Commit ab2af1f5 authored by Dipankar Sarma's avatar Dipankar Sarma Committed by Linus Torvalds

[PATCH] files: files struct with RCU

Patch to eliminate struct files_struct.file_lock spinlock on the reader side
and use rcu refcounting rcuref_xxx api for the f_count refcounter.  The
updates to the fdtable are done by allocating a new fdtable structure and
setting files->fdt to point to the new structure.  The fdtable structure is
protected by RCU thereby allowing lock-free lookup.  For fd arrays/sets that
are vmalloced, we use keventd to free them since RCU callbacks can't sleep.  A
global list of fdtable to be freed is not scalable, so we use a per-cpu list.
If keventd is already handling the current cpu's work, we use a timer to defer
queueing of that work.

Since the last publication, this patch has been re-written to avoid using
explicit memory barriers and use rcu_assign_pointer(), rcu_dereference()
premitives instead.  This required that the fd information is kept in a
separate structure (fdtable) and updated atomically.
Signed-off-by: default avatarDipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 6e72ad2c
......@@ -29,6 +29,7 @@
#include <linux/highmem.h>
#include <linux/workqueue.h>
#include <linux/security.h>
#include <linux/rcuref.h>
#include <asm/kmap_types.h>
#include <asm/uaccess.h>
......@@ -499,7 +500,7 @@ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req)
/* Must be done under the lock to serialise against cancellation.
* Call this aio_fput as it duplicates fput via the fput_work.
*/
if (unlikely(atomic_dec_and_test(&req->ki_filp->f_count))) {
if (unlikely(rcuref_dec_and_test(&req->ki_filp->f_count))) {
get_ioctx(ctx);
spin_lock(&fput_lock);
list_add(&req->ki_list, &fput_head);
......
......@@ -16,6 +16,7 @@
#include <linux/security.h>
#include <linux/ptrace.h>
#include <linux/signal.h>
#include <linux/rcupdate.h>
#include <asm/poll.h>
#include <asm/siginfo.h>
......@@ -64,8 +65,8 @@ static int locate_fd(struct files_struct *files,
if (orig_start >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
goto out;
fdt = files_fdtable(files);
repeat:
fdt = files_fdtable(files);
/*
* Someone might have closed fd's in the range
* orig_start..fdt->next_fd
......@@ -95,9 +96,15 @@ repeat:
if (error)
goto repeat;
/*
* We reacquired files_lock, so we are safe as long as
* we reacquire the fdtable pointer and use it while holding
* the lock, no one can free it during that time.
*/
fdt = files_fdtable(files);
if (start <= fdt->next_fd)
fdt->next_fd = newfd + 1;
error = newfd;
out:
......@@ -163,7 +170,7 @@ asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
if (!tofree && FD_ISSET(newfd, fdt->open_fds))
goto out_fput;
fdt->fd[newfd] = file;
rcu_assign_pointer(fdt->fd[newfd], file);
FD_SET(newfd, fdt->open_fds);
FD_CLR(newfd, fdt->close_on_exec);
spin_unlock(&files->file_lock);
......
......@@ -13,6 +13,25 @@
#include <linux/vmalloc.h>
#include <linux/file.h>
#include <linux/bitops.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/workqueue.h>
struct fdtable_defer {
spinlock_t lock;
struct work_struct wq;
struct timer_list timer;
struct fdtable *next;
};
/*
* We use this list to defer free fdtables that have vmalloced
* sets/arrays. By keeping a per-cpu list, we avoid having to embed
* the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
* this per-task structure.
*/
static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
/*
......@@ -48,85 +67,143 @@ void free_fd_array(struct file **array, int num)
vfree(array);
}
/*
* Expand the fd array in the files_struct. Called with the files
* spinlock held for write.
*/
static int expand_fd_array(struct files_struct *files, int nr)
__releases(files->file_lock)
__acquires(files->file_lock)
static void __free_fdtable(struct fdtable *fdt)
{
struct file **new_fds;
int error, nfds;
struct fdtable *fdt;
int fdset_size, fdarray_size;
error = -EMFILE;
fdt = files_fdtable(files);
if (fdt->max_fds >= NR_OPEN || nr >= NR_OPEN)
goto out;
fdset_size = fdt->max_fdset / 8;
fdarray_size = fdt->max_fds * sizeof(struct file *);
free_fdset(fdt->open_fds, fdset_size);
free_fdset(fdt->close_on_exec, fdset_size);
free_fd_array(fdt->fd, fdarray_size);
kfree(fdt);
}
nfds = fdt->max_fds;
spin_unlock(&files->file_lock);
static void fdtable_timer(unsigned long data)
{
struct fdtable_defer *fddef = (struct fdtable_defer *)data;
/*
* Expand to the max in easy steps, and keep expanding it until
* we have enough for the requested fd array size.
spin_lock(&fddef->lock);
/*
* If someone already emptied the queue return.
*/
if (!fddef->next)
goto out;
if (!schedule_work(&fddef->wq))
mod_timer(&fddef->timer, 5);
out:
spin_unlock(&fddef->lock);
}
do {
#if NR_OPEN_DEFAULT < 256
if (nfds < 256)
nfds = 256;
else
#endif
if (nfds < (PAGE_SIZE / sizeof(struct file *)))
nfds = PAGE_SIZE / sizeof(struct file *);
else {
nfds = nfds * 2;
if (nfds > NR_OPEN)
nfds = NR_OPEN;
}
} while (nfds <= nr);
static void free_fdtable_work(struct fdtable_defer *f)
{
struct fdtable *fdt;
error = -ENOMEM;
new_fds = alloc_fd_array(nfds);
spin_lock(&files->file_lock);
if (!new_fds)
goto out;
spin_lock_bh(&f->lock);
fdt = f->next;
f->next = NULL;
spin_unlock_bh(&f->lock);
while(fdt) {
struct fdtable *next = fdt->next;
__free_fdtable(fdt);
fdt = next;
}
}
/* Copy the existing array and install the new pointer */
fdt = files_fdtable(files);
static void free_fdtable_rcu(struct rcu_head *rcu)
{
struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
int fdset_size, fdarray_size;
struct fdtable_defer *fddef;
if (nfds > fdt->max_fds) {
struct file **old_fds;
int i;
old_fds = xchg(&fdt->fd, new_fds);
i = xchg(&fdt->max_fds, nfds);
/* Don't copy/clear the array if we are creating a new
fd array for fork() */
if (i) {
memcpy(new_fds, old_fds, i * sizeof(struct file *));
/* clear the remainder of the array */
memset(&new_fds[i], 0,
(nfds-i) * sizeof(struct file *));
spin_unlock(&files->file_lock);
free_fd_array(old_fds, i);
spin_lock(&files->file_lock);
}
BUG_ON(!fdt);
fdset_size = fdt->max_fdset / 8;
fdarray_size = fdt->max_fds * sizeof(struct file *);
if (fdt->free_files) {
/*
* The this fdtable was embedded in the files structure
* and the files structure itself was getting destroyed.
* It is now safe to free the files structure.
*/
kmem_cache_free(files_cachep, fdt->free_files);
return;
}
if (fdt->max_fdset <= __FD_SETSIZE && fdt->max_fds <= NR_OPEN_DEFAULT) {
/*
* The fdtable was embedded
*/
return;
}
if (fdset_size <= PAGE_SIZE && fdarray_size <= PAGE_SIZE) {
kfree(fdt->open_fds);
kfree(fdt->close_on_exec);
kfree(fdt->fd);
kfree(fdt);
} else {
/* Somebody expanded the array while we slept ... */
spin_unlock(&files->file_lock);
free_fd_array(new_fds, nfds);
spin_lock(&files->file_lock);
fddef = &get_cpu_var(fdtable_defer_list);
spin_lock(&fddef->lock);
fdt->next = fddef->next;
fddef->next = fdt;
/*
* vmallocs are handled from the workqueue context.
* If the per-cpu workqueue is running, then we
* defer work scheduling through a timer.
*/
if (!schedule_work(&fddef->wq))
mod_timer(&fddef->timer, 5);
spin_unlock(&fddef->lock);
put_cpu_var(fdtable_defer_list);
}
error = 0;
out:
return error;
}
void free_fdtable(struct fdtable *fdt)
{
if (fdt->free_files || fdt->max_fdset > __FD_SETSIZE ||
fdt->max_fds > NR_OPEN_DEFAULT)
call_rcu(&fdt->rcu, free_fdtable_rcu);
}
/*
* Expand the fdset in the files_struct. Called with the files spinlock
* held for write.
*/
static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
{
int i;
int count;
BUG_ON(nfdt->max_fdset < fdt->max_fdset);
BUG_ON(nfdt->max_fds < fdt->max_fds);
/* Copy the existing tables and install the new pointers */
i = fdt->max_fdset / (sizeof(unsigned long) * 8);
count = (nfdt->max_fdset - fdt->max_fdset) / 8;
/*
* Don't copy the entire array if the current fdset is
* not yet initialised.
*/
if (i) {
memcpy (nfdt->open_fds, fdt->open_fds,
fdt->max_fdset/8);
memcpy (nfdt->close_on_exec, fdt->close_on_exec,
fdt->max_fdset/8);
memset (&nfdt->open_fds->fds_bits[i], 0, count);
memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
}
/* Don't copy/clear the array if we are creating a new
fd array for fork() */
if (fdt->max_fds) {
memcpy(nfdt->fd, fdt->fd,
fdt->max_fds * sizeof(struct file *));
/* clear the remainder of the array */
memset(&nfdt->fd[fdt->max_fds], 0,
(nfdt->max_fds - fdt->max_fds) *
sizeof(struct file *));
}
nfdt->next_fd = fdt->next_fd;
}
/*
......@@ -157,28 +234,21 @@ void free_fdset(fd_set *array, int num)
vfree(array);
}
/*
* Expand the fdset in the files_struct. Called with the files spinlock
* held for write.
*/
static int expand_fdset(struct files_struct *files, int nr)
__releases(file->file_lock)
__acquires(file->file_lock)
static struct fdtable *alloc_fdtable(int nr)
{
fd_set *new_openset = NULL, *new_execset = NULL;
int error, nfds = 0;
struct fdtable *fdt;
error = -EMFILE;
fdt = files_fdtable(files);
if (fdt->max_fdset >= NR_OPEN || nr >= NR_OPEN)
goto out;
struct fdtable *fdt = NULL;
int nfds = 0;
fd_set *new_openset = NULL, *new_execset = NULL;
struct file **new_fds;
nfds = fdt->max_fdset;
spin_unlock(&files->file_lock);
fdt = kmalloc(sizeof(*fdt), GFP_KERNEL);
if (!fdt)
goto out;
memset(fdt, 0, sizeof(*fdt));
/* Expand to the max in easy steps */
do {
nfds = __FD_SETSIZE;
/* Expand to the max in easy steps */
do {
if (nfds < (PAGE_SIZE * 8))
nfds = PAGE_SIZE * 8;
else {
......@@ -188,50 +258,88 @@ static int expand_fdset(struct files_struct *files, int nr)
}
} while (nfds <= nr);
error = -ENOMEM;
new_openset = alloc_fdset(nfds);
new_execset = alloc_fdset(nfds);
spin_lock(&files->file_lock);
if (!new_openset || !new_execset)
new_openset = alloc_fdset(nfds);
new_execset = alloc_fdset(nfds);
if (!new_openset || !new_execset)
goto out;
fdt->open_fds = new_openset;
fdt->close_on_exec = new_execset;
fdt->max_fdset = nfds;
nfds = NR_OPEN_DEFAULT;
/*
* Expand to the max in easy steps, and keep expanding it until
* we have enough for the requested fd array size.
*/
do {
#if NR_OPEN_DEFAULT < 256
if (nfds < 256)
nfds = 256;
else
#endif
if (nfds < (PAGE_SIZE / sizeof(struct file *)))
nfds = PAGE_SIZE / sizeof(struct file *);
else {
nfds = nfds * 2;
if (nfds > NR_OPEN)
nfds = NR_OPEN;
}
} while (nfds <= nr);
new_fds = alloc_fd_array(nfds);
if (!new_fds)
goto out;
fdt->fd = new_fds;
fdt->max_fds = nfds;
fdt->free_files = NULL;
return fdt;
out:
if (new_openset)
free_fdset(new_openset, nfds);
if (new_execset)
free_fdset(new_execset, nfds);
kfree(fdt);
return NULL;
}
error = 0;
/* Copy the existing tables and install the new pointers */
/*
* Expands the file descriptor table - it will allocate a new fdtable and
* both fd array and fdset. It is expected to be called with the
* files_lock held.
*/
static int expand_fdtable(struct files_struct *files, int nr)
__releases(files->file_lock)
__acquires(files->file_lock)
{
int error = 0;
struct fdtable *fdt;
struct fdtable *nfdt = NULL;
spin_unlock(&files->file_lock);
nfdt = alloc_fdtable(nr);
if (!nfdt) {
error = -ENOMEM;
spin_lock(&files->file_lock);
goto out;
}
spin_lock(&files->file_lock);
fdt = files_fdtable(files);
if (nfds > fdt->max_fdset) {
int i = fdt->max_fdset / (sizeof(unsigned long) * 8);
int count = (nfds - fdt->max_fdset) / 8;
/*
* Don't copy the entire array if the current fdset is
* not yet initialised.
*/
if (i) {
memcpy (new_openset, fdt->open_fds, fdt->max_fdset/8);
memcpy (new_execset, fdt->close_on_exec, fdt->max_fdset/8);
memset (&new_openset->fds_bits[i], 0, count);
memset (&new_execset->fds_bits[i], 0, count);
}
nfds = xchg(&fdt->max_fdset, nfds);
new_openset = xchg(&fdt->open_fds, new_openset);
new_execset = xchg(&fdt->close_on_exec, new_execset);
/*
* Check again since another task may have expanded the
* fd table while we dropped the lock
*/
if (nr >= fdt->max_fds || nr >= fdt->max_fdset) {
copy_fdtable(nfdt, fdt);
} else {
/* Somebody expanded while we dropped file_lock */
spin_unlock(&files->file_lock);
free_fdset (new_openset, nfds);
free_fdset (new_execset, nfds);
__free_fdtable(nfdt);
spin_lock(&files->file_lock);
return 0;
}
/* Somebody expanded the array while we slept ... */
goto out;
}
rcu_assign_pointer(files->fdt, nfdt);
free_fdtable(fdt);
out:
spin_unlock(&files->file_lock);
if (new_openset)
free_fdset(new_openset, nfds);
if (new_execset)
free_fdset(new_execset, nfds);
spin_lock(&files->file_lock);
return error;
}
......@@ -246,17 +354,36 @@ int expand_files(struct files_struct *files, int nr)
struct fdtable *fdt;
fdt = files_fdtable(files);
if (nr >= fdt->max_fdset) {
expand = 1;
if ((err = expand_fdset(files, nr)))
if (nr >= fdt->max_fdset || nr >= fdt->max_fds) {
if (fdt->max_fdset >= NR_OPEN ||
fdt->max_fds >= NR_OPEN || nr >= NR_OPEN) {
err = -EMFILE;
goto out;
}
if (nr >= fdt->max_fds) {
}
expand = 1;
if ((err = expand_fd_array(files, nr)))
if ((err = expand_fdtable(files, nr)))
goto out;
}
err = expand;
out:
return err;
}
static void __devinit fdtable_defer_list_init(int cpu)
{
struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
spin_lock_init(&fddef->lock);
INIT_WORK(&fddef->wq, (void (*)(void *))free_fdtable_work, fddef);
init_timer(&fddef->timer);
fddef->timer.data = (unsigned long)fddef;
fddef->timer.function = fdtable_timer;
fddef->next = NULL;
}
void __init files_defer_init(void)
{
int i;
/* Really early - can't use for_each_cpu */
for (i = 0; i < NR_CPUS; i++)
fdtable_defer_list_init(i);
}
......@@ -14,6 +14,7 @@
#include <linux/fs.h>
#include <linux/security.h>
#include <linux/eventpoll.h>
#include <linux/rcupdate.h>
#include <linux/mount.h>
#include <linux/cdev.h>
#include <linux/fsnotify.h>
......@@ -53,11 +54,17 @@ void filp_dtor(void * objp, struct kmem_cache_s *cachep, unsigned long dflags)
spin_unlock_irqrestore(&filp_count_lock, flags);
}
static inline void file_free(struct file *f)
static inline void file_free_rcu(struct rcu_head *head)
{
struct file *f = container_of(head, struct file, f_rcuhead);
kmem_cache_free(filp_cachep, f);
}
static inline void file_free(struct file *f)
{
call_rcu(&f->f_rcuhead, file_free_rcu);
}
/* Find an unused file structure and return a pointer to it.
* Returns NULL, if there are no more free file structures or
* we run out of memory.
......@@ -110,7 +117,7 @@ EXPORT_SYMBOL(get_empty_filp);
void fastcall fput(struct file *file)
{
if (atomic_dec_and_test(&file->f_count))
if (rcuref_dec_and_test(&file->f_count))
__fput(file);
}
......@@ -156,11 +163,17 @@ struct file fastcall *fget(unsigned int fd)
struct file *file;
struct files_struct *files = current->files;
spin_lock(&files->file_lock);
rcu_read_lock();
file = fcheck_files(files, fd);
if (file)
get_file(file);
spin_unlock(&files->file_lock);
if (file) {
if (!rcuref_inc_lf(&file->f_count)) {
/* File object ref couldn't be taken */
rcu_read_unlock();
return NULL;
}
}
rcu_read_unlock();
return file;
}
......@@ -182,21 +195,25 @@ struct file fastcall *fget_light(unsigned int fd, int *fput_needed)
if (likely((atomic_read(&files->count) == 1))) {
file = fcheck_files(files, fd);
} else {
spin_lock(&files->file_lock);
rcu_read_lock();
file = fcheck_files(files, fd);
if (file) {
get_file(file);
*fput_needed = 1;
if (rcuref_inc_lf(&file->f_count))
*fput_needed = 1;
else
/* Didn't get the reference, someone's freed */
file = NULL;
}
spin_unlock(&files->file_lock);
rcu_read_unlock();
}
return file;
}
void put_filp(struct file *file)
{
if (atomic_dec_and_test(&file->f_count)) {
if (rcuref_dec_and_test(&file->f_count)) {
security_file_free(file);
file_kill(file);
file_free(file);
......@@ -257,4 +274,5 @@ void __init files_init(unsigned long mempages)
files_stat.max_files = n;
if (files_stat.max_files < NR_FILE)
files_stat.max_files = NR_FILE;
files_defer_init();
}
......@@ -24,6 +24,7 @@
#include <linux/personality.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
#include <linux/rcupdate.h>
#include <asm/unistd.h>
......@@ -930,9 +931,8 @@ void fastcall fd_install(unsigned int fd, struct file * file)
struct fdtable *fdt;
spin_lock(&files->file_lock);
fdt = files_fdtable(files);
if (unlikely(fdt->fd[fd] != NULL))
BUG();
fdt->fd[fd] = file;
BUG_ON(fdt->fd[fd] != NULL);
rcu_assign_pointer(fdt->fd[fd], file);
spin_unlock(&files->file_lock);
}
......@@ -1024,7 +1024,7 @@ asmlinkage long sys_close(unsigned int fd)
filp = fdt->fd[fd];
if (!filp)
goto out_unlock;
fdt->fd[fd] = NULL;
rcu_assign_pointer(fdt->fd[fd], NULL);
FD_CLR(fd, fdt->close_on_exec);
__put_unused_fd(files, fd);
spin_unlock(&files->file_lock);
......
......@@ -9,6 +9,7 @@
#include <linux/posix_types.h>
#include <linux/compiler.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
<