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![Oleg Nesterov](/assets/img/avatar_default.png)
fput() and delayed_fput() can use llist and avoid the locking. This is unlikely path, it is not that this change can improve the performance, but this way the code looks simpler. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Suggested-by: Andrew Morton <akpm@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrey Vagin <avagin@openvz.org> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: David Howells <dhowells@redhat.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
487 lines
12 KiB
C
487 lines
12 KiB
C
/*
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* linux/fs/file_table.c
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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* Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
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*/
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#include <linux/string.h>
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#include <linux/slab.h>
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#include <linux/file.h>
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#include <linux/fdtable.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/fs.h>
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#include <linux/security.h>
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#include <linux/eventpoll.h>
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#include <linux/rcupdate.h>
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#include <linux/mount.h>
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#include <linux/capability.h>
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#include <linux/cdev.h>
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#include <linux/fsnotify.h>
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#include <linux/sysctl.h>
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#include <linux/lglock.h>
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#include <linux/percpu_counter.h>
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#include <linux/percpu.h>
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#include <linux/hardirq.h>
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#include <linux/task_work.h>
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#include <linux/ima.h>
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#include <linux/atomic.h>
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#include "internal.h"
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/* sysctl tunables... */
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struct files_stat_struct files_stat = {
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.max_files = NR_FILE
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};
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DEFINE_STATIC_LGLOCK(files_lglock);
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/* SLAB cache for file structures */
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static struct kmem_cache *filp_cachep __read_mostly;
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static struct percpu_counter nr_files __cacheline_aligned_in_smp;
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static void file_free_rcu(struct rcu_head *head)
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{
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struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
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put_cred(f->f_cred);
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kmem_cache_free(filp_cachep, f);
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}
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static inline void file_free(struct file *f)
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{
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percpu_counter_dec(&nr_files);
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file_check_state(f);
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call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
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}
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/*
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* Return the total number of open files in the system
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*/
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static long get_nr_files(void)
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{
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return percpu_counter_read_positive(&nr_files);
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}
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/*
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* Return the maximum number of open files in the system
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*/
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unsigned long get_max_files(void)
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{
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return files_stat.max_files;
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}
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EXPORT_SYMBOL_GPL(get_max_files);
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/*
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* Handle nr_files sysctl
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*/
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#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
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int proc_nr_files(ctl_table *table, int write,
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void __user *buffer, size_t *lenp, loff_t *ppos)
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{
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files_stat.nr_files = get_nr_files();
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return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
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}
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#else
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int proc_nr_files(ctl_table *table, int write,
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void __user *buffer, size_t *lenp, loff_t *ppos)
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{
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return -ENOSYS;
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}
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#endif
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/* Find an unused file structure and return a pointer to it.
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* Returns an error pointer if some error happend e.g. we over file
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* structures limit, run out of memory or operation is not permitted.
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*
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* Be very careful using this. You are responsible for
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* getting write access to any mount that you might assign
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* to this filp, if it is opened for write. If this is not
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* done, you will imbalance int the mount's writer count
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* and a warning at __fput() time.
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*/
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struct file *get_empty_filp(void)
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{
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const struct cred *cred = current_cred();
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static long old_max;
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struct file *f;
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int error;
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/*
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* Privileged users can go above max_files
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*/
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if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
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/*
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* percpu_counters are inaccurate. Do an expensive check before
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* we go and fail.
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*/
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if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
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goto over;
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}
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f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
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if (unlikely(!f))
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return ERR_PTR(-ENOMEM);
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percpu_counter_inc(&nr_files);
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f->f_cred = get_cred(cred);
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error = security_file_alloc(f);
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if (unlikely(error)) {
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file_free(f);
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return ERR_PTR(error);
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}
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INIT_LIST_HEAD(&f->f_u.fu_list);
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atomic_long_set(&f->f_count, 1);
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rwlock_init(&f->f_owner.lock);
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spin_lock_init(&f->f_lock);
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eventpoll_init_file(f);
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/* f->f_version: 0 */
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return f;
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over:
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/* Ran out of filps - report that */
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if (get_nr_files() > old_max) {
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pr_info("VFS: file-max limit %lu reached\n", get_max_files());
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old_max = get_nr_files();
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}
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return ERR_PTR(-ENFILE);
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}
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/**
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* alloc_file - allocate and initialize a 'struct file'
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* @mnt: the vfsmount on which the file will reside
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* @dentry: the dentry representing the new file
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* @mode: the mode with which the new file will be opened
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* @fop: the 'struct file_operations' for the new file
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*
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* Use this instead of get_empty_filp() to get a new
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* 'struct file'. Do so because of the same initialization
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* pitfalls reasons listed for init_file(). This is a
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* preferred interface to using init_file().
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*
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* If all the callers of init_file() are eliminated, its
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* code should be moved into this function.
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*/
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struct file *alloc_file(struct path *path, fmode_t mode,
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const struct file_operations *fop)
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{
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struct file *file;
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file = get_empty_filp();
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if (IS_ERR(file))
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return file;
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file->f_path = *path;
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file->f_inode = path->dentry->d_inode;
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file->f_mapping = path->dentry->d_inode->i_mapping;
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file->f_mode = mode;
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file->f_op = fop;
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/*
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* These mounts don't really matter in practice
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* for r/o bind mounts. They aren't userspace-
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* visible. We do this for consistency, and so
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* that we can do debugging checks at __fput()
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*/
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if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
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file_take_write(file);
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WARN_ON(mnt_clone_write(path->mnt));
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}
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if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
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i_readcount_inc(path->dentry->d_inode);
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return file;
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}
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EXPORT_SYMBOL(alloc_file);
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/**
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* drop_file_write_access - give up ability to write to a file
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* @file: the file to which we will stop writing
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*
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* This is a central place which will give up the ability
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* to write to @file, along with access to write through
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* its vfsmount.
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*/
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static void drop_file_write_access(struct file *file)
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{
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struct vfsmount *mnt = file->f_path.mnt;
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struct dentry *dentry = file->f_path.dentry;
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struct inode *inode = dentry->d_inode;
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put_write_access(inode);
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if (special_file(inode->i_mode))
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return;
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if (file_check_writeable(file) != 0)
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return;
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__mnt_drop_write(mnt);
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file_release_write(file);
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}
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/* the real guts of fput() - releasing the last reference to file
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*/
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static void __fput(struct file *file)
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{
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struct dentry *dentry = file->f_path.dentry;
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struct vfsmount *mnt = file->f_path.mnt;
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struct inode *inode = file->f_inode;
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might_sleep();
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fsnotify_close(file);
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/*
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* The function eventpoll_release() should be the first called
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* in the file cleanup chain.
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*/
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eventpoll_release(file);
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locks_remove_flock(file);
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if (unlikely(file->f_flags & FASYNC)) {
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if (file->f_op && file->f_op->fasync)
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file->f_op->fasync(-1, file, 0);
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}
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ima_file_free(file);
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if (file->f_op && file->f_op->release)
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file->f_op->release(inode, file);
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security_file_free(file);
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if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
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!(file->f_mode & FMODE_PATH))) {
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cdev_put(inode->i_cdev);
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}
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fops_put(file->f_op);
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put_pid(file->f_owner.pid);
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if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
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i_readcount_dec(inode);
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if (file->f_mode & FMODE_WRITE)
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drop_file_write_access(file);
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file->f_path.dentry = NULL;
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file->f_path.mnt = NULL;
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file->f_inode = NULL;
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file_free(file);
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dput(dentry);
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mntput(mnt);
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}
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static LLIST_HEAD(delayed_fput_list);
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static void delayed_fput(struct work_struct *unused)
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{
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struct llist_node *node = llist_del_all(&delayed_fput_list);
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struct llist_node *next;
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for (; node; node = next) {
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next = llist_next(node);
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__fput(llist_entry(node, struct file, f_u.fu_llist));
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}
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}
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static void ____fput(struct callback_head *work)
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{
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__fput(container_of(work, struct file, f_u.fu_rcuhead));
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}
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/*
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* If kernel thread really needs to have the final fput() it has done
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* to complete, call this. The only user right now is the boot - we
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* *do* need to make sure our writes to binaries on initramfs has
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* not left us with opened struct file waiting for __fput() - execve()
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* won't work without that. Please, don't add more callers without
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* very good reasons; in particular, never call that with locks
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* held and never call that from a thread that might need to do
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* some work on any kind of umount.
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*/
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void flush_delayed_fput(void)
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{
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delayed_fput(NULL);
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}
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static DECLARE_WORK(delayed_fput_work, delayed_fput);
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void fput(struct file *file)
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{
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if (atomic_long_dec_and_test(&file->f_count)) {
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struct task_struct *task = current;
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file_sb_list_del(file);
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if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
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init_task_work(&file->f_u.fu_rcuhead, ____fput);
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if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
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return;
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/*
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* After this task has run exit_task_work(),
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* task_work_add() will fail. free_ipc_ns()->
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* shm_destroy() can do this. Fall through to delayed
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* fput to avoid leaking *file.
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*/
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}
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if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
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schedule_work(&delayed_fput_work);
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}
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}
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/*
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* synchronous analog of fput(); for kernel threads that might be needed
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* in some umount() (and thus can't use flush_delayed_fput() without
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* risking deadlocks), need to wait for completion of __fput() and know
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* for this specific struct file it won't involve anything that would
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* need them. Use only if you really need it - at the very least,
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* don't blindly convert fput() by kernel thread to that.
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*/
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void __fput_sync(struct file *file)
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{
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if (atomic_long_dec_and_test(&file->f_count)) {
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struct task_struct *task = current;
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file_sb_list_del(file);
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BUG_ON(!(task->flags & PF_KTHREAD));
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__fput(file);
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}
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}
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EXPORT_SYMBOL(fput);
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void put_filp(struct file *file)
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{
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if (atomic_long_dec_and_test(&file->f_count)) {
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security_file_free(file);
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file_sb_list_del(file);
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file_free(file);
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}
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}
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static inline int file_list_cpu(struct file *file)
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{
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#ifdef CONFIG_SMP
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return file->f_sb_list_cpu;
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#else
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return smp_processor_id();
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#endif
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}
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/* helper for file_sb_list_add to reduce ifdefs */
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static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
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{
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struct list_head *list;
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#ifdef CONFIG_SMP
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int cpu;
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cpu = smp_processor_id();
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file->f_sb_list_cpu = cpu;
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list = per_cpu_ptr(sb->s_files, cpu);
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#else
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list = &sb->s_files;
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#endif
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list_add(&file->f_u.fu_list, list);
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}
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/**
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* file_sb_list_add - add a file to the sb's file list
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* @file: file to add
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* @sb: sb to add it to
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*
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* Use this function to associate a file with the superblock of the inode it
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* refers to.
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*/
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void file_sb_list_add(struct file *file, struct super_block *sb)
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{
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lg_local_lock(&files_lglock);
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__file_sb_list_add(file, sb);
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lg_local_unlock(&files_lglock);
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}
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/**
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* file_sb_list_del - remove a file from the sb's file list
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* @file: file to remove
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* @sb: sb to remove it from
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*
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* Use this function to remove a file from its superblock.
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*/
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void file_sb_list_del(struct file *file)
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{
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if (!list_empty(&file->f_u.fu_list)) {
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lg_local_lock_cpu(&files_lglock, file_list_cpu(file));
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list_del_init(&file->f_u.fu_list);
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lg_local_unlock_cpu(&files_lglock, file_list_cpu(file));
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}
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}
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#ifdef CONFIG_SMP
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/*
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* These macros iterate all files on all CPUs for a given superblock.
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* files_lglock must be held globally.
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*/
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#define do_file_list_for_each_entry(__sb, __file) \
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{ \
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int i; \
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for_each_possible_cpu(i) { \
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struct list_head *list; \
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list = per_cpu_ptr((__sb)->s_files, i); \
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list_for_each_entry((__file), list, f_u.fu_list)
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#define while_file_list_for_each_entry \
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} \
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}
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#else
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#define do_file_list_for_each_entry(__sb, __file) \
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{ \
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struct list_head *list; \
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list = &(sb)->s_files; \
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list_for_each_entry((__file), list, f_u.fu_list)
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#define while_file_list_for_each_entry \
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}
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#endif
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/**
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* mark_files_ro - mark all files read-only
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* @sb: superblock in question
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*
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* All files are marked read-only. We don't care about pending
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* delete files so this should be used in 'force' mode only.
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*/
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void mark_files_ro(struct super_block *sb)
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{
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struct file *f;
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lg_global_lock(&files_lglock);
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do_file_list_for_each_entry(sb, f) {
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if (!S_ISREG(file_inode(f)->i_mode))
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continue;
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if (!file_count(f))
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continue;
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if (!(f->f_mode & FMODE_WRITE))
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continue;
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spin_lock(&f->f_lock);
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f->f_mode &= ~FMODE_WRITE;
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spin_unlock(&f->f_lock);
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if (file_check_writeable(f) != 0)
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continue;
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__mnt_drop_write(f->f_path.mnt);
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file_release_write(f);
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} while_file_list_for_each_entry;
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lg_global_unlock(&files_lglock);
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}
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void __init files_init(unsigned long mempages)
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{
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unsigned long n;
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filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
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SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
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/*
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* One file with associated inode and dcache is very roughly 1K.
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* Per default don't use more than 10% of our memory for files.
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*/
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n = (mempages * (PAGE_SIZE / 1024)) / 10;
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files_stat.max_files = max_t(unsigned long, n, NR_FILE);
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files_defer_init();
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lg_lock_init(&files_lglock, "files_lglock");
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percpu_counter_init(&nr_files, 0);
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}
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