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: 's avatarDipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: 's avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: 's 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 @@ static int locate_fd(struct files_struct *files,
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);
......
This diff is collapsed.
......@@ -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>
/*
* The default fd array needs to be at least BITS_PER_LONG,
......@@ -23,6 +24,9 @@ struct fdtable {
struct file ** fd; /* current fd array */
fd_set *close_on_exec;
fd_set *open_fds;
struct rcu_head rcu;
struct files_struct *free_files;
struct fdtable *next;
};
/*
......@@ -31,13 +35,14 @@ struct fdtable {
struct files_struct {
atomic_t count;
spinlock_t file_lock; /* Protects all the below members. Nests inside tsk->alloc_lock */
struct fdtable *fdt;
struct fdtable fdtab;
fd_set close_on_exec_init;
fd_set open_fds_init;
struct file * fd_array[NR_OPEN_DEFAULT];
};
#define files_fdtable(files) (&(files)->fdtab)
#define files_fdtable(files) (rcu_dereference((files)->fdt))
extern void FASTCALL(__fput(struct file *));
extern void FASTCALL(fput(struct file *));
......@@ -65,6 +70,8 @@ extern fd_set *alloc_fdset(int);
extern void free_fdset(fd_set *, int);
extern int expand_files(struct files_struct *, int nr);
extern void free_fdtable(struct fdtable *fdt);
extern void __init files_defer_init(void);
static inline struct file * fcheck_files(struct files_struct *files, unsigned int fd)
{
......@@ -72,7 +79,7 @@ static inline struct file * fcheck_files(struct files_struct *files, unsigned in
struct fdtable *fdt = files_fdtable(files);
if (fd < fdt->max_fds)
file = fdt->fd[fd];
file = rcu_dereference(fdt->fd[fd]);
return file;
}
......
......@@ -9,6 +9,7 @@
#include <linux/config.h>
#include <linux/limits.h>
#include <linux/ioctl.h>
#include <linux/rcuref.h>
/*
* It's silly to have NR_OPEN bigger than NR_FILE, but you can change
......@@ -597,12 +598,13 @@ struct file {
spinlock_t f_ep_lock;
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
struct rcu_head f_rcuhead;
};
extern spinlock_t files_lock;
#define file_list_lock() spin_lock(&files_lock);
#define file_list_unlock() spin_unlock(&files_lock);
#define get_file(x) atomic_inc(&(x)->f_count)
#define get_file(x) rcuref_inc(&(x)->f_count)
#define file_count(x) atomic_read(&(x)->f_count)
#define MAX_NON_LFS ((1UL<<31) - 1)
......
......@@ -2,6 +2,7 @@
#define _LINUX__INIT_TASK_H
#include <linux/file.h>
#include <linux/rcupdate.h>
#define INIT_FDTABLE \
{ \
......@@ -11,12 +12,16 @@
.fd = &init_files.fd_array[0], \
.close_on_exec = &init_files.close_on_exec_init, \
.open_fds = &init_files.open_fds_init, \
.rcu = RCU_HEAD_INIT, \
.free_files = NULL, \
.next = NULL, \
}
#define INIT_FILES \
{ \
.count = ATOMIC_INIT(1), \
.file_lock = SPIN_LOCK_UNLOCKED, \
.fdt = &init_files.fdtab, \
.fdtab = INIT_FDTABLE, \
.close_on_exec_init = { { 0, } }, \
.open_fds_init = { { 0, } }, \
......
......@@ -411,15 +411,16 @@ void fastcall put_files_struct(struct files_struct *files)
close_files(files);
/*
* Free the fd and fdset arrays if we expanded them.
* If the fdtable was embedded, pass files for freeing
* at the end of the RCU grace period. Otherwise,
* you can free files immediately.
*/
fdt = files_fdtable(files);
if (fdt->fd != &files->fd_array[0])
free_fd_array(fdt->fd, fdt->max_fds);
if (fdt->max_fdset > __FD_SETSIZE) {
free_fdset(fdt->open_fds, fdt->max_fdset);
free_fdset(fdt->close_on_exec, fdt->max_fdset);
}
kmem_cache_free(files_cachep, files);
if (fdt == &files->fdtab)
fdt->free_files = files;
else
kmem_cache_free(files_cachep, files);
free_fdtable(fdt);
}
}
......
......@@ -35,6 +35,7 @@
#include <linux/syscalls.h>
#include <linux/jiffies.h>
#include <linux/futex.h>
#include <linux/rcupdate.h>
#include <linux/ptrace.h>
#include <linux/mount.h>
#include <linux/audit.h>
......@@ -565,13 +566,12 @@ static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
return 0;
}
static int count_open_files(struct files_struct *files, int size)
static int count_open_files(struct fdtable *fdt)
{
int size = fdt->max_fdset;
int i;
struct fdtable *fdt;
/* Find the last open fd */
fdt = files_fdtable(files);
for (i = size/(8*sizeof(long)); i > 0; ) {
if (fdt->open_fds->fds_bits[--i])
break;
......@@ -592,13 +592,17 @@ static struct files_struct *alloc_files(void)
atomic_set(&newf->count, 1);
spin_lock_init(&newf->file_lock);
fdt = files_fdtable(newf);
fdt = &newf->fdtab;
fdt->next_fd = 0;
fdt->max_fds = NR_OPEN_DEFAULT;
fdt->max_fdset = __FD_SETSIZE;
fdt->close_on_exec = &newf->close_on_exec_init;
fdt->open_fds = &newf->open_fds_init;
fdt->fd = &newf->fd_array[0];
INIT_RCU_HEAD(&fdt->rcu);
fdt->free_files = NULL;
fdt->next = NULL;
rcu_assign_pointer(newf->fdt, fdt);
out:
return newf;
}
......@@ -637,7 +641,7 @@ static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
old_fdt = files_fdtable(oldf);
new_fdt = files_fdtable(newf);
size = old_fdt->max_fdset;
open_files = count_open_files(oldf, old_fdt->max_fdset);
open_files = count_open_files(old_fdt);
expand = 0;
/*
......@@ -661,7 +665,14 @@ static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
spin_unlock(&newf->file_lock);
if (error < 0)
goto out_release;
new_fdt = files_fdtable(newf);
/*
* Reacquire the oldf lock and a pointer to its fd table
* who knows it may have a new bigger fd table. We need
* the latest pointer.
*/
spin_lock(&oldf->file_lock);
old_fdt = files_fdtable(oldf);
}
old_fds = old_fdt->fd;
......@@ -683,7 +694,7 @@ static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
*/
FD_CLR(open_files - i, new_fdt->open_fds);
}
*new_fds++ = f;
rcu_assign_pointer(*new_fds++, f);
}
spin_unlock(&oldf->file_lock);
......
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