[PATCH v3] proc: faster open/read/close with "permanent" files

Alexey Dobriyan
2020-02-22T20:15:50Z

Now that "struct proc_ops" exist we can start putting there stuff which
could not fly with VFS "struct file_operations"...

Most of fs/proc/inode.c file is dedicated to make open/read/.../close reliable
in the event of disappearing /proc entries which usually happens if module is
getting removed. Files like /proc/cpuinfo which never disappear simply do not
need such protection.

Save 2 atomic ops, 1 allocation, 1 free per open/read/close sequence for such
"permanent" files.

Enable "permanent" flag for

/proc/cpuinfo
/proc/kmsg
/proc/modules
/proc/slabinfo
/proc/stat
/proc/sysvipc/*
/proc/swaps

More will come once I figure out foolproof way to prevent out module
authors from marking their stuff "permanent" for performance reasons
when it is not.

This should help with scalability: benchmark is "read /proc/cpuinfo R times
by N threads scattered over the system".

N R t, s (before) t, s (after)
-----------------------------------------------------
64 4096 1.582458 1.530502 -3.2%
256 4096 6.371926 6.125168 -3.9%
1024 4096 25.64888 24.47528 -4.6%

Benchmark source:

#include <chrono>
#include <iostream>
#include <thread>
#include <vector>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

const int NR_CPUS = sysconf(_SC_NPROCESSORS_ONLN);
int N;
const char *filename;
int R;

int xxx = 0;

int glue(int n)
{
cpu_set_t m;
CPU_ZERO(&m);
CPU_SET(n, &m);
return sched_setaffinity(0, sizeof(cpu_set_t), &m);
}

void f(int n)
{
glue(n % NR_CPUS);

while (*(volatile int *)&xxx == 0) {
}

for (int i = 0; i < R; i++) {
int fd = open(filename, O_RDONLY);
char buf[4096];
ssize_t rv = read(fd, buf, sizeof(buf));
asm volatile ("" :: "g" (rv));
close(fd);
}
}

int main(int argc, char *argv[])
{
if (argc < 4) {
std::cerr << "usage: " << argv[0] << ' ' << "N /proc/filename R\n";
return 1;
}

N = atoi(argv[1]);
filename = argv[2];
R = atoi(argv[3]);

for (int i = 0; i < NR_CPUS; i++) {
if (glue(i) == 0)
break;
}

std::vector<std::thread> T;
T.reserve(N);
for (int i = 0; i < N; i++) {
T.emplace_back(f, i);
}

auto t0 = std::chrono::system_clock::now();
{
*(volatile int *)&xxx = 1;
for (auto& t: T) {
t.join();
}
}
auto t1 = std::chrono::system_clock::now();
std::chrono::duration<double> dt = t1 - t0;
std::cout << dt.count() << '\n';

return 0;
}

P.S.:
Explicit randomization marker is added because adding non-function pointer
will silently disable structure layout randomization.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
---

v2: fix unlock on error path
v3: more comments

fs/proc/cpuinfo.c | 1
fs/proc/generic.c | 33 +++++++-
fs/proc/inode.c | 187 +++++++++++++++++++++++++++++++++++-------------
fs/proc/internal.h | 6 +
fs/proc/kmsg.c | 1
fs/proc/stat.c | 1
include/linux/proc_fs.h | 17 ++++
ipc/util.c | 1
kernel/module.c | 1
mm/slab_common.c | 1
mm/swapfile.c | 1
11 files changed, 196 insertions(+), 54 deletions(-)

--- a/fs/proc/cpuinfo.c
+++ b/fs/proc/cpuinfo.c
@@ -17,6 +17,7 @@ static int cpuinfo_open(struct inode *inode, struct file *file)
}

static const struct proc_ops cpuinfo_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_open = cpuinfo_open,
.proc_read = seq_read,
.proc_lseek = seq_lseek,
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -531,6 +531,13 @@ struct proc_dir_entry *proc_create_reg(const char *name, umode_t mode,
return p;
}

+static inline void pde_set_flags(struct proc_dir_entry *pde)
+{
+ if (pde->proc_ops->proc_flags & PROC_ENTRY_PERMANENT) {
+ pde->flags |= PROC_ENTRY_PERMANENT;
+ }
+}
+
struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
struct proc_dir_entry *parent,
const struct proc_ops *proc_ops, void *data)
@@ -541,6 +548,7 @@ struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
if (!p)
return NULL;
p->proc_ops = proc_ops;
+ pde_set_flags(p);
return proc_register(parent, p);
}
EXPORT_SYMBOL(proc_create_data);
@@ -572,6 +580,7 @@ static int proc_seq_release(struct inode *inode, struct file *file)
}

static const struct proc_ops proc_seq_ops = {
+ /* not permanent -- can call into arbitrary seq_operations */
.proc_open = proc_seq_open,
.proc_read = seq_read,
.proc_lseek = seq_lseek,
@@ -602,6 +611,7 @@ static int proc_single_open(struct inode *inode, struct file *file)
}

static const struct proc_ops proc_single_ops = {
+ /* not permanent -- can call into arbitrary ->single_show */
.proc_open = proc_single_open,
.proc_read = seq_read,
.proc_lseek = seq_lseek,
@@ -662,9 +672,14 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)

de = pde_subdir_find(parent, fn, len);
if (de) {
- rb_erase(&de->subdir_node, &parent->subdir);
- if (S_ISDIR(de->mode)) {
- parent->nlink--;
+ if (unlikely(pde_is_permanent(de))) {
+ WARN(1, "removing permanent /proc entry '%s'", de->name);
+ de = NULL;
+ } else {
+ rb_erase(&de->subdir_node, &parent->subdir);
+ if (S_ISDIR(de->mode)) {
+ parent->nlink--;
+ }
}
}
write_unlock(&proc_subdir_lock);
@@ -700,12 +715,24 @@ int remove_proc_subtree(const char *name, struct proc_dir_entry *parent)
write_unlock(&proc_subdir_lock);
return -ENOENT;
}
+ if (unlikely(pde_is_permanent(root))) {
+ write_unlock(&proc_subdir_lock);
+ WARN(1, "removing permanent /proc entry '%s/%s'",
+ root->parent->name, root->name);
+ return -EINVAL;
+ }
rb_erase(&root->subdir_node, &parent->subdir);

de = root;
while (1) {
next = pde_subdir_first(de);
if (next) {
+ if (unlikely(pde_is_permanent(root))) {
+ write_unlock(&proc_subdir_lock);
+ WARN(1, "removing permanent /proc entry '%s/%s'",
+ next->parent->name, next->name);
+ return -EINVAL;
+ }
rb_erase(&next->subdir_node, &de->subdir);
de = next;
continue;
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -195,135 +195,204 @@ void proc_entry_rundown(struct proc_dir_entry *de)
spin_unlock(&de->pde_unload_lock);
}

+static loff_t pde_lseek(struct proc_dir_entry *pde, struct file *file, loff_t offset, int whence)
+{
+ typeof_member(struct proc_ops, proc_lseek) lseek;
+
+ lseek = pde->proc_ops->proc_lseek;
+ if (!lseek)
+ lseek = default_llseek;
+ return lseek(file, offset, whence);
+}
+
static loff_t proc_reg_llseek(struct file *file, loff_t offset, int whence)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
loff_t rv = -EINVAL;
- if (use_pde(pde)) {
- typeof_member(struct proc_ops, proc_lseek) lseek;

- lseek = pde->proc_ops->proc_lseek;
- if (!lseek)
- lseek = default_llseek;
- rv = lseek(file, offset, whence);
+ if (pde_is_permanent(pde)) {
+ return pde_lseek(pde, file, offset, whence);
+ } else if (use_pde(pde)) {
+ rv = pde_lseek(pde, file, offset, whence);
unuse_pde(pde);
}
return rv;
}

+static ssize_t pde_read(struct proc_dir_entry *pde, struct file *file, char __user *buf, size_t count, loff_t *ppos)
+{
+ typeof_member(struct proc_ops, proc_read) read;
+
+ read = pde->proc_ops->proc_read;
+ if (read)
+ return read(file, buf, count, ppos);
+ return -EIO;
+}
+
static ssize_t proc_reg_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
ssize_t rv = -EIO;
- if (use_pde(pde)) {
- typeof_member(struct proc_ops, proc_read) read;

- read = pde->proc_ops->proc_read;
- if (read)
- rv = read(file, buf, count, ppos);
+ if (pde_is_permanent(pde)) {
+ return pde_read(pde, file, buf, count, ppos);
+ } else if (use_pde(pde)) {
+ rv = pde_read(pde, file, buf, count, ppos);
unuse_pde(pde);
}
return rv;
}

+static ssize_t pde_write(struct proc_dir_entry *pde, struct file *file, const char __user *buf, size_t count, loff_t *ppos)
+{
+ typeof_member(struct proc_ops, proc_write) write;
+
+ write = pde->proc_ops->proc_write;
+ if (write)
+ return write(file, buf, count, ppos);
+ return -EIO;
+}
+
static ssize_t proc_reg_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
ssize_t rv = -EIO;
- if (use_pde(pde)) {
- typeof_member(struct proc_ops, proc_write) write;

- write = pde->proc_ops->proc_write;
- if (write)
- rv = write(file, buf, count, ppos);
+ if (pde_is_permanent(pde)) {
+ return pde_write(pde, file, buf, count, ppos);
+ } else if (use_pde(pde)) {
+ rv = pde_write(pde, file, buf, count, ppos);
unuse_pde(pde);
}
return rv;
}

+static __poll_t pde_poll(struct proc_dir_entry *pde, struct file *file, struct poll_table_struct *pts)
+{
+ typeof_member(struct proc_ops, proc_poll) poll;
+
+ poll = pde->proc_ops->proc_poll;
+ if (poll)
+ return poll(file, pts);
+ return DEFAULT_POLLMASK;
+}
+
static __poll_t proc_reg_poll(struct file *file, struct poll_table_struct *pts)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
__poll_t rv = DEFAULT_POLLMASK;
- if (use_pde(pde)) {
- typeof_member(struct proc_ops, proc_poll) poll;

- poll = pde->proc_ops->proc_poll;
- if (poll)
- rv = poll(file, pts);
+ if (pde_is_permanent(pde)) {
+ return pde_poll(pde, file, pts);
+ } else if (use_pde(pde)) {
+ rv = pde_poll(pde, file, pts);
unuse_pde(pde);
}
return rv;
}

+static long pde_ioctl(struct proc_dir_entry *pde, struct file *file, unsigned int cmd, unsigned long arg)
+{
+ typeof_member(struct proc_ops, proc_ioctl) ioctl;
+
+ ioctl = pde->proc_ops->proc_ioctl;
+ if (ioctl)
+ return ioctl(file, cmd, arg);
+ return -ENOTTY;
+}
+
static long proc_reg_unlocked_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
long rv = -ENOTTY;
- if (use_pde(pde)) {
- typeof_member(struct proc_ops, proc_ioctl) ioctl;

- ioctl = pde->proc_ops->proc_ioctl;
- if (ioctl)
- rv = ioctl(file, cmd, arg);
+ if (pde_is_permanent(pde)) {
+ return pde_ioctl(pde, file, cmd, arg);
+ } else if (use_pde(pde)) {
+ rv = pde_ioctl(pde, file, cmd, arg);
unuse_pde(pde);
}
return rv;
}

#ifdef CONFIG_COMPAT
+static long pde_compat_ioctl(struct proc_dir_entry *pde, struct file *file, unsigned int cmd, unsigned long arg)
+{
+ typeof_member(struct proc_ops, proc_compat_ioctl) compat_ioctl;
+
+ compat_ioctl = pde->proc_ops->proc_compat_ioctl;
+ if (compat_ioctl)
+ return compat_ioctl(file, cmd, arg);
+ return -ENOTTY;
+}
+
static long proc_reg_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
long rv = -ENOTTY;
- if (use_pde(pde)) {
- typeof_member(struct proc_ops, proc_compat_ioctl) compat_ioctl;
-
- compat_ioctl = pde->proc_ops->proc_compat_ioctl;
- if (compat_ioctl)
- rv = compat_ioctl(file, cmd, arg);
+ if (pde_is_permanent(pde)) {
+ return pde_compat_ioctl(pde, file, cmd, arg);
+ } else if (use_pde(pde)) {
+ rv = pde_compat_ioctl(pde, file, cmd, arg);
unuse_pde(pde);
}
return rv;
}
#endif

+static int pde_mmap(struct proc_dir_entry *pde, struct file *file, struct vm_area_struct *vma)
+{
+ typeof_member(struct proc_ops, proc_mmap) mmap;
+
+ mmap = pde->proc_ops->proc_mmap;
+ if (mmap)
+ return mmap(file, vma);
+ return -EIO;
+}
+
static int proc_reg_mmap(struct file *file, struct vm_area_struct *vma)
{
struct proc_dir_entry *pde = PDE(file_inode(file));
int rv = -EIO;
- if (use_pde(pde)) {
- typeof_member(struct proc_ops, proc_mmap) mmap;

- mmap = pde->proc_ops->proc_mmap;
- if (mmap)
- rv = mmap(file, vma);
+ if (pde_is_permanent(pde)) {
+ return pde_mmap(pde, file, vma);
+ } else if (use_pde(pde)) {
+ rv = pde_mmap(pde, file, vma);
unuse_pde(pde);
}
return rv;
}

static unsigned long
-proc_reg_get_unmapped_area(struct file *file, unsigned long orig_addr,
+pde_get_unmapped_area(struct proc_dir_entry *pde, struct file *file, unsigned long orig_addr,
unsigned long len, unsigned long pgoff,
unsigned long flags)
{
- struct proc_dir_entry *pde = PDE(file_inode(file));
- unsigned long rv = -EIO;
-
- if (use_pde(pde)) {
- typeof_member(struct proc_ops, proc_get_unmapped_area) get_area;
+ typeof_member(struct proc_ops, proc_get_unmapped_area) get_area;

- get_area = pde->proc_ops->proc_get_unmapped_area;
+ get_area = pde->proc_ops->proc_get_unmapped_area;
#ifdef CONFIG_MMU
- if (!get_area)
- get_area = current->mm->get_unmapped_area;
+ if (!get_area)
+ get_area = current->mm->get_unmapped_area;
#endif
+ if (get_area)
+ return get_area(file, orig_addr, len, pgoff, flags);
+ return orig_addr;
+}
+
+static unsigned long
+proc_reg_get_unmapped_area(struct file *file, unsigned long orig_addr,
+ unsigned long len, unsigned long pgoff,
+ unsigned long flags)
+{
+ struct proc_dir_entry *pde = PDE(file_inode(file));
+ unsigned long rv = -EIO;

- if (get_area)
- rv = get_area(file, orig_addr, len, pgoff, flags);
- else
- rv = orig_addr;
+ if (pde_is_permanent(pde)) {
+ return pde_get_unmapped_area(pde, file, orig_addr, len, pgoff, flags);
+ } else if (use_pde(pde)) {
+ rv = pde_get_unmapped_area(pde, file, orig_addr, len, pgoff, flags);
unuse_pde(pde);
}
return rv;
@@ -337,6 +406,13 @@ static int proc_reg_open(struct inode *inode, struct file *file)
typeof_member(struct proc_ops, proc_release) release;
struct pde_opener *pdeo;

+ if (pde_is_permanent(pde)) {
+ open = pde->proc_ops->proc_open;
+ if (open)
+ rv = open(inode, file);
+ return rv;
+ }
+
/*
* Ensure that
* 1) PDE's ->release hook will be called no matter what
@@ -386,6 +462,17 @@ static int proc_reg_release(struct inode *inode, struct file *file)
{
struct proc_dir_entry *pde = PDE(inode);
struct pde_opener *pdeo;
+
+ if (pde_is_permanent(pde)) {
+ typeof_member(struct proc_ops, proc_release) release;
+
+ release = pde->proc_ops->proc_release;
+ if (release) {
+ return release(inode, file);
+ }
+ return 0;
+ }
+
spin_lock(&pde->pde_unload_lock);
list_for_each_entry(pdeo, &pde->pde_openers, lh) {
if (pdeo->file == file) {
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -61,6 +61,7 @@ struct proc_dir_entry {
struct rb_node subdir_node;
char *name;
umode_t mode;
+ u8 flags;
u8 namelen;
char inline_name[];
} __randomize_layout;
@@ -73,6 +74,11 @@ struct proc_dir_entry {
0)
#define SIZEOF_PDE_INLINE_NAME (SIZEOF_PDE - sizeof(struct proc_dir_entry))

+static inline bool pde_is_permanent(const struct proc_dir_entry *pde)
+{
+ return pde->flags & PROC_ENTRY_PERMANENT;
+}
+
extern struct kmem_cache *proc_dir_entry_cache;
void pde_free(struct proc_dir_entry *pde);

--- a/fs/proc/kmsg.c
+++ b/fs/proc/kmsg.c
@@ -50,6 +50,7 @@ static __poll_t kmsg_poll(struct file *file, poll_table *wait)

static const struct proc_ops kmsg_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_read = kmsg_read,
.proc_poll = kmsg_poll,
.proc_open = kmsg_open,
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -224,6 +224,7 @@ static int stat_open(struct inode *inode, struct file *file)
}

static const struct proc_ops stat_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_open = stat_open,
.proc_read = seq_read,
.proc_lseek = seq_lseek,
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -5,6 +5,7 @@
#ifndef _LINUX_PROC_FS_H
#define _LINUX_PROC_FS_H

+#include <linux/compiler.h>
#include <linux/types.h>
#include <linux/fs.h>

@@ -12,7 +13,21 @@ struct proc_dir_entry;
struct seq_file;
struct seq_operations;

+enum {
+ /*
+ * All /proc entries using this ->proc_ops instance are never removed.
+ *
+ * If in doubt, ignore this flag.
+ */
+#ifdef MODULE
+ PROC_ENTRY_PERMANENT = 0U,
+#else
+ PROC_ENTRY_PERMANENT = 1U << 0,
+#endif
+};
+
struct proc_ops {
+ unsigned int proc_flags;
int (*proc_open)(struct inode *, struct file *);
ssize_t (*proc_read)(struct file *, char __user *, size_t, loff_t *);
ssize_t (*proc_write)(struct file *, const char __user *, size_t, loff_t *);
@@ -25,7 +40,7 @@ struct proc_ops {
#endif
int (*proc_mmap)(struct file *, struct vm_area_struct *);
unsigned long (*proc_get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
-};
+} __randomize_layout;

#ifdef CONFIG_PROC_FS

--- a/ipc/util.c
+++ b/ipc/util.c
@@ -885,6 +885,7 @@ static int sysvipc_proc_release(struct inode *inode, struct file *file)
}

static const struct proc_ops sysvipc_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_open = sysvipc_proc_open,
.proc_read = seq_read,
.proc_lseek = seq_lseek,
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4355,6 +4355,7 @@ static int modules_open(struct inode *inode, struct file *file)
}

static const struct proc_ops modules_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_open = modules_open,
.proc_read = seq_read,
.proc_lseek = seq_lseek,
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1581,6 +1581,7 @@ static int slabinfo_open(struct inode *inode, struct file *file)
}

static const struct proc_ops slabinfo_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_open = slabinfo_open,
.proc_read = seq_read,
.proc_write = slabinfo_write,
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2797,6 +2797,7 @@ static int swaps_open(struct inode *inode, struct file *file)
}

static const struct proc_ops swaps_proc_ops = {
+ .proc_flags = PROC_ENTRY_PERMANENT,
.proc_open = swaps_open,
.proc_read = seq_read,
.proc_lseek = seq_lseek,