ snprintf(path, sizeof(path), "%s/d1/f1", self->a);
+ ASSERT_EQ(check_file(path, "one\n"), 0)
+ shared_bdev_cleanup(self);
+ snprintf(path, sizeof(path), "%s/f2", self->a);
+ ASSERT_EQ(check_file(path, "two\n"), 0)
+ shared_bdev_cleanup(self);
+ snprintf(path, sizeof(path), "%s/d1/f1", self->b);
+ ASSERT_EQ(check_file(path, "one\n"), 0)
+ shared_bdev_cleanup(self);
+ snprintf(path, sizeof(path), "%s/f3", self->b);
+ ASSERT_EQ(check_file(path, "three\n"), 0)
+ shared_bdev_cleanup(self);
+
+ self->fd_a = open(self->a, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+ ASSERT_GE(self->fd_a, 0)
+ shared_bdev_cleanup(self);
+ self->fd_b = open(self->b, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+ ASSERT_GE(self->fd_b, 0)
+ shared_bdev_cleanup(self);
+}
+
+FIXTURE_TEARDOWN(shared_bdev)
+{
+ shared_bdev_cleanup(self);
+}
+
+TEST_F(shared_bdev, suspend_freezes_each_once)
+{
+ ASSERT_EQ(suspend(self), 0);
+
+ /* One FITHAW drops each freeze, a second one finds nothing frozen. */
+ ASSERT_TRUE(fithaw(self->fd_a));
+ ASSERT_FALSE(fithaw(self->fd_a));
+ ASSERT_EQ(errno, EINVAL);
+ ASSERT_TRUE(fithaw(self->fd_b));
+ ASSERT_FALSE(fithaw(self->fd_b));
+ ASSERT_EQ(errno, EINVAL);
+
+ /* The resume finds nothing left to thaw and still thaws the device. */
+ ASSERT_EQ(resume(self), 0);
+ ASSERT_EQ(suspend(self), 0);
+ ASSERT_EQ(resume(self), 0);
+}
+
+TEST_F(shared_bdev, resume_thaws_all)
+{
+ ASSERT_EQ(suspend(self), 0);
+ ASSERT_EQ(resume(self), 0);
+
+ ASSERT_FALSE(fithaw(self->fd_a));
+ ASSERT_EQ(errno, EINVAL);
+ ASSERT_FALSE(fithaw(self->fd_b));
+ ASSERT_EQ(errno, EINVAL);
+}
+
+TEST_F(shared_bdev, unmounted_sharer)
+{
+ close(self->fd_b);
+ self->fd_b = -1;
+ ASSERT_EQ(umount2(self->b, 0), 0);
+ self->mounted_b = false;
+
+ /* Only the remaining superblock is frozen, once. */
+ ASSERT_EQ(suspend(self), 0);
+ ASSERT_TRUE(fithaw(self->fd_a));
+ ASSERT_FALSE(fithaw(self->fd_a));
+ ASSERT_EQ(errno, EINVAL);
+ ASSERT_EQ(resume(self), 0);
+
+ /* The blob can be claimed again. */
+ ASSERT_EQ(mount_b(self), 0);
+}
+
+TEST_F(shared_bdev, flushbuf)
+{
+ int fd = open(self->dm, O_RDONLY | O_CLOEXEC);
+
+ ASSERT_GE(fd, 0);
+ /* BLKFLSBUF syncs every superblock that uses the device. */
+ ASSERT_EQ(ioctl(fd, BLKFLSBUF, 0), 0);
+ close(fd);
+}
+
+#ifdef __NR_ustat
+/* struct ustat is not exported through UAPI, mirror include/linux/types.h. */
+struct ustat_buf {
+ int f_tfree;
+ unsigned long f_tinode;
+ char f_fname[6];
+ char f_fpack[6];
+ char pad[64];
+};
+
+TEST_F(shared_bdev, ustat)
+{
+ struct ustat_buf buf;
+
+ /* ustat() stops at the first superblock it can lock... */
+ ASSERT_EQ(syscall(__NR_ustat, (unsigned int)self->dmdev, &buf), 0);
+
+ /* ...and the walks after it still reach both. */
+ ASSERT_EQ(suspend(self), 0);
+ ASSERT_TRUE(fithaw(self->fd_a));
+ ASSERT_TRUE(fithaw(self->fd_b));
+ ASSERT_EQ(resume(self), 0);
+}
+#endif
+
+TEST_F(shared_bdev, churn)
+{
+ int status;
+ pid_t pid;
+
+ close(self->fd_b);
+ self->fd_b = -1;
+ ASSERT_EQ(umount2(self->b, 0), 0);
+ self->mounted_b = false;
+
+ pid = fork();
+ ASSERT_GE(pid, 0);
+ if (pid == 0) {
+ /* A mount while the device is frozen is refused with EBUSY. */
+ for (int i = 0; i < NR_CHURN; i++) {
+ if (!mount(self->src_b, self->b, "erofs", MS_RDONLY, self->opts_b)) {
+ if (umount2(self->b, 0))
+ _exit(1);
+ } else if (errno != EBUSY) {
+ _exit(2);
+ }
+ }
+ _exit(0);
+ }
+
+ for (int i = 0; i < NR_CHURN; i++) {
+ ASSERT_EQ(suspend(self), 0);
+ ASSERT_EQ(resume(self), 0);
+ }
+ ASSERT_EQ(waitpid(pid, &status, 0), pid);
+ ASSERT_TRUE(WIFEXITED(status));
+ ASSERT_EQ(WEXITSTATUS(status), 0);
+
+ /* Nothing is left frozen and the blob can be claimed again. */
+ ASSERT_FALSE(fithaw(self->fd_a));
+ ASSERT_EQ(errno, EINVAL);
+ ASSERT_EQ(mount_b(self), 0);
+}
+
+TEST_HARNESS_MAIN
--
2.53.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH 2/2] super: convert to plain hashtable
2026-10-12 12:31 [PATCH 0/2] super: convert to a plain hashtable Christian Brauner
2026-10-12 12:31 ` [PATCH 1/2] selftests/filesystems: add a test for freezing a shared block device Christian Brauner
@ 2026-10-12 12:31 ` Christian Brauner
2026-10-12 16:16 ` Jan Kara
1 sibling, 1 reply; 4+ messages in thread
From: Christian Brauner @ 2026-10-12 12:31 UTC (permalink / raw)
To: Jan Kara
Cc: Jens Axboe, Alexander Viro, linux-btrfs, linux-erofs,
linux-fsdevel, Christian Brauner (Amutable)
Convert the rhltable to a plain hashtable under a spinlock. The walks
keep their place with a cursor entry in the chain. A claim is unhashed
the moment it's dropped and a walk that finds a superblock that isn't
born yet waits for it to be born or to die and looks again. Since
hashing can't fail anymore the entry for the superblock's own s_dev is
embedded in struct super_block and the preallocation in alloc_super()
goes away. This all simplifies things quite a lot.
It also fixes a btrfs bug where fs_bdev_freeze() ended up freezing a
btrfs filesystem through a stale member that open_ctree() had already
released while the freeze was waiting for SB_BORN. The resume doesn't
find a holder for that device anymore so the filesystem stays frozen
for good.
The walks return superblocks instead of table entries now and
user_get_super() hands out the passive reference the walk took.
Reproducer, a three device btrfs with a stale copy of a removed member.
dm-delay under the remaining members stretches the window between
btrfs_open_devices() and btrfs_free_extra_devids():
truncate -s 1G a1 a2 b
A1=$(losetup -f --show a1); A2=$(losetup -f --show a2); B=$(losetup -f --show b)
mkfs.btrfs -f -d single -m single $A1 $A2 $B
cp b b.old
mount $A1 /mnt && btrfs device remove 3 /mnt && umount /mnt
OLD=$(losetup -f --show b.old)
dmsetup create d1 --table "0 $(blockdev --getsz $A1) delay $A1 0 200"
dmsetup create d2 --table "0 $(blockdev --getsz $A2) delay $A2 0 200"
dmsetup create old --table "0 $(blockdev --getsz $OLD) linear $OLD 0"
mount -o device=/dev/mapper/d2,device=/dev/mapper/old /dev/mapper/d1 /mnt &
sleep 1; dmsetup suspend old; wait
dmsetup resume old
touch /mnt/foo # hangs until fsfreeze -u /mnt
That left btrfs frozen in 5 of 5 rounds with the same tables issued
through raw dm ioctls. The -o degraded variant needs the mount held
between the insertion and the bd_fsfreeze_count check in
fs_bdev_register() with a kprobe.
Fixes: cdb5146f8d5f ("fs: look up superblocks via the device table in fs_holder_ops")
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
block/bdev.c | 2 +-
fs/internal.h | 1 -
fs/namespace.c | 2 -
fs/super.c | 332 +++++++++++++++++------------------------
include/linux/fs/super_types.h | 11 +-
5 files changed, 145 insertions(+), 203 deletions(-)
diff --git a/block/bdev.c b/block/bdev.c
index cd8323083740..5e996f86d2ff 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1283,7 +1283,7 @@ int lookup_bdev(const char *pathname, dev_t *dev)
* registers major 0. Fake block device inodes (e.g. fuse with
* rootmode=S_IFBLK) can expose i_rdev == 0, and letting that
* propagate would confuse superblock lookup and trigger warnings
- * in the device-to-superblock table (super_dev_register).
+ * in the device-to-superblock table (sget_fc).
*/
error = -ENODEV;
if (!inode->i_rdev)
diff --git a/fs/internal.h b/fs/internal.h
index c658c8a5ebd5..67aa0444351b 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -137,7 +137,6 @@ extern int reconfigure_super(struct fs_context *);
extern bool super_trylock_shared(struct super_block *sb);
struct super_block *user_get_super(dev_t, bool excl);
void put_super(struct super_block *sb);
-void __init super_dev_init(void);
extern bool mount_capable(struct fs_context *);
/*
diff --git a/fs/namespace.c b/fs/namespace.c
index 3ed3766f3a18..4c3816256ae2 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -6470,8 +6470,6 @@ void __init mnt_init(void)
HASH_ZERO,
&mp_hash_shift, &mp_hash_mask, 0, 0);
- super_dev_init();
-
kernfs_init();
err = sysfs_init();
diff --git a/fs/super.c b/fs/super.c
index 657958a1d135..eb5f355c88d7 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -25,7 +25,7 @@
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/memcontrol.h>
-#include <linux/rhashtable.h>
+#include <linux/hashtable.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/writeback.h> /* for the emergency remount stuff */
@@ -274,8 +274,6 @@ static unsigned long super_cache_count(struct shrinker *shrink,
return total_objects;
}
-static struct super_dev *super_dev_alloc(dev_t dev, struct super_block *sb);
-
static void destroy_super_work(struct work_struct *work)
{
struct super_block *s = container_of(work, struct super_block,
@@ -283,8 +281,6 @@ static void destroy_super_work(struct work_struct *work)
fsnotify_sb_free(s);
security_sb_free(s);
put_user_ns(s->s_user_ns);
- /* Only an unregistered entry is still owned by the superblock. */
- kfree(s->s_super_dev);
kfree(s->s_subtype);
for (int i = 0; i < SB_FREEZE_LEVELS; i++)
percpu_free_rwsem(&s->s_writers.rw_sem[i]);
@@ -398,9 +394,6 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
goto fail;
if (list_lru_init_memcg(&s->s_inode_lru, s->s_shrink))
goto fail;
- s->s_super_dev = super_dev_alloc(0, s);
- if (!s->s_super_dev)
- goto fail;
s->s_min_writeback_pages = MIN_WRITEBACK_PAGES;
return s;
@@ -435,110 +428,92 @@ void put_super(struct super_block *s)
}
}
-struct super_dev {
- dev_t sd_dev;
- struct super_block *sd_sb;
- refcount_t sd_ref;
- struct rhlist_head sd_node;
- struct rcu_head sd_rcu;
-};
-
-static struct rhltable super_dev_table;
-static const struct rhashtable_params super_dev_params = {
- .key_len = sizeof(dev_t),
- .key_offset = offsetof(struct super_dev, sd_dev),
- .head_offset = offsetof(struct super_dev, sd_node),
-};
-
-static struct super_dev *super_dev_alloc(dev_t dev, struct super_block *sb)
-{
- struct super_dev *fsd;
-
- fsd = kzalloc_obj(*fsd);
- if (!fsd)
- return NULL;
- fsd->sd_dev = dev;
- fsd->sd_sb = sb;
- refcount_set(&fsd->sd_ref, 1);
- return fsd;
-}
+/*
+ * Superblocks hashed by the devices they claim: s_dev from sget_fc() to
+ * kill_super_notify() and every block device opened through
+ * fs_bdev_file_open_by_{dev,path}(). Walks keep their place with a cursor, an
+ * entry without a superblock.
+ */
+#define SUPER_DEV_HASH_BITS 8
+static DEFINE_HASHTABLE(super_dev_hash, SUPER_DEV_HASH_BITS);
+static DEFINE_SPINLOCK(super_dev_lock);
-static void super_dev_put(struct super_dev *fsd)
+static void super_dev_add(struct super_dev *sd, struct super_block *sb, dev_t dev)
{
- /* Unlink only once unpinned, so a cursor never resumes from a removed node. */
- if (fsd && refcount_dec_and_test(&fsd->sd_ref)) {
- rhltable_remove(&super_dev_table, &fsd->sd_node, super_dev_params);
- put_super(fsd->sd_sb);
- kfree_rcu(fsd, sd_rcu);
- }
-}
+ lockdep_assert_held(&super_dev_lock);
-void __init super_dev_init(void)
-{
- if (rhltable_init(&super_dev_table, &super_dev_params))
- panic("VFS: Cannot initialise super_dev_table\n");
+ sd->sd_sb = sb;
+ sd->sd_dev = dev;
+ sd->sd_claims = 1;
+ refcount_inc(&sb->s_passive);
+ hash_add(super_dev_hash, &sd->sd_hash, dev);
}
-static int super_dev_insert(struct super_dev *fsd)
+/* Drop a claim, the last one unhashes the entry. */
+static void super_dev_put(struct super_dev *sd)
{
- int err;
+ struct super_block *sb = sd->sd_sb;
- err = rhltable_insert(&super_dev_table, &fsd->sd_node, super_dev_params);
- if (!err)
- refcount_inc(&fsd->sd_sb->s_passive);
- return err;
+ scoped_guard(spinlock, &super_dev_lock) {
+ if (--sd->sd_claims)
+ return;
+ hash_del(&sd->sd_hash);
+ }
+ if (sd != &sb->s_super_dev)
+ kfree(sd);
+ put_super(sb);
}
-/* Register @sb under @sb->s_dev as the final fallible act of a set callback. */
-static int super_dev_register(struct super_block *sb)
+/*
+ * Return the superblock of the next claim behind @cursor with a passive
+ * reference and put @prev. The mount of a superblock that isn't born yet may
+ * still drop its claim, so wait for it to be born or to die and look again.
+ */
+static struct super_block *super_dev_next(struct super_dev *cursor,
+ struct super_block *prev)
{
- struct super_dev *fsd = sb->s_super_dev;
- int err;
-
- lockdep_assert_held(&sb_lock);
- VFS_WARN_ON_ONCE(!sb->s_dev);
- VFS_WARN_ON_ONCE(!fsd || fsd->sd_dev);
+ struct super_block *sb;
+ struct super_dev *sd;
- fsd->sd_dev = sb->s_dev;
- err = super_dev_insert(fsd);
- if (err)
- fsd->sd_dev = 0;
- return err;
-}
+ if (prev)
+ put_super(prev);
-static struct super_dev *super_dev_get(struct rhlist_head *pos)
-{
- struct super_dev *sb_dev;
+ for (;;) {
+ scoped_guard(spinlock, &super_dev_lock) {
+ if (!hash_hashed(&cursor->sd_hash))
+ hash_add(super_dev_hash, &cursor->sd_hash, cursor->sd_dev);
+ sd = cursor;
+ hlist_for_each_entry_continue(sd, sd_hash) {
+ if (sd->sd_sb && sd->sd_dev == cursor->sd_dev)
+ break;
+ }
+ if (!sd) {
+ hash_del(&cursor->sd_hash);
+ return NULL;
+ }
- for (; pos; pos = rcu_dereference_all(pos->next)) {
- sb_dev = container_of(pos, struct super_dev, sd_node);
- if (refcount_inc_not_zero(&sb_dev->sd_ref))
- return sb_dev;
+ sb = sd->sd_sb;
+ refcount_inc(&sb->s_passive);
+ if (super_flags(sb, SB_BORN | SB_DYING)) {
+ hash_del(&cursor->sd_hash);
+ hlist_add_behind(&cursor->sd_hash, &sd->sd_hash);
+ return sb;
+ }
+ }
+ wait_var_event(&sb->s_flags, super_flags(sb, SB_BORN | SB_DYING));
+ put_super(sb);
}
- return NULL;
}
-static struct super_dev *super_dev_first(dev_t dev)
+/* Unhash the cursor of a walk that stops early. */
+static void super_dev_walk_end(struct super_dev *cursor)
{
- struct super_dev *sb_dev;
-
- rcu_read_lock();
- sb_dev = super_dev_get(rhltable_lookup(&super_dev_table, &dev, super_dev_params));
- rcu_read_unlock();
- return sb_dev;
+ guard(spinlock)(&super_dev_lock);
+ hash_del(&cursor->sd_hash);
}
-static struct super_dev *super_dev_next(struct super_dev *prev)
-{
- struct super_dev *sb_dev;
-
- rcu_read_lock();
- sb_dev = super_dev_get(rcu_dereference_all(prev->sd_node.next));
- rcu_read_unlock();
-
- super_dev_put(prev);
- return sb_dev;
-}
+#define for_each_dev_super(sb, cursor) \
+ for (sb = super_dev_next(cursor, NULL); sb; sb = super_dev_next(cursor, sb))
static void kill_super_notify(struct super_block *sb)
{
@@ -548,11 +523,8 @@ static void kill_super_notify(struct super_block *sb)
if (sb->s_flags & SB_DEAD)
return;
- /* Drop sget_fc()'s claim; a never-registered entry stays with the sb. */
- if (sb->s_super_dev->sd_dev) {
- super_dev_put(sb->s_super_dev);
- sb->s_super_dev = NULL;
- }
+ /* Drop sget_fc()'s claim on s_dev. */
+ super_dev_put(&sb->s_super_dev);
/*
* Let concurrent mounts know that this thing is really dead.
@@ -880,13 +852,12 @@ struct super_block *sget_fc(struct fs_context *fc,
s->s_fs_info = fc->s_fs_info;
err = set(s, fc);
if (err) {
- VFS_WARN_ON_ONCE(s->s_super_dev->sd_dev);
s->s_fs_info = NULL;
spin_unlock(&sb_lock);
destroy_unused_super(s);
return ERR_PTR(err);
}
- VFS_WARN_ON_ONCE(!s->s_super_dev->sd_dev);
+ VFS_WARN_ON_ONCE(!s->s_dev);
fc->s_fs_info = NULL;
s->s_type = fc->fs_type;
s->s_iflags |= fc->s_iflags;
@@ -899,6 +870,8 @@ struct super_block *sget_fc(struct fs_context *fc,
list_add_tail(&s->s_list, &super_blocks);
hlist_add_head(&s->s_instances, &s->s_type->fs_supers);
spin_unlock(&sb_lock);
+ scoped_guard(spinlock, &super_dev_lock)
+ super_dev_add(&s->s_super_dev, s, s->s_dev);
get_filesystem(s->s_type);
shrinker_register(s->s_shrink);
return s;
@@ -1040,18 +1013,14 @@ EXPORT_SYMBOL(iterate_supers_type);
struct super_block *user_get_super(dev_t dev, bool excl)
{
- struct super_dev *sb_dev;
-
- for (sb_dev = super_dev_first(dev); sb_dev; sb_dev = super_dev_next(sb_dev)) {
- struct super_block *sb = sb_dev->sd_sb;
-
- if (!super_lock(sb, excl))
- continue;
+ struct super_dev cursor = { .sd_dev = dev };
+ struct super_block *sb;
- /* The pinned entry holds a passive reference, take our own. */
- refcount_inc(&sb->s_passive);
- super_dev_put(sb_dev);
- return sb;
+ for_each_dev_super(sb, &cursor) {
+ if (super_lock(sb, excl)) {
+ super_dev_walk_end(&cursor);
+ return sb;
+ }
}
return NULL;
}
@@ -1353,16 +1322,7 @@ EXPORT_SYMBOL(free_anon_bdev);
int set_anon_super(struct super_block *s, void *data)
{
- int error;
-
- error = get_anon_bdev(&s->s_dev);
- if (error)
- return error;
-
- error = super_dev_register(s);
- if (error)
- free_anon_bdev(s->s_dev);
- return error;
+ return get_anon_bdev(&s->s_dev);
}
EXPORT_SYMBOL(set_anon_super);
@@ -1448,7 +1408,7 @@ EXPORT_SYMBOL(get_tree_keyed);
static int set_bdev_super(struct super_block *s, void *data)
{
s->s_dev = *(dev_t *)data;
- return super_dev_register(s);
+ return 0;
}
static int super_s_dev_set(struct super_block *s, struct fs_context *fc)
@@ -1527,14 +1487,12 @@ static int fs_super_thaw(struct super_block *sb)
static void fs_bdev_mark_dead(struct block_device *bdev, bool surprise)
{
- struct super_dev *sb_dev;
- dev_t dev = bdev->bd_dev;
+ struct super_dev cursor = { .sd_dev = bdev->bd_dev };
+ struct super_block *sb;
mutex_unlock(&bdev->bd_holder_lock);
- for (sb_dev = super_dev_first(dev); sb_dev; sb_dev = super_dev_next(sb_dev)) {
- struct super_block *sb = sb_dev->sd_sb;
-
+ for_each_dev_super(sb, &cursor) {
if (!super_lock_shared(sb))
continue;
if (sb->s_root && (sb->s_flags & SB_ACTIVE)) {
@@ -1554,14 +1512,12 @@ static void fs_bdev_mark_dead(struct block_device *bdev, bool surprise)
static void fs_bdev_sync(struct block_device *bdev)
{
- struct super_dev *sb_dev;
- dev_t dev = bdev->bd_dev;
+ struct super_dev cursor = { .sd_dev = bdev->bd_dev };
+ struct super_block *sb;
mutex_unlock(&bdev->bd_holder_lock);
- for (sb_dev = super_dev_first(dev); sb_dev; sb_dev = super_dev_next(sb_dev)) {
- struct super_block *sb = sb_dev->sd_sb;
-
+ for_each_dev_super(sb, &cursor) {
if (!super_lock_shared(sb))
continue;
if (sb->s_root && (sb->s_flags & SB_ACTIVE))
@@ -1585,8 +1541,8 @@ static void fs_bdev_sync(struct block_device *bdev)
*/
static int fs_bdev_freeze(struct block_device *bdev)
{
- dev_t dev = bdev->bd_dev;
- struct super_dev *sb_dev;
+ struct super_dev cursor = { .sd_dev = bdev->bd_dev };
+ struct super_block *sb;
unsigned int count = 0;
int error = 0, err;
@@ -1594,13 +1550,13 @@ static int fs_bdev_freeze(struct block_device *bdev)
mutex_unlock(&bdev->bd_holder_lock);
- for (sb_dev = super_dev_first(dev); sb_dev; sb_dev = super_dev_next(sb_dev)) {
- if (!get_active_super(sb_dev->sd_sb))
+ for_each_dev_super(sb, &cursor) {
+ if (!get_active_super(sb))
continue;
- err = fs_super_freeze(sb_dev->sd_sb);
+ err = fs_super_freeze(sb);
if (err && !error)
error = err;
- deactivate_super(sb_dev->sd_sb);
+ deactivate_super(sb);
count++;
}
@@ -1640,8 +1596,8 @@ static int fs_bdev_freeze(struct block_device *bdev)
*/
static int fs_bdev_thaw(struct block_device *bdev)
{
- dev_t dev = bdev->bd_dev;
- struct super_dev *sb_dev;
+ struct super_dev cursor = { .sd_dev = bdev->bd_dev };
+ struct super_block *sb;
unsigned int count = 0;
int error = 0, err;
@@ -1649,13 +1605,13 @@ static int fs_bdev_thaw(struct block_device *bdev)
mutex_unlock(&bdev->bd_holder_lock);
- for (sb_dev = super_dev_first(dev); sb_dev; sb_dev = super_dev_next(sb_dev)) {
- if (!get_active_super(sb_dev->sd_sb))
+ for_each_dev_super(sb, &cursor) {
+ if (!get_active_super(sb))
continue;
- err = fs_super_thaw(sb_dev->sd_sb);
+ err = fs_super_thaw(sb);
if (err && !error)
error = err;
- deactivate_super(sb_dev->sd_sb);
+ deactivate_super(sb);
count++;
}
@@ -1672,55 +1628,39 @@ static const struct blk_holder_ops fs_holder_ops = {
.thaw = fs_bdev_thaw,
};
-static struct super_dev *super_dev_lookup(dev_t dev, struct super_block *sb)
+static struct super_dev *super_dev_find(dev_t dev, const struct super_block *sb)
{
- struct super_dev *it;
- struct rhlist_head *list, *pos;
+ struct super_dev *sd;
- RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "suspicious super_dev_lookup() usage");
- VFS_WARN_ON_ONCE(!dev);
- VFS_WARN_ON_ONCE(!sb);
+ lockdep_assert_held(&super_dev_lock);
- list = rhltable_lookup(&super_dev_table, &dev, super_dev_params);
- rhl_for_each_entry_rcu(it, pos, list, sd_node) {
- if (it->sd_sb == sb)
- return it;
+ hash_for_each_possible(super_dev_hash, sd, sd_hash, dev) {
+ if (sd->sd_dev == dev && sd->sd_sb == sb)
+ return sd;
}
-
return NULL;
}
-static int fs_bdev_register(struct file *bdev_file, struct super_block *sb)
+static int fs_bdev_register(struct block_device *bdev, struct super_block *sb)
{
- struct super_dev *sb_dev __free(kfree) = NULL;
- dev_t dev = file_bdev(bdev_file)->bd_dev;
- int err;
-
- scoped_guard(rcu) {
- sb_dev = super_dev_lookup(dev, sb);
- if (sb_dev && refcount_inc_not_zero(&sb_dev->sd_ref)) {
- retain_and_null_ptr(sb_dev);
- return 0;
- }
- }
-
- sb_dev = super_dev_alloc(dev, sb);
- if (!sb_dev)
- return -ENOMEM;
+ struct super_dev *new __free(kfree) = NULL;
+ struct super_dev *sd;
- err = super_dev_insert(sb_dev);
- if (err)
- return err;
+ new = kzalloc_obj(*new);
- /* Publish the entry before reading the count; pairs with bdev_freeze(). */
- smp_mb();
- if (atomic_read(&file_bdev(bdev_file)->bd_fsfreeze_count) > 0) {
- err = -EBUSY;
- super_dev_put(sb_dev);
+ guard(spinlock)(&super_dev_lock);
+ sd = super_dev_find(bdev->bd_dev, sb);
+ if (sd) {
+ sd->sd_claims++;
+ return 0;
}
-
- retain_and_null_ptr(sb_dev);
- return err;
+ /* bdev_freeze() raises the count before its walk takes the lock. */
+ if (atomic_read(&bdev->bd_fsfreeze_count) > 0)
+ return -EBUSY;
+ if (!new)
+ return -ENOMEM;
+ super_dev_add(no_free_ptr(new), sb, bdev->bd_dev);
+ return 0;
}
/**
@@ -1747,7 +1687,7 @@ struct file *fs_bdev_file_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
if (IS_ERR(bdev_file))
return bdev_file;
- err = fs_bdev_register(bdev_file, sb);
+ err = fs_bdev_register(file_bdev(bdev_file), sb);
if (err) {
bdev_fput(bdev_file);
return ERR_PTR(err);
@@ -1781,7 +1721,7 @@ struct file *fs_bdev_file_open_by_path(const char *path, blk_mode_t mode,
if (IS_ERR(bdev_file))
return bdev_file;
- err = fs_bdev_register(bdev_file, sb);
+ err = fs_bdev_register(file_bdev(bdev_file), sb);
if (err) {
bdev_fput(bdev_file);
return ERR_PTR(err);
@@ -1796,21 +1736,20 @@ EXPORT_SYMBOL_GPL(fs_bdev_file_open_by_path);
* @sb: superblock the device was claimed for
*
* The inverse of fs_bdev_register(): drop one claim on the {dev, @sb} entry
- * (the last claim unregisters it; a pinning cursor defers the actual unlink)
- * without closing the device. A caller that must act on the still-open device
- * between unregistering and closing - e.g. re-allow freezing one denied for a
- * membership change - pairs this with bdev_fput(). fs_bdev_file_release() is
- * the common unregister-and-close.
+ * (the last claim unregisters it) without closing the device. A caller that
+ * must act on the still-open device between unregistering and closing - e.g.
+ * re-allow freezing one denied for a membership change - pairs this with
+ * bdev_fput(). fs_bdev_file_release() is the common unregister-and-close.
*/
void fs_bdev_unregister(struct file *bdev_file, struct super_block *sb)
{
- dev_t dev = file_bdev(bdev_file)->bd_dev;
- struct super_dev *sb_dev;
+ struct super_dev *sd;
- rcu_read_lock();
- sb_dev = super_dev_lookup(dev, sb);
- rcu_read_unlock();
- super_dev_put(sb_dev);
+ /* The claim we're dropping keeps the entry hashed. */
+ scoped_guard(spinlock, &super_dev_lock)
+ sd = super_dev_find(file_bdev(bdev_file)->bd_dev, sb);
+ if (sd)
+ super_dev_put(sd);
}
EXPORT_SYMBOL_GPL(fs_bdev_unregister);
@@ -1853,8 +1792,7 @@ int setup_bdev_super(struct super_block *sb, int sb_flags,
return -EACCES;
}
- /* The sget_fc() entry is already published; pairs with bdev_freeze(). */
- smp_mb();
+ /* sget_fc() hashed @sb, super_dev_lock orders that against bdev_freeze(). */
if (atomic_read(&bdev->bd_fsfreeze_count) > 0) {
if (fc)
warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
diff --git a/include/linux/fs/super_types.h b/include/linux/fs/super_types.h
index ecd96aeb1cee..72f4288e16c5 100644
--- a/include/linux/fs/super_types.h
+++ b/include/linux/fs/super_types.h
@@ -30,7 +30,6 @@ struct mount;
struct mtd_info;
struct quotactl_ops;
struct shrinker;
-struct super_dev;
struct unicode_map;
struct user_namespace;
struct workqueue_struct;
@@ -132,10 +131,18 @@ struct super_operations {
void (*report_error)(const struct fserror_event *event);
};
+/* A superblock's claim on a device, see fs/super.c. */
+struct super_dev {
+ struct hlist_node sd_hash;
+ struct super_block *sd_sb;
+ dev_t sd_dev;
+ unsigned int sd_claims;
+};
+
struct super_block {
struct list_head s_list; /* Keep this first */
dev_t s_dev; /* search index; _not_ kdev_t */
- struct super_dev *s_super_dev; /* sget_fc()'s device table claim */
+ struct super_dev s_super_dev; /* claim on s_dev */
unsigned char s_blocksize_bits;
unsigned long s_blocksize;
loff_t s_maxbytes; /* Max file size */
--
2.53.0
^ permalink raw reply related [flat|nested] 4+ messages in thread