root/fs/fs-writeback.c
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DEFINITIONS
This source file includes following definitions.
- writeback_acquire
- writeback_in_progress
- writeback_release
- __mark_inode_dirty
- write_inode
- redirty_tail
- requeue_io
- inode_sync_complete
- move_expired_inodes
- queue_io
- sb_has_dirty_inodes
- __sync_single_inode
- __writeback_single_inode
- generic_sync_sb_inodes
- sync_sb_inodes
- writeback_inodes
- sync_inodes_sb
- set_sb_syncing
- __sync_inodes
- sync_inodes
- write_inode_now
- sync_inode
- generic_osync_inode
/*
* fs/fs-writeback.c
*
* Copyright (C) 2002, Linus Torvalds.
*
* Contains all the functions related to writing back and waiting
* upon dirty inodes against superblocks, and writing back dirty
* pages against inodes. ie: data writeback. Writeout of the
* inode itself is not handled here.
*
* 10Apr2002 akpm@zip.com.au
* Split out of fs/inode.c
* Additions for address_space-based writeback
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/buffer_head.h>
#include "internal.h"
/**
* writeback_acquire - attempt to get exclusive writeback access to a device
* @bdi: the device's backing_dev_info structure
*
* It is a waste of resources to have more than one pdflush thread blocked on
* a single request queue. Exclusion at the request_queue level is obtained
* via a flag in the request_queue's backing_dev_info.state.
*
* Non-request_queue-backed address_spaces will share default_backing_dev_info,
* unless they implement their own. Which is somewhat inefficient, as this
* may prevent concurrent writeback against multiple devices.
*/
static int writeback_acquire(struct backing_dev_info *bdi)
{
return !test_and_set_bit(BDI_pdflush, &bdi->state);
}
/**
* writeback_in_progress - determine whether there is writeback in progress
* @bdi: the device's backing_dev_info structure.
*
* Determine whether there is writeback in progress against a backing device.
*/
int writeback_in_progress(struct backing_dev_info *bdi)
{
return test_bit(BDI_pdflush, &bdi->state);
}
/**
* writeback_release - relinquish exclusive writeback access against a device.
* @bdi: the device's backing_dev_info structure
*/
static void writeback_release(struct backing_dev_info *bdi)
{
BUG_ON(!writeback_in_progress(bdi));
clear_bit(BDI_pdflush, &bdi->state);
}
/**
* __mark_inode_dirty - internal function
* @inode: inode to mark
* @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
* Mark an inode as dirty. Callers should use mark_inode_dirty or
* mark_inode_dirty_sync.
*
* Put the inode on the super block's dirty list.
*
* CAREFUL! We mark it dirty unconditionally, but move it onto the
* dirty list only if it is hashed or if it refers to a blockdev.
* If it was not hashed, it will never be added to the dirty list
* even if it is later hashed, as it will have been marked dirty already.
*
* In short, make sure you hash any inodes _before_ you start marking
* them dirty.
*
* This function *must* be atomic for the I_DIRTY_PAGES case -
* set_page_dirty() is called under spinlock in several places.
*
* Note that for blockdevs, inode->dirtied_when represents the dirtying time of
* the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
* the kernel-internal blockdev inode represents the dirtying time of the
* blockdev's pages. This is why for I_DIRTY_PAGES we always use
* page->mapping->host, so the page-dirtying time is recorded in the internal
* blockdev inode.
*/
void __mark_inode_dirty(struct inode *inode, int flags)
{
struct super_block *sb = inode->i_sb;
/*
* Don't do this for I_DIRTY_PAGES - that doesn't actually
* dirty the inode itself
*/
if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
if (sb->s_op->dirty_inode)
sb->s_op->dirty_inode(inode);
}
/*
* make sure that changes are seen by all cpus before we test i_state
* -- mikulas
*/
smp_mb();
/* avoid the locking if we can */
if ((inode->i_state & flags) == flags)
return;
if (unlikely(block_dump)) {
struct dentry *dentry = NULL;
const char *name = "?";
if (!list_empty(&inode->i_dentry)) {
dentry = list_entry(inode->i_dentry.next,
struct dentry, d_alias);
if (dentry && dentry->d_name.name)
name = (const char *) dentry->d_name.name;
}
if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev"))
printk(KERN_DEBUG
"%s(%d): dirtied inode %lu (%s) on %s\n",
current->comm, task_pid_nr(current), inode->i_ino,
name, inode->i_sb->s_id);
}
spin_lock(&inode_lock);
if ((inode->i_state & flags) != flags) {
const int was_dirty = inode->i_state & I_DIRTY;
inode->i_state |= flags;
/*
* If the inode is being synced, just update its dirty state.
* The unlocker will place the inode on the appropriate
* superblock list, based upon its state.
*/
if (inode->i_state & I_SYNC)
goto out;
/*
* Only add valid (hashed) inodes to the superblock's
* dirty list. Add blockdev inodes as well.
*/
if (!S_ISBLK(inode->i_mode)) {
if (hlist_unhashed(&inode->i_hash))
goto out;
}
if (inode->i_state & (I_FREEING|I_CLEAR))
goto out;
/*
* If the inode was already on s_dirty/s_io/s_more_io, don't
* reposition it (that would break s_dirty time-ordering).
*/
if (!was_dirty) {
inode->dirtied_when = jiffies;
list_move(&inode->i_list, &sb->s_dirty);
}
}
out:
spin_unlock(&inode_lock);
}
EXPORT_SYMBOL(__mark_inode_dirty);
static int write_inode(struct inode *inode, int sync)
{
if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
return inode->i_sb->s_op->write_inode(inode, sync);
return 0;
}
/*
* Redirty an inode: set its when-it-was dirtied timestamp and move it to the
* furthest end of its superblock's dirty-inode list.
*
* Before stamping the inode's ->dirtied_when, we check to see whether it is
* already the most-recently-dirtied inode on the s_dirty list. If that is
* the case then the inode must have been redirtied while it was being written
* out and we don't reset its dirtied_when.
*/
static void redirty_tail(struct inode *inode)
{
struct super_block *sb = inode->i_sb;
if (!list_empty(&sb->s_dirty)) {
struct inode *tail_inode;
tail_inode = list_entry(sb->s_dirty.next, struct inode, i_list);
if (!time_after_eq(inode->dirtied_when,
tail_inode->dirtied_when))
inode->dirtied_when = jiffies;
}
list_move(&inode->i_list, &sb->s_dirty);
}
/*
* requeue inode for re-scanning after sb->s_io list is exhausted.
*/
static void requeue_io(struct inode *inode)
{
list_move(&inode->i_list, &inode->i_sb->s_more_io);
}
static void inode_sync_complete(struct inode *inode)
{
/*
* Prevent speculative execution through spin_unlock(&inode_lock);
*/
smp_mb();
wake_up_bit(&inode->i_state, __I_SYNC);
}
/*
* Move expired dirty inodes from @delaying_queue to @dispatch_queue.
*/
static void move_expired_inodes(struct list_head *delaying_queue,
struct list_head *dispatch_queue,
unsigned long *older_than_this)
{
while (!list_empty(delaying_queue)) {
struct inode *inode = list_entry(delaying_queue->prev,
struct inode, i_list);
if (older_than_this &&
time_after(inode->dirtied_when, *older_than_this))
break;
list_move(&inode->i_list, dispatch_queue);
}
}
/*
* Queue all expired dirty inodes for io, eldest first.
*/
static void queue_io(struct super_block *sb,
unsigned long *older_than_this)
{
list_splice_init(&sb->s_more_io, sb->s_io.prev);
move_expired_inodes(&sb->s_dirty, &sb->s_io, older_than_this);
}
int sb_has_dirty_inodes(struct super_block *sb)
{
return !list_empty(&sb->s_dirty) ||
!list_empty(&sb->s_io) ||
!list_empty(&sb->s_more_io);
}
EXPORT_SYMBOL(sb_has_dirty_inodes);
/*
* Write a single inode's dirty pages and inode data out to disk.
* If `wait' is set, wait on the writeout.
*
* The whole writeout design is quite complex and fragile. We want to avoid
* starvation of particular inodes when others are being redirtied, prevent
* livelocks, etc.
*
* Called under inode_lock.
*/
static int
__sync_single_inode(struct inode *inode, struct writeback_control *wbc)
{
unsigned dirty;
struct address_space *mapping = inode->i_mapping;
int wait = wbc->sync_mode == WB_SYNC_ALL;
int ret;
BUG_ON(inode->i_state & I_SYNC);
/* Set I_SYNC, reset I_DIRTY */
dirty = inode->i_state & I_DIRTY;
inode->i_state |= I_SYNC;
inode->i_state &= ~I_DIRTY;
spin_unlock(&inode_lock);
ret = do_writepages(mapping, wbc);
/* Don't write the inode if only I_DIRTY_PAGES was set */
if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
int err = write_inode(inode, wait);
if (ret == 0)
ret = err;
}
if (wait) {
int err = filemap_fdatawait(mapping);
if (ret == 0)
ret = err;
}
spin_lock(&inode_lock);
inode->i_state &= ~I_SYNC;
if (!(inode->i_state & I_FREEING)) {
if (!(inode->i_state & I_DIRTY) &&
mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
/*
* We didn't write back all the pages. nfs_writepages()
* sometimes bales out without doing anything. Redirty
* the inode; Move it from s_io onto s_more_io/s_dirty.
*/
/*
* akpm: if the caller was the kupdate function we put
* this inode at the head of s_dirty so it gets first
* consideration. Otherwise, move it to the tail, for
* the reasons described there. I'm not really sure
* how much sense this makes. Presumably I had a good
* reasons for doing it this way, and I'd rather not
* muck with it at present.
*/
if (wbc->for_kupdate) {
/*
* For the kupdate function we move the inode
* to s_more_io so it will get more writeout as
* soon as the queue becomes uncongested.
*/
inode->i_state |= I_DIRTY_PAGES;
if (wbc->nr_to_write <= 0) {
/*
* slice used up: queue for next turn
*/
requeue_io(inode);
} else {
/*
* somehow blocked: retry later
*/
redirty_tail(inode);
}
} else {
/*
* Otherwise fully redirty the inode so that
* other inodes on this superblock will get some
* writeout. Otherwise heavy writing to one
* file would indefinitely suspend writeout of
* all the other files.
*/
inode->i_state |= I_DIRTY_PAGES;
redirty_tail(inode);
}
} else if (inode->i_state & I_DIRTY) {
/*
* Someone redirtied the inode while were writing back
* the pages.
*/
redirty_tail(inode);
} else if (atomic_read(&inode->i_count)) {
/*
* The inode is clean, inuse
*/
list_move(&inode->i_list, &inode_in_use);
} else {
/*
* The inode is clean, unused
*/
list_move(&inode->i_list, &inode_unused);
}
}
inode_sync_complete(inode);
return ret;
}
/*
* Write out an inode's dirty pages. Called under inode_lock. Either the
* caller has ref on the inode (either via __iget or via syscall against an fd)
* or the inode has I_WILL_FREE set (via generic_forget_inode)
*/
static int
__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
{
wait_queue_head_t *wqh;
if (!atomic_read(&inode->i_count))
WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
else
WARN_ON(inode->i_state & I_WILL_FREE);
if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_SYNC)) {
/*
* We're skipping this inode because it's locked, and we're not
* doing writeback-for-data-integrity. Move it to s_more_io so
* that writeback can proceed with the other inodes on s_io.
* We'll have another go at writing back this inode when we
* completed a full scan of s_io.
*/
requeue_io(inode);
return 0;
}
/*
* It's a data-integrity sync. We must wait.
*/
if (inode->i_state & I_SYNC) {
DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
do {
spin_unlock(&inode_lock);
__wait_on_bit(wqh, &wq, inode_wait,
TASK_UNINTERRUPTIBLE);
spin_lock(&inode_lock);
} while (inode->i_state & I_SYNC);
}
return __sync_single_inode(inode, wbc);
}
/*
* Write out a superblock's list of dirty inodes. A wait will be performed
* upon no inodes, all inodes or the final one, depending upon sync_mode.
*
* If older_than_this is non-NULL, then only write out inodes which
* had their first dirtying at a time earlier than *older_than_this.
*
* If we're a pdlfush thread, then implement pdflush collision avoidance
* against the entire list.
*
* WB_SYNC_HOLD is a hack for sys_sync(): reattach the inode to sb->s_dirty so
* that it can be located for waiting on in __writeback_single_inode().
*
* If `bdi' is non-zero then we're being asked to writeback a specific queue.
* This function assumes that the blockdev superblock's inodes are backed by
* a variety of queues, so all inodes are searched. For other superblocks,
* assume that all inodes are backed by the same queue.
*
* FIXME: this linear search could get expensive with many fileystems. But
* how to fix? We need to go from an address_space to all inodes which share
* a queue with that address_space. (Easy: have a global "dirty superblocks"
* list).
*
* The inodes to be written are parked on sb->s_io. They are moved back onto
* sb->s_dirty as they are selected for writing. This way, none can be missed
* on the writer throttling path, and we get decent balancing between many
* throttled threads: we don't want them all piling up on inode_sync_wait.
*/
void generic_sync_sb_inodes(struct super_block *sb,
struct writeback_control *wbc)
{
const unsigned long start = jiffies; /* livelock avoidance */
spin_lock(&inode_lock);
if (!wbc->for_kupdate || list_empty(&sb->s_io))
queue_io(sb, wbc->older_than_this);
while (!list_empty(&sb->s_io)) {
struct inode *inode = list_entry(sb->s_io.prev,
struct inode, i_list);
struct address_space *mapping = inode->i_mapping;
struct backing_dev_info *bdi = mapping->backing_dev_info;
long pages_skipped;
if (!bdi_cap_writeback_dirty(bdi)) {
redirty_tail(inode);
if (sb_is_blkdev_sb(sb)) {
/*
* Dirty memory-backed blockdev: the ramdisk
* driver does this. Skip just this inode
*/
continue;
}
/*
* Dirty memory-backed inode against a filesystem other
* than the kernel-internal bdev filesystem. Skip the
* entire superblock.
*/
break;
}
if (wbc->nonblocking && bdi_write_congested(bdi)) {
wbc->encountered_congestion = 1;
if (!sb_is_blkdev_sb(sb))
break; /* Skip a congested fs */
requeue_io(inode);
continue; /* Skip a congested blockdev */
}
if (wbc->bdi && bdi != wbc->bdi) {
if (!sb_is_blkdev_sb(sb))
break; /* fs has the wrong queue */
requeue_io(inode);
continue; /* blockdev has wrong queue */
}
/* Was this inode dirtied after sync_sb_inodes was called? */
if (time_after(inode->dirtied_when, start))
break;
/* Is another pdflush already flushing this queue? */
if (current_is_pdflush() && !writeback_acquire(bdi))
break;
BUG_ON(inode->i_state & I_FREEING);
__iget(inode);
pages_skipped = wbc->pages_skipped;
__writeback_single_inode(inode, wbc);
if (wbc->sync_mode == WB_SYNC_HOLD) {
inode->dirtied_when = jiffies;
list_move(&inode->i_list, &sb->s_dirty);
}
if (current_is_pdflush())
writeback_release(bdi);
if (wbc->pages_skipped != pages_skipped) {
/*
* writeback is not making progress due to locked
* buffers. Skip this inode for now.
*/
redirty_tail(inode);
}
spin_unlock(&inode_lock);
iput(inode);
cond_resched();
spin_lock(&inode_lock);
if (wbc->nr_to_write <= 0) {
wbc->more_io = 1;
break;
}
if (!list_empty(&sb->s_more_io))
wbc->more_io = 1;
}
spin_unlock(&inode_lock);
return; /* Leave any unwritten inodes on s_io */
}
EXPORT_SYMBOL_GPL(generic_sync_sb_inodes);
static void sync_sb_inodes(struct super_block *sb,
struct writeback_control *wbc)
{
generic_sync_sb_inodes(sb, wbc);
}
/*
* Start writeback of dirty pagecache data against all unlocked inodes.
*
* Note:
* We don't need to grab a reference to superblock here. If it has non-empty
* ->s_dirty it's hadn't been killed yet and kill_super() won't proceed
* past sync_inodes_sb() until the ->s_dirty/s_io/s_more_io lists are all
* empty. Since __sync_single_inode() regains inode_lock before it finally moves
* inode from superblock lists we are OK.
*
* If `older_than_this' is non-zero then only flush inodes which have a
* flushtime older than *older_than_this.
*
* If `bdi' is non-zero then we will scan the first inode against each
* superblock until we find the matching ones. One group will be the dirty
* inodes against a filesystem. Then when we hit the dummy blockdev superblock,
* sync_sb_inodes will seekout the blockdev which matches `bdi'. Maybe not
* super-efficient but we're about to do a ton of I/O...
*/
void
writeback_inodes(struct writeback_control *wbc)
{
struct super_block *sb;
might_sleep();
spin_lock(&sb_lock);
restart:
list_for_each_entry_reverse(sb, &super_blocks, s_list) {
if (sb_has_dirty_inodes(sb)) {
/* we're making our own get_super here */
sb->s_count++;
spin_unlock(&sb_lock);
/*
* If we can't get the readlock, there's no sense in
* waiting around, most of the time the FS is going to
* be unmounted by the time it is released.
*/
if (down_read_trylock(&sb->s_umount)) {
if (sb->s_root)
sync_sb_inodes(sb, wbc);
up_read(&sb->s_umount);
}
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto restart;
}
if (wbc->nr_to_write <= 0)
break;
}
spin_unlock(&sb_lock);
}
/*
* writeback and wait upon the filesystem's dirty inodes. The caller will
* do this in two passes - one to write, and one to wait. WB_SYNC_HOLD is
* used to park the written inodes on sb->s_dirty for the wait pass.
*
* A finite limit is set on the number of pages which will be written.
* To prevent infinite livelock of sys_sync().
*
* We add in the number of potentially dirty inodes, because each inode write
* can dirty pagecache in the underlying blockdev.
*/
void sync_inodes_sb(struct super_block *sb, int wait)
{
struct writeback_control wbc = {
.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_HOLD,
.range_start = 0,
.range_end = LLONG_MAX,
};
unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
wbc.nr_to_write = nr_dirty + nr_unstable +
(inodes_stat.nr_inodes - inodes_stat.nr_unused) +
nr_dirty + nr_unstable;
wbc.nr_to_write += wbc.nr_to_write / 2; /* Bit more for luck */
sync_sb_inodes(sb, &wbc);
}
/*
* Rather lame livelock avoidance.
*/
static void set_sb_syncing(int val)
{
struct super_block *sb;
spin_lock(&sb_lock);
list_for_each_entry_reverse(sb, &super_blocks, s_list)
sb->s_syncing = val;
spin_unlock(&sb_lock);
}
/**
* sync_inodes - writes all inodes to disk
* @wait: wait for completion
*
* sync_inodes() goes through each super block's dirty inode list, writes the
* inodes out, waits on the writeout and puts the inodes back on the normal
* list.
*
* This is for sys_sync(). fsync_dev() uses the same algorithm. The subtle
* part of the sync functions is that the blockdev "superblock" is processed
* last. This is because the write_inode() function of a typical fs will
* perform no I/O, but will mark buffers in the blockdev mapping as dirty.
* What we want to do is to perform all that dirtying first, and then write
* back all those inode blocks via the blockdev mapping in one sweep. So the
* additional (somewhat redundant) sync_blockdev() calls here are to make
* sure that really happens. Because if we call sync_inodes_sb(wait=1) with
* outstanding dirty inodes, the writeback goes block-at-a-time within the
* filesystem's write_inode(). This is extremely slow.
*/
static void __sync_inodes(int wait)
{
struct super_block *sb;
spin_lock(&sb_lock);
restart:
list_for_each_entry(sb, &super_blocks, s_list) {
if (sb->s_syncing)
continue;
sb->s_syncing = 1;
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
if (sb->s_root) {
sync_inodes_sb(sb, wait);
sync_blockdev(sb->s_bdev);
}
up_read(&sb->s_umount);
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto restart;
}
spin_unlock(&sb_lock);
}
void sync_inodes(int wait)
{
set_sb_syncing(0);
__sync_inodes(0);
if (wait) {
set_sb_syncing(0);
__sync_inodes(1);
}
}
/**
* write_inode_now - write an inode to disk
* @inode: inode to write to disk
* @sync: whether the write should be synchronous or not
*
* This function commits an inode to disk immediately if it is dirty. This is
* primarily needed by knfsd.
*
* The caller must either have a ref on the inode or must have set I_WILL_FREE.
*/
int write_inode_now(struct inode *inode, int sync)
{
int ret;
struct writeback_control wbc = {
.nr_to_write = LONG_MAX,
.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
.range_start = 0,
.range_end = LLONG_MAX,
};
if (!mapping_cap_writeback_dirty(inode->i_mapping))
wbc.nr_to_write = 0;
might_sleep();
spin_lock(&inode_lock);
ret = __writeback_single_inode(inode, &wbc);
spin_unlock(&inode_lock);
if (sync)
inode_sync_wait(inode);
return ret;
}
EXPORT_SYMBOL(write_inode_now);
/**
* sync_inode - write an inode and its pages to disk.
* @inode: the inode to sync
* @wbc: controls the writeback mode
*
* sync_inode() will write an inode and its pages to disk. It will also
* correctly update the inode on its superblock's dirty inode lists and will
* update inode->i_state.
*
* The caller must have a ref on the inode.
*/
int sync_inode(struct inode *inode, struct writeback_control *wbc)
{
int ret;
spin_lock(&inode_lock);
ret = __writeback_single_inode(inode, wbc);
spin_unlock(&inode_lock);
return ret;
}
EXPORT_SYMBOL(sync_inode);
/**
* generic_osync_inode - flush all dirty data for a given inode to disk
* @inode: inode to write
* @mapping: the address_space that should be flushed
* @what: what to write and wait upon
*
* This can be called by file_write functions for files which have the
* O_SYNC flag set, to flush dirty writes to disk.
*
* @what is a bitmask, specifying which part of the inode's data should be
* written and waited upon.
*
* OSYNC_DATA: i_mapping's dirty data
* OSYNC_METADATA: the buffers at i_mapping->private_list
* OSYNC_INODE: the inode itself
*/
int generic_osync_inode(struct inode *inode, struct address_space *mapping, int what)
{
int err = 0;
int need_write_inode_now = 0;
int err2;
if (what & OSYNC_DATA)
err = filemap_fdatawrite(mapping);
if (what & (OSYNC_METADATA|OSYNC_DATA)) {
err2 = sync_mapping_buffers(mapping);
if (!err)
err = err2;
}
if (what & OSYNC_DATA) {
err2 = filemap_fdatawait(mapping);
if (!err)
err = err2;
}
spin_lock(&inode_lock);
if ((inode->i_state & I_DIRTY) &&
((what & OSYNC_INODE) || (inode->i_state & I_DIRTY_DATASYNC)))
need_write_inode_now = 1;
spin_unlock(&inode_lock);
if (need_write_inode_now) {
err2 = write_inode_now(inode, 1);
if (!err)
err = err2;
}
else
inode_sync_wait(inode);
return err;
}
EXPORT_SYMBOL(generic_osync_inode);