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Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6

Browse source 
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6:
  fs: simplify iget & friends
  fs: pull inode->i_lock up out of writeback_single_inode
  fs: rename inode_lock to inode_hash_lock
  fs: move i_wb_list out from under inode_lock
  fs: move i_sb_list out from under inode_lock
  fs: remove inode_lock from iput_final and prune_icache
  fs: Lock the inode LRU list separately
  fs: factor inode disposal
  fs: protect inode->i_state with inode->i_lock
  autofs4: Do not potentially dereference NULL pointer returned by fget() in autofs_dev_ioctl_setpipefd()
  autofs4 - remove autofs4_lock
  autofs4 - fix d_manage() return on rcu-walk
  autofs4 - fix autofs4_expire_indirect() traversal
  autofs4 - fix dentry leak in autofs4_expire_direct()
  autofs4 - reinstate last used update on access
  vfs - check non-mountpoint dentry might block in __follow_mount_rcu()
This commit is contained in:
Linus Torvalds 2011-03-24 19:01:30 -07:00
parent 30f5b28e7f 0b2d0724e2
commit d39dd11c3e
27 changed files with 622 additions and 543 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
Documentation/filesystems/Locking
View file

@ -128,7 +128,7 @@ alloc_inode:
destroy_inode:
dirty_inode: (must not sleep)
write_inode:
drop_inode: !!!inode_lock!!!
drop_inode: !!!inode->i_lock!!!
evict_inode:
put_super: write
write_super: read

16
Documentation/filesystems/porting
View file

@ -298,11 +298,14 @@ be used instead. It gets called whenever the inode is evicted, whether it has
remaining links or not. Caller does *not* evict the pagecache or inode-associated
metadata buffers; getting rid of those is responsibility of method, as it had
been for ->delete_inode().
->drop_inode() returns int now; it's called on final iput() with inode_lock
held and it returns true if filesystems wants the inode to be dropped. As before,
generic_drop_inode() is still the default and it's been updated appropriately.
generic_delete_inode() is also alive and it consists simply of return 1. Note that
all actual eviction work is done by caller after ->drop_inode() returns.
->drop_inode() returns int now; it's called on final iput() with
inode->i_lock held and it returns true if filesystems wants the inode to be
dropped. As before, generic_drop_inode() is still the default and it's been
updated appropriately. generic_delete_inode() is also alive and it consists
simply of return 1. Note that all actual eviction work is done by caller after
->drop_inode() returns.
clear_inode() is gone; use end_writeback() instead. As before, it must
be called exactly once on each call of ->evict_inode() (as it used to be for
each call of ->delete_inode()). Unlike before, if you are using inode-associated
@ -395,6 +398,9 @@ Currently you can only have FALLOC_FL_PUNCH_HOLE with FALLOC_FL_KEEP_SIZE set,
so the i_size should not change when hole punching, even when puching the end of
a file off.
--
[mandatory]
--
[mandatory]
->get_sb() is gone. Switch to use of ->mount(). Typically it's just

2
Documentation/filesystems/vfs.txt
View file

@ -254,7 +254,7 @@ or bottom half).
should be synchronous or not, not all filesystems check this flag.
drop_inode: called when the last access to the inode is dropped,
with the inode_lock spinlock held.
with the inode->i_lock spinlock held.
This method should be either NULL (normal UNIX filesystem
semantics) or "generic_delete_inode" (for filesystems that do not

2
fs/autofs4/autofs_i.h
View file

@ -61,8 +61,6 @@ do { \
current->pid, __func__, ##args); \
} while (0)
extern spinlock_t autofs4_lock;
/* Unified info structure. This is pointed to by both the dentry and
inode structures. Each file in the filesystem has an instance of this
structure. It holds a reference to the dentry, so dentries are never

4
fs/autofs4/dev-ioctl.c
View file

@ -372,6 +372,10 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
return -EBUSY;
} else {
struct file *pipe = fget(pipefd);
if (!pipe) {
err = -EBADF;
goto out;
}
if (!pipe->f_op || !pipe->f_op->write) {
err = -EPIPE;
fput(pipe);

84
fs/autofs4/expire.c
View file

@ -86,19 +86,71 @@ static int autofs4_mount_busy(struct vfsmount *mnt, struct dentry *dentry)
return status;
}
/*
* Calculate and dget next entry in the subdirs list under root.
*/
static struct dentry *get_next_positive_subdir(struct dentry *prev,
struct dentry *root)
{
struct autofs_sb_info *sbi = autofs4_sbi(root->d_sb);
struct list_head *next;
struct dentry *p, *q;
spin_lock(&sbi->lookup_lock);
if (prev == NULL) {
spin_lock(&root->d_lock);
prev = dget_dlock(root);
next = prev->d_subdirs.next;
p = prev;
goto start;
}
p = prev;
spin_lock(&p->d_lock);
again:
next = p->d_u.d_child.next;
start:
if (next == &root->d_subdirs) {
spin_unlock(&p->d_lock);
spin_unlock(&sbi->lookup_lock);
dput(prev);
return NULL;
}
q = list_entry(next, struct dentry, d_u.d_child);
spin_lock_nested(&q->d_lock, DENTRY_D_LOCK_NESTED);
/* Negative dentry - try next */
if (!simple_positive(q)) {
spin_unlock(&p->d_lock);
p = q;
goto again;
}
dget_dlock(q);
spin_unlock(&q->d_lock);
spin_unlock(&p->d_lock);
spin_unlock(&sbi->lookup_lock);
dput(prev);
return q;
}
/*
* Calculate and dget next entry in top down tree traversal.
*/
static struct dentry *get_next_positive_dentry(struct dentry *prev,
struct dentry *root)
{
struct autofs_sb_info *sbi = autofs4_sbi(root->d_sb);
struct list_head *next;
struct dentry *p, *ret;
if (prev == NULL)
return dget(root);
spin_lock(&autofs4_lock);
spin_lock(&sbi->lookup_lock);
relock:
p = prev;
spin_lock(&p->d_lock);
@ -110,7 +162,7 @@ static struct dentry *get_next_positive_dentry(struct dentry *prev,
if (p == root) {
spin_unlock(&p->d_lock);
spin_unlock(&autofs4_lock);
spin_unlock(&sbi->lookup_lock);
dput(prev);
return NULL;
}
@ -140,7 +192,7 @@ static struct dentry *get_next_positive_dentry(struct dentry *prev,
dget_dlock(ret);
spin_unlock(&ret->d_lock);
spin_unlock(&p->d_lock);
spin_unlock(&autofs4_lock);
spin_unlock(&sbi->lookup_lock);
dput(prev);
@ -290,11 +342,8 @@ struct dentry *autofs4_expire_direct(struct super_block *sb,
spin_lock(&sbi->fs_lock);
ino = autofs4_dentry_ino(root);
/* No point expiring a pending mount */
if (ino->flags & AUTOFS_INF_PENDING) {
spin_unlock(&sbi->fs_lock);
return NULL;
}
managed_dentry_set_transit(root);
if (ino->flags & AUTOFS_INF_PENDING)
goto out;
if (!autofs4_direct_busy(mnt, root, timeout, do_now)) {
struct autofs_info *ino = autofs4_dentry_ino(root);
ino->flags |= AUTOFS_INF_EXPIRING;
@ -302,7 +351,7 @@ struct dentry *autofs4_expire_direct(struct super_block *sb,
spin_unlock(&sbi->fs_lock);
return root;
}
managed_dentry_clear_transit(root);
out:
spin_unlock(&sbi->fs_lock);
dput(root);
@ -336,13 +385,12 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb,
timeout = sbi->exp_timeout;
dentry = NULL;
while ((dentry = get_next_positive_dentry(dentry, root))) {
while ((dentry = get_next_positive_subdir(dentry, root))) {
spin_lock(&sbi->fs_lock);
ino = autofs4_dentry_ino(dentry);
/* No point expiring a pending mount */
if (ino->flags & AUTOFS_INF_PENDING)
goto cont;
managed_dentry_set_transit(dentry);
goto next;
/*
* Case 1: (i) indirect mount or top level pseudo direct mount
@ -402,8 +450,6 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb,
}
}
next:
managed_dentry_clear_transit(dentry);
cont:
spin_unlock(&sbi->fs_lock);
}
return NULL;
@ -415,13 +461,13 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb,
ino->flags |= AUTOFS_INF_EXPIRING;
init_completion(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);
spin_lock(&autofs4_lock);
spin_lock(&sbi->lookup_lock);
spin_lock(&expired->d_parent->d_lock);
spin_lock_nested(&expired->d_lock, DENTRY_D_LOCK_NESTED);
list_move(&expired->d_parent->d_subdirs, &expired->d_u.d_child);
spin_unlock(&expired->d_lock);
spin_unlock(&expired->d_parent->d_lock);
spin_unlock(&autofs4_lock);
spin_unlock(&sbi->lookup_lock);
return expired;
}
@ -484,8 +530,6 @@ int autofs4_expire_run(struct super_block *sb,
spin_lock(&sbi->fs_lock);
ino = autofs4_dentry_ino(dentry);
ino->flags &= ~AUTOFS_INF_EXPIRING;
if (!d_unhashed(dentry))
managed_dentry_clear_transit(dentry);
complete_all(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);
@ -513,9 +557,7 @@ int autofs4_do_expire_multi(struct super_block *sb, struct vfsmount *mnt,
spin_lock(&sbi->fs_lock);
ino->flags &= ~AUTOFS_INF_EXPIRING;
spin_lock(&dentry->d_lock);
if (ret)
__managed_dentry_clear_transit(dentry);
else {
if (!ret) {
if ((IS_ROOT(dentry) ||
(autofs_type_indirect(sbi->type) &&
IS_ROOT(dentry->d_parent))) &&

62
fs/autofs4/root.c
View file

@ -23,8 +23,6 @@
#include "autofs_i.h"
DEFINE_SPINLOCK(autofs4_lock);
static int autofs4_dir_symlink(struct inode *,struct dentry *,const char *);
static int autofs4_dir_unlink(struct inode *,struct dentry *);
static int autofs4_dir_rmdir(struct inode *,struct dentry *);
@ -125,15 +123,15 @@ static int autofs4_dir_open(struct inode *inode, struct file *file)
* autofs file system so just let the libfs routines handle
* it.
*/
spin_lock(&autofs4_lock);
spin_lock(&sbi->lookup_lock);
spin_lock(&dentry->d_lock);
if (!d_mountpoint(dentry) && list_empty(&dentry->d_subdirs)) {
spin_unlock(&dentry->d_lock);
spin_unlock(&autofs4_lock);
spin_unlock(&sbi->lookup_lock);
return -ENOENT;
}
spin_unlock(&dentry->d_lock);
spin_unlock(&autofs4_lock);
spin_unlock(&sbi->lookup_lock);
out:
return dcache_dir_open(inode, file);
@ -171,7 +169,6 @@ static struct dentry *autofs4_lookup_active(struct dentry *dentry)
const unsigned char *str = name->name;
struct list_head *p, *head;
spin_lock(&autofs4_lock);
spin_lock(&sbi->lookup_lock);
head = &sbi->active_list;
list_for_each(p, head) {
@ -204,14 +201,12 @@ static struct dentry *autofs4_lookup_active(struct dentry *dentry)
dget_dlock(active);
spin_unlock(&active->d_lock);
spin_unlock(&sbi->lookup_lock);
spin_unlock(&autofs4_lock);
return active;
}
next:
spin_unlock(&active->d_lock);
}
spin_unlock(&sbi->lookup_lock);
spin_unlock(&autofs4_lock);
return NULL;
}
@ -226,7 +221,6 @@ static struct dentry *autofs4_lookup_expiring(struct dentry *dentry)
const unsigned char *str = name->name;
struct list_head *p, *head;
spin_lock(&autofs4_lock);
spin_lock(&sbi->lookup_lock);
head = &sbi->expiring_list;
list_for_each(p, head) {
@ -259,14 +253,12 @@ static struct dentry *autofs4_lookup_expiring(struct dentry *dentry)
dget_dlock(expiring);
spin_unlock(&expiring->d_lock);
spin_unlock(&sbi->lookup_lock);
spin_unlock(&autofs4_lock);
return expiring;
}
next:
spin_unlock(&expiring->d_lock);
}
spin_unlock(&sbi->lookup_lock);
spin_unlock(&autofs4_lock);
return NULL;
}
@ -275,17 +267,16 @@ static int autofs4_mount_wait(struct dentry *dentry)
{
struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
struct autofs_info *ino = autofs4_dentry_ino(dentry);
int status;
int status = 0;
if (ino->flags & AUTOFS_INF_PENDING) {
DPRINTK("waiting for mount name=%.*s",
dentry->d_name.len, dentry->d_name.name);
status = autofs4_wait(sbi, dentry, NFY_MOUNT);
DPRINTK("mount wait done status=%d", status);
ino->last_used = jiffies;
return status;
}
return 0;
ino->last_used = jiffies;
return status;
}
static int do_expire_wait(struct dentry *dentry)
@ -319,9 +310,12 @@ static struct dentry *autofs4_mountpoint_changed(struct path *path)
*/
if (autofs_type_indirect(sbi->type) && d_unhashed(dentry)) {
struct dentry *parent = dentry->d_parent;
struct autofs_info *ino;
struct dentry *new = d_lookup(parent, &dentry->d_name);
if (!new)
return NULL;
ino = autofs4_dentry_ino(new);
ino->last_used = jiffies;
dput(path->dentry);
path->dentry = new;
}
@ -338,18 +332,6 @@ static struct vfsmount *autofs4_d_automount(struct path *path)
DPRINTK("dentry=%p %.*s",
dentry, dentry->d_name.len, dentry->d_name.name);
/*
* Someone may have manually umounted this or it was a submount
* that has gone away.
*/
spin_lock(&dentry->d_lock);
if (!d_mountpoint(dentry) && list_empty(&dentry->d_subdirs)) {
if (!(dentry->d_flags & DCACHE_MANAGE_TRANSIT) &&
(dentry->d_flags & DCACHE_NEED_AUTOMOUNT))
__managed_dentry_set_transit(path->dentry);
}
spin_unlock(&dentry->d_lock);
/* The daemon never triggers a mount. */
if (autofs4_oz_mode(sbi))
return NULL;
@ -418,18 +400,17 @@ static struct vfsmount *autofs4_d_automount(struct path *path)
done:
if (!(ino->flags & AUTOFS_INF_EXPIRING)) {
/*
* Any needed mounting has been completed and the path updated
* so turn this into a normal dentry so we don't continually
* call ->d_automount() and ->d_manage().
*/
spin_lock(&dentry->d_lock);
__managed_dentry_clear_transit(dentry);
/*
* Any needed mounting has been completed and the path
* updated so clear DCACHE_NEED_AUTOMOUNT so we don't
* call ->d_automount() on rootless multi-mounts since
* it can lead to an incorrect ELOOP error return.
*
* Only clear DMANAGED_AUTOMOUNT for rootless multi-mounts and
* symlinks as in all other cases the dentry will be covered by
* an actual mount so ->d_automount() won't be called during
* the follow.
*/
spin_lock(&dentry->d_lock);
if ((!d_mountpoint(dentry) &&
!list_empty(&dentry->d_subdirs)) ||
(dentry->d_inode && S_ISLNK(dentry->d_inode->i_mode)))
@ -455,6 +436,8 @@ int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
/* The daemon never waits. */
if (autofs4_oz_mode(sbi)) {
if (rcu_walk)
return 0;
if (!d_mountpoint(dentry))
return -EISDIR;
return 0;
@ -612,12 +595,12 @@ static int autofs4_dir_unlink(struct inode *dir, struct dentry *dentry)
dir->i_mtime = CURRENT_TIME;
spin_lock(&autofs4_lock);
autofs4_add_expiring(dentry);
spin_lock(&sbi->lookup_lock);
__autofs4_add_expiring(dentry);
spin_lock(&dentry->d_lock);
__d_drop(dentry);
spin_unlock(&dentry->d_lock);
spin_unlock(&autofs4_lock);
spin_unlock(&sbi->lookup_lock);
return 0;
}
@ -686,20 +669,17 @@ static int autofs4_dir_rmdir(struct inode *dir, struct dentry *dentry)
if (!autofs4_oz_mode(sbi))
return -EACCES;
spin_lock(&autofs4_lock);
spin_lock(&sbi->lookup_lock);
spin_lock(&dentry->d_lock);
if (!list_empty(&dentry->d_subdirs)) {
spin_unlock(&dentry->d_lock);
spin_unlock(&sbi->lookup_lock);
spin_unlock(&autofs4_lock);
return -ENOTEMPTY;
}
__autofs4_add_expiring(dentry);
spin_unlock(&sbi->lookup_lock);
__d_drop(dentry);
spin_unlock(&dentry->d_lock);
spin_unlock(&autofs4_lock);
spin_unlock(&sbi->lookup_lock);
if (sbi->version < 5)
autofs_clear_leaf_automount_flags(dentry);

6
fs/autofs4/waitq.c
View file

@ -197,12 +197,12 @@ static int autofs4_getpath(struct autofs_sb_info *sbi,
seq = read_seqbegin(&rename_lock);
rcu_read_lock();
spin_lock(&autofs4_lock);
spin_lock(&sbi->fs_lock);
for (tmp = dentry ; tmp != root ; tmp = tmp->d_parent)
len += tmp->d_name.len + 1;
if (!len || --len > NAME_MAX) {
spin_unlock(&autofs4_lock);
spin_unlock(&sbi->fs_lock);
rcu_read_unlock();
if (read_seqretry(&rename_lock, seq))
goto rename_retry;
@ -218,7 +218,7 @@ static int autofs4_getpath(struct autofs_sb_info *sbi,
p -= tmp->d_name.len;
strncpy(p, tmp->d_name.name, tmp->d_name.len);
}
spin_unlock(&autofs4_lock);
spin_unlock(&sbi->fs_lock);
rcu_read_unlock();
if (read_seqretry(&rename_lock, seq))
goto rename_retry;

6
fs/block_dev.c
View file

@ -55,11 +55,13 @@ EXPORT_SYMBOL(I_BDEV);
static void bdev_inode_switch_bdi(struct inode *inode,
struct backing_dev_info *dst)
{
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
spin_lock(&inode->i_lock);
inode->i_data.backing_dev_info = dst;
if (inode->i_state & I_DIRTY)
list_move(&inode->i_wb_list, &dst->wb.b_dirty);
spin_unlock(&inode_lock);
spin_unlock(&inode->i_lock);
spin_unlock(&inode_wb_list_lock);
}
static sector_t max_block(struct block_device *bdev)

2
fs/buffer.c
View file

@ -1138,7 +1138,7 @@ __getblk_slow(struct block_device *bdev, sector_t block, int size)
* inode list.
*
* mark_buffer_dirty() is atomic. It takes bh->b_page->mapping->private_lock,
* mapping->tree_lock and the global inode_lock.
* mapping->tree_lock and mapping->host->i_lock.
*/
void mark_buffer_dirty(struct buffer_head *bh)
{

18
fs/drop_caches.c
View file

@ -8,6 +8,7 @@
#include <linux/writeback.h>
#include <linux/sysctl.h>
#include <linux/gfp.h>
#include "internal.h"
/* A global variable is a bit ugly, but it keeps the code simple */
int sysctl_drop_caches;
@ -16,20 +17,23 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
{
struct inode *inode, *toput_inode = NULL;
spin_lock(&inode_lock);
spin_lock(&inode_sb_list_lock);
list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
continue;
if (inode->i_mapping->nrpages == 0)
spin_lock(&inode->i_lock);
if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
(inode->i_mapping->nrpages == 0)) {
spin_unlock(&inode->i_lock);
continue;
}
__iget(inode);
spin_unlock(&inode_lock);
spin_unlock(&inode->i_lock);
spin_unlock(&inode_sb_list_lock);
invalidate_mapping_pages(inode->i_mapping, 0, -1);
iput(toput_inode);
toput_inode = inode;
spin_lock(&inode_lock);
spin_lock(&inode_sb_list_lock);
}
spin_unlock(&inode_lock);
spin_unlock(&inode_sb_list_lock);
iput(toput_inode);
}

141
fs/fs-writeback.c
View file

@ -175,6 +175,17 @@ void bdi_start_background_writeback(struct backing_dev_info *bdi)
spin_unlock_bh(&bdi->wb_lock);
}
/*
* Remove the inode from the writeback list it is on.
*/
void inode_wb_list_del(struct inode *inode)
{
spin_lock(&inode_wb_list_lock);
list_del_init(&inode->i_wb_list);
spin_unlock(&inode_wb_list_lock);
}
/*
* Redirty an inode: set its when-it-was dirtied timestamp and move it to the
* furthest end of its superblock's dirty-inode list.
@ -188,6 +199,7 @@ static void redirty_tail(struct inode *inode)
{
struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
assert_spin_locked(&inode_wb_list_lock);
if (!list_empty(&wb->b_dirty)) {
struct inode *tail;
@ -205,14 +217,17 @@ static void requeue_io(struct inode *inode)
{
struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
assert_spin_locked(&inode_wb_list_lock);
list_move(&inode->i_wb_list, &wb->b_more_io);
}
static void inode_sync_complete(struct inode *inode)
{
/*
* Prevent speculative execution through spin_unlock(&inode_lock);
* Prevent speculative execution through
* spin_unlock(&inode_wb_list_lock);
*/
smp_mb();
wake_up_bit(&inode->i_state, __I_SYNC);
}
@ -286,6 +301,7 @@ static void move_expired_inodes(struct list_head *delaying_queue,
*/
static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
{
assert_spin_locked(&inode_wb_list_lock);
list_splice_init(&wb->b_more_io, &wb->b_io);
move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
}
@ -306,25 +322,25 @@ static void inode_wait_for_writeback(struct inode *inode)
wait_queue_head_t *wqh;
wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
while (inode->i_state & I_SYNC) {
spin_unlock(&inode_lock);
while (inode->i_state & I_SYNC) {
spin_unlock(&inode->i_lock);
spin_unlock(&inode_wb_list_lock);
__wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
spin_lock(&inode->i_lock);
}
}
/*
* 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)
* Write out an inode's dirty pages. Called under inode_wb_list_lock and
* inode->i_lock. Either the caller has an active reference on the inode or
* the inode has I_WILL_FREE set.
*
* 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
writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
@ -333,6 +349,9 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
unsigned dirty;
int ret;
assert_spin_locked(&inode_wb_list_lock);
assert_spin_locked(&inode->i_lock);
if (!atomic_read(&inode->i_count))
WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
else
@ -363,7 +382,8 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
/* Set I_SYNC, reset I_DIRTY_PAGES */
inode->i_state |= I_SYNC;
inode->i_state &= ~I_DIRTY_PAGES;
spin_unlock(&inode_lock);
spin_unlock(&inode->i_lock);
spin_unlock(&inode_wb_list_lock);
ret = do_writepages(mapping, wbc);
@ -383,10 +403,10 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
* due to delalloc, clear dirty metadata flags right before
* write_inode()
*/
spin_lock(&inode_lock);
spin_lock(&inode->i_lock);
dirty = inode->i_state & I_DIRTY;
inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
spin_unlock(&inode_lock);
spin_unlock(&inode->i_lock);
/* 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, wbc);
@ -394,7 +414,8 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
ret = err;
}
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
spin_lock(&inode->i_lock);
inode->i_state &= ~I_SYNC;
if (!(inode->i_state & I_FREEING)) {
if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
@ -506,7 +527,9 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
* kind does not need peridic writeout yet, and for the latter
* kind writeout is handled by the freer.
*/
spin_lock(&inode->i_lock);
if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
spin_unlock(&inode->i_lock);
requeue_io(inode);
continue;
}
@ -515,10 +538,13 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
* Was this inode dirtied after sync_sb_inodes was called?
* This keeps sync from extra jobs and livelock.
*/
if (inode_dirtied_after(inode, wbc->wb_start))
if (inode_dirtied_after(inode, wbc->wb_start)) {
spin_unlock(&inode->i_lock);
return 1;
}
__iget(inode);
pages_skipped = wbc->pages_skipped;
writeback_single_inode(inode, wbc);
if (wbc->pages_skipped != pages_skipped) {
@ -528,10 +554,11 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
*/
redirty_tail(inode);
}
spin_unlock(&inode_lock);
spin_unlock(&inode->i_lock);
spin_unlock(&inode_wb_list_lock);
iput(inode);
cond_resched();
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
if (wbc->nr_to_write <= 0) {
wbc->more_io = 1;
return 1;
@ -550,7 +577,7 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
if (!wbc->wb_start)
wbc->wb_start = jiffies; /* livelock avoidance */
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
if (!wbc->for_kupdate || list_empty(&wb->b_io))
queue_io(wb, wbc->older_than_this);
@ -568,7 +595,7 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
if (ret)
break;
}
spin_unlock(&inode_lock);
spin_unlock(&inode_wb_list_lock);
/* Leave any unwritten inodes on b_io */
}
@ -577,11 +604,11 @@ static void __writeback_inodes_sb(struct super_block *sb,
{
WARN_ON(!rwsem_is_locked(&sb->s_umount));
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
if (!wbc->for_kupdate || list_empty(&wb->b_io))
queue_io(wb, wbc->older_than_this);
writeback_sb_inodes(sb, wb, wbc, true);
spin_unlock(&inode_lock);
spin_unlock(&inode_wb_list_lock);
}
/*
@ -720,13 +747,15 @@ static long wb_writeback(struct bdi_writeback *wb,
* become available for writeback. Otherwise
* we'll just busyloop.
*/
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
if (!list_empty(&wb->b_more_io)) {
inode = wb_inode(wb->b_more_io.prev);
trace_wbc_writeback_wait(&wbc, wb->bdi);
spin_lock(&inode->i_lock);
inode_wait_for_writeback(inode);
spin_unlock(&inode->i_lock);
}
spin_unlock(&inode_lock);
spin_unlock(&inode_wb_list_lock);
}
return wrote;
@ -992,7 +1021,6 @@ void __mark_inode_dirty(struct inode *inode, int flags)
{
struct super_block *sb = inode->i_sb;
struct backing_dev_info *bdi = NULL;
bool wakeup_bdi = false;
/*
* Don't do this for I_DIRTY_PAGES - that doesn't actually
@ -1016,7 +1044,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
if (unlikely(block_dump))
block_dump___mark_inode_dirty(inode);
spin_lock(&inode_lock);
spin_lock(&inode->i_lock);
if ((inode->i_state & flags) != flags) {
const int was_dirty = inode->i_state & I_DIRTY;
@ -1028,7 +1056,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
* superblock list, based upon its state.
*/
if (inode->i_state & I_SYNC)
goto out;
goto out_unlock_inode;
/*
* Only add valid (hashed) inodes to the superblock's
@ -1036,16 +1064,17 @@ void __mark_inode_dirty(struct inode *inode, int flags)
*/
if (!S_ISBLK(inode->i_mode)) {
if (inode_unhashed(inode))
goto out;
goto out_unlock_inode;
}
if (inode->i_state & I_FREEING)
goto out;
goto out_unlock_inode;
/*
* If the inode was already on b_dirty/b_io/b_more_io, don't
* reposition it (that would break b_dirty time-ordering).
*/
if (!was_dirty) {
bool wakeup_bdi = false;
bdi = inode_to_bdi(inode);
if (bdi_cap_writeback_dirty(bdi)) {
@ -1062,15 +1091,20 @@ void __mark_inode_dirty(struct inode *inode, int flags)
wakeup_bdi = true;
}
spin_unlock(&inode->i_lock);
spin_lock(&inode_wb_list_lock);
inode->dirtied_when = jiffies;
list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
spin_unlock(&inode_wb_list_lock);
if (wakeup_bdi)
bdi_wakeup_thread_delayed(bdi);
return;
}
}
out:
spin_unlock(&inode_lock);
out_unlock_inode:
spin_unlock(&inode->i_lock);
if (wakeup_bdi)
bdi_wakeup_thread_delayed(bdi);
}
EXPORT_SYMBOL(__mark_inode_dirty);
@ -1101,7 +1135,7 @@ static void wait_sb_inodes(struct super_block *sb)
*/
WARN_ON(!rwsem_is_locked(&sb->s_umount));
spin_lock(&inode_lock);
spin_lock(&inode_sb_list_lock);
/*
* Data integrity sync. Must wait for all pages under writeback,
@ -1111,22 +1145,25 @@ static void wait_sb_inodes(struct super_block *sb)
* we still have to wait for that writeout.
*/
list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
struct address_space *mapping;
struct address_space *mapping = inode->i_mapping;
if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
continue;
mapping = inode->i_mapping;
if (mapping->nrpages == 0)
spin_lock(&inode->i_lock);
if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
(mapping->nrpages == 0)) {
spin_unlock(&inode->i_lock);
continue;
}
__iget(inode);
spin_unlock(&inode_lock);
spin_unlock(&inode->i_lock);
spin_unlock(&inode_sb_list_lock);
/*
* We hold a reference to 'inode' so it couldn't have
* been removed from s_inodes list while we dropped the
* inode_lock. We cannot iput the inode now as we can
* be holding the last reference and we cannot iput it
* under inode_lock. So we keep the reference and iput
* it later.
* We hold a reference to 'inode' so it couldn't have been
* removed from s_inodes list while we dropped the
* inode_sb_list_lock. We cannot iput the inode now as we can
* be holding the last reference and we cannot iput it under
* inode_sb_list_lock. So we keep the reference and iput it
* later.
*/
iput(old_inode);
old_inode = inode;
@ -1135,9 +1172,9 @@ static void wait_sb_inodes(struct super_block *sb)
cond_resched();
spin_lock(&inode_lock);
spin_lock(&inode_sb_list_lock);
}
spin_unlock(&inode_lock);
spin_unlock(&inode_sb_list_lock);
iput(old_inode);
}
@ -1271,9 +1308,11 @@ int write_inode_now(struct inode *inode, int sync)
wbc.nr_to_write = 0;
might_sleep();
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
spin_lock(&inode->i_lock);
ret = writeback_single_inode(inode, &wbc);
spin_unlock(&inode_lock);
spin_unlock(&inode->i_lock);
spin_unlock(&inode_wb_list_lock);
if (sync)
inode_sync_wait(inode);
return ret;
@ -1295,9 +1334,11 @@ int sync_inode(struct inode *inode, struct writeback_control *wbc)
{
int ret;
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
spin_lock(&inode->i_lock);
ret = writeback_single_inode(inode, wbc);
spin_unlock(&inode_lock);
spin_unlock(&inode->i_lock);
spin_unlock(&inode_wb_list_lock);
return ret;
}
EXPORT_SYMBOL(sync_inode);

670
fs/inode.c
View file

File diff suppressed because it is too large Load diff

7
fs/internal.h
View file

@ -125,6 +125,13 @@ extern long do_handle_open(int mountdirfd,
/*
* inode.c
*/
extern spinlock_t inode_sb_list_lock;
/*
* fs-writeback.c
*/
extern void inode_wb_list_del(struct inode *inode);
extern int get_nr_dirty_inodes(void);
extern void evict_inodes(struct super_block *);
extern int invalidate_inodes(struct super_block *, bool);

2
fs/logfs/inode.c
View file

@ -293,7 +293,7 @@ static int logfs_write_inode(struct inode *inode, struct writeback_control *wbc)
return ret;
}
/* called with inode_lock held */
/* called with inode->i_lock held */
static int logfs_drop_inode(struct inode *inode)
{
struct logfs_super *super = logfs_super(inode->i_sb);

23
fs/namei.c
View file

@ -992,6 +992,12 @@ int follow_down_one(struct path *path)
return 0;
}
static inline bool managed_dentry_might_block(struct dentry *dentry)
{
return (dentry->d_flags & DCACHE_MANAGE_TRANSIT &&
dentry->d_op->d_manage(dentry, true) < 0);
}
/*
* Skip to top of mountpoint pile in rcuwalk mode. We abort the rcu-walk if we
* meet a managed dentry and we're not walking to "..". True is returned to
@ -1000,19 +1006,26 @@ int follow_down_one(struct path *path)
static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
struct inode **inode, bool reverse_transit)
{
while (d_mountpoint(path->dentry)) {
for (;;) {
struct vfsmount *mounted;
if (unlikely(path->dentry->d_flags & DCACHE_MANAGE_TRANSIT) &&
!reverse_transit &&
path->dentry->d_op->d_manage(path->dentry, true) < 0)
/*
* Don't forget we might have a non-mountpoint managed dentry
* that wants to block transit.
*/
*inode = path->dentry->d_inode;
if (!reverse_transit &&
unlikely(managed_dentry_might_block(path->dentry)))
return false;
if (!d_mountpoint(path->dentry))
break;
mounted = __lookup_mnt(path->mnt, path->dentry, 1);
if (!mounted)
break;
path->mnt = mounted;
path->dentry = mounted->mnt_root;
nd->seq = read_seqcount_begin(&path->dentry->d_seq);
*inode = path->dentry->d_inode;
}
if (unlikely(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT))

42
fs/notify/inode_mark.c
View file

@ -22,13 +22,14 @@
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/spinlock.h>
#include <linux/writeback.h> /* for inode_lock */
#include <asm/atomic.h>
#include <linux/fsnotify_backend.h>
#include "fsnotify.h"
#include "../internal.h"
/*
* Recalculate the mask of events relevant to a given inode locked.
*/
@ -237,15 +238,14 @@ int fsnotify_add_inode_mark(struct fsnotify_mark *mark,
* fsnotify_unmount_inodes - an sb is unmounting. handle any watched inodes.
* @list: list of inodes being unmounted (sb->s_inodes)
*
* Called with inode_lock held, protecting the unmounting super block's list
* of inodes, and with iprune_mutex held, keeping shrink_icache_memory() at bay.
* We temporarily drop inode_lock, however, and CAN block.
* Called during unmount with no locks held, so needs to be safe against
* concurrent modifiers. We temporarily drop inode_sb_list_lock and CAN block.
*/
void fsnotify_unmount_inodes(struct list_head *list)
{
struct inode *inode, *next_i, *need_iput = NULL;
spin_lock(&inode_lock);
spin_lock(&inode_sb_list_lock);
list_for_each_entry_safe(inode, next_i, list, i_sb_list) {
struct inode *need_iput_tmp;
@ -254,8 +254,11 @@ void fsnotify_unmount_inodes(struct list_head *list)
* I_WILL_FREE, or I_NEW which is fine because by that point
* the inode cannot have any associated watches.
*/
if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
spin_lock(&inode->i_lock);
if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
spin_unlock(&inode->i_lock);
continue;
}
/*
* If i_count is zero, the inode cannot have any watches and
@ -263,8 +266,10 @@ void fsnotify_unmount_inodes(struct list_head *list)
* evict all inodes with zero i_count from icache which is
* unnecessarily violent and may in fact be illegal to do.
*/
if (!atomic_read(&inode->i_count))
if (!atomic_read(&inode->i_count)) {
spin_unlock(&inode->i_lock);
continue;
}
need_iput_tmp = need_iput;
need_iput = NULL;
@ -274,22 +279,25 @@ void fsnotify_unmount_inodes(struct list_head *list)
__iget(inode);
else
need_iput_tmp = NULL;
spin_unlock(&inode->i_lock);
/* In case the dropping of a reference would nuke next_i. */
if ((&next_i->i_sb_list != list) &&
atomic_read(&next_i->i_count) &&
!(next_i->i_state & (I_FREEING | I_WILL_FREE))) {
__iget(next_i);
need_iput = next_i;
atomic_read(&next_i->i_count)) {
spin_lock(&next_i->i_lock);
if (!(next_i->i_state & (I_FREEING | I_WILL_FREE))) {
__iget(next_i);
need_iput = next_i;
}
spin_unlock(&next_i->i_lock);
}
/*
* We can safely drop inode_lock here because we hold
* We can safely drop inode_sb_list_lock here because we hold
* references on both inode and next_i. Also no new inodes
* will be added since the umount has begun. Finally,
* iprune_mutex keeps shrink_icache_memory() away.
* will be added since the umount has begun.
*/
spin_unlock(&inode_lock);
spin_unlock(&inode_sb_list_lock);
if (need_iput_tmp)
iput(need_iput_tmp);
@ -301,7 +309,7 @@ void fsnotify_unmount_inodes(struct list_head *list)
iput(inode);
spin_lock(&inode_lock);
spin_lock(&inode_sb_list_lock);
}
spin_unlock(&inode_lock);
spin_unlock(&inode_sb_list_lock);
}

1
fs/notify/mark.c
View file

@ -91,7 +91,6 @@
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/srcu.h>
#include <linux/writeback.h> /* for inode_lock */
#include <asm/atomic.h>

1
fs/notify/vfsmount_mark.c
View file

@ -23,7 +23,6 @@
#include <linux/mount.h>
#include <linux/mutex.h>
#include <linux/spinlock.h>
#include <linux/writeback.h> /* for inode_lock */
#include <asm/atomic.h>

4
fs/ntfs/inode.c
View file

@ -54,7 +54,7 @@
*
* Return 1 if the attributes match and 0 if not.
*
* NOTE: This function runs with the inode_lock spin lock held so it is not
* NOTE: This function runs with the inode->i_lock spin lock held so it is not
* allowed to sleep.
*/
int ntfs_test_inode(struct inode *vi, ntfs_attr *na)
@ -98,7 +98,7 @@ int ntfs_test_inode(struct inode *vi, ntfs_attr *na)
*
* Return 0 on success and -errno on error.
*
* NOTE: This function runs with the inode_lock spin lock held so it is not
* NOTE: This function runs with the inode->i_lock spin lock held so it is not
* allowed to sleep. (Hence the GFP_ATOMIC allocation.)
*/
static int ntfs_init_locked_inode(struct inode *vi, ntfs_attr *na)

41
fs/quota/dquot.c
View file

@ -76,7 +76,7 @@
#include <linux/buffer_head.h>
#include <linux/capability.h>
#include <linux/quotaops.h>
#include <linux/writeback.h> /* for inode_lock, oddly enough.. */
#include "../internal.h" /* ugh */
#include <asm/uaccess.h>
@ -900,33 +900,38 @@ static void add_dquot_ref(struct super_block *sb, int type)
int reserved = 0;
#endif
spin_lock(&inode_lock);
spin_lock(&inode_sb_list_lock);
list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
spin_lock(&inode->i_lock);
if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
!atomic_read(&inode->i_writecount) ||
!dqinit_needed(inode, type)) {
spin_unlock(&inode->i_lock);
continue;
}
#ifdef CONFIG_QUOTA_DEBUG
if (unlikely(inode_get_rsv_space(inode) > 0))
reserved = 1;
#endif
if (!atomic_read(&inode->i_writecount))
continue;
if (!dqinit_needed(inode, type))
continue;
__iget(inode);
spin_unlock(&inode_lock);
spin_unlock(&inode->i_lock);
spin_unlock(&inode_sb_list_lock);
iput(old_inode);
__dquot_initialize(inode, type);
/* We hold a reference to 'inode' so it couldn't have been
* removed from s_inodes list while we dropped the inode_lock.
* We cannot iput the inode now as we can be holding the last
* reference and we cannot iput it under inode_lock. So we
* keep the reference and iput it later. */
/*
* We hold a reference to 'inode' so it couldn't have been
* removed from s_inodes list while we dropped the
* inode_sb_list_lock We cannot iput the inode now as we can be
* holding the last reference and we cannot iput it under
* inode_sb_list_lock. So we keep the reference and iput it
* later.
*/
old_inode = inode;
spin_lock(&inode_lock);
spin_lock(&inode_sb_list_lock);
}
spin_unlock(&inode_lock);
spin_unlock(&inode_sb_list_lock);
iput(old_inode);
#ifdef CONFIG_QUOTA_DEBUG
@ -1007,7 +1012,7 @@ static void remove_dquot_ref(struct super_block *sb, int type,
struct inode *inode;
int reserved = 0;
spin_lock(&inode_lock);
spin_lock(&inode_sb_list_lock);
list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
/*
* We have to scan also I_NEW inodes because they can already
@ -1021,7 +1026,7 @@ static void remove_dquot_ref(struct super_block *sb, int type,
remove_inode_dquot_ref(inode, type, tofree_head);
}
}
spin_unlock(&inode_lock);
spin_unlock(&inode_sb_list_lock);
#ifdef CONFIG_QUOTA_DEBUG
if (reserved) {
printk(KERN_WARNING "VFS (%s): Writes happened after quota"

2
include/linux/fs.h
View file

@ -1636,7 +1636,7 @@ struct super_operations {
};
/*
* Inode state bits. Protected by inode_lock.
* Inode state bits. Protected by inode->i_lock
*
* Three bits determine the dirty state of the inode, I_DIRTY_SYNC,
* I_DIRTY_DATASYNC and I_DIRTY_PAGES.

2
include/linux/quotaops.h
View file

@ -277,7 +277,7 @@ static inline int dquot_alloc_space(struct inode *inode, qsize_t nr)
/*
* Mark inode fully dirty. Since we are allocating blocks, inode
* would become fully dirty soon anyway and it reportedly
* reduces inode_lock contention.
* reduces lock contention.
*/
mark_inode_dirty(inode);
}

2
include/linux/writeback.h
View file

@ -9,7 +9,7 @@
struct backing_dev_info;
extern spinlock_t inode_lock;
extern spinlock_t inode_wb_list_lock;
/*
* fs/fs-writeback.c

8
mm/backing-dev.c
View file

@ -67,14 +67,14 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
struct inode *inode;
nr_wb = nr_dirty = nr_io = nr_more_io = 0;
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
nr_dirty++;
list_for_each_entry(inode, &wb->b_io, i_wb_list)
nr_io++;
list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
nr_more_io++;
spin_unlock(&inode_lock);
spin_unlock(&inode_wb_list_lock);
global_dirty_limits(&background_thresh, &dirty_thresh);
bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
@ -676,11 +676,11 @@ void bdi_destroy(struct backing_dev_info *bdi)
if (bdi_has_dirty_io(bdi)) {
struct bdi_writeback *dst = &default_backing_dev_info.wb;
spin_lock(&inode_lock);
spin_lock(&inode_wb_list_lock);
list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
list_splice(&bdi->wb.b_io, &dst->b_io);
list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
spin_unlock(&inode_lock);
spin_unlock(&inode_wb_list_lock);
}
bdi_unregister(bdi);

10
mm/filemap.c
View file

@ -80,8 +80,8 @@
* ->i_mutex
* ->i_alloc_sem (various)
*
* ->inode_lock
* ->sb_lock (fs/fs-writeback.c)
* inode_wb_list_lock
* sb_lock (fs/fs-writeback.c)
* ->mapping->tree_lock (__sync_single_inode)
*
* ->i_mmap_lock
@ -98,8 +98,10 @@
* ->zone.lru_lock (check_pte_range->isolate_lru_page)
* ->private_lock (page_remove_rmap->set_page_dirty)
* ->tree_lock (page_remove_rmap->set_page_dirty)
* ->inode_lock (page_remove_rmap->set_page_dirty)
* ->inode_lock (zap_pte_range->set_page_dirty)
* inode_wb_list_lock (page_remove_rmap->set_page_dirty)
* ->inode->i_lock (page_remove_rmap->set_page_dirty)
* inode_wb_list_lock (zap_pte_range->set_page_dirty)
* ->inode->i_lock (zap_pte_range->set_page_dirty)
* ->private_lock (zap_pte_range->__set_page_dirty_buffers)
*
* (code doesn't rely on that order, so you could switch it around)

5
mm/rmap.c
View file

@ -31,11 +31,12 @@
* swap_lock (in swap_duplicate, swap_info_get)
* mmlist_lock (in mmput, drain_mmlist and others)
* mapping->private_lock (in __set_page_dirty_buffers)
* inode_lock (in set_page_dirty's __mark_inode_dirty)
* inode->i_lock (in set_page_dirty's __mark_inode_dirty)
* inode_wb_list_lock (in set_page_dirty's __mark_inode_dirty)
* sb_lock (within inode_lock in fs/fs-writeback.c)
* mapping->tree_lock (widely used, in set_page_dirty,
* in arch-dependent flush_dcache_mmap_lock,
* within inode_lock in __sync_single_inode)
* within inode_wb_list_lock in __sync_single_inode)
*
* (code doesn't rely on that order so it could be switched around)
* ->tasklist_lock