linux/fs/afs/flock.c
Jeff Layton 1c8c601a8c locks: protect most of the file_lock handling with i_lock
Having a global lock that protects all of this code is a clear
scalability problem. Instead of doing that, move most of the code to be
protected by the i_lock instead. The exceptions are the global lists
that the ->fl_link sits on, and the ->fl_block list.

->fl_link is what connects these structures to the
global lists, so we must ensure that we hold those locks when iterating
over or updating these lists.

Furthermore, sound deadlock detection requires that we hold the
blocked_list state steady while checking for loops. We also must ensure
that the search and update to the list are atomic.

For the checking and insertion side of the blocked_list, push the
acquisition of the global lock into __posix_lock_file and ensure that
checking and update of the  blocked_list is done without dropping the
lock in between.

On the removal side, when waking up blocked lock waiters, take the
global lock before walking the blocked list and dequeue the waiters from
the global list prior to removal from the fl_block list.

With this, deadlock detection should be race free while we minimize
excessive file_lock_lock thrashing.

Finally, in order to avoid a lock inversion problem when handling
/proc/locks output we must ensure that manipulations of the fl_block
list are also protected by the file_lock_lock.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2013-06-29 12:57:42 +04:00

590 lines
16 KiB
C

/* AFS file locking support
*
* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include "internal.h"
#define AFS_LOCK_GRANTED 0
#define AFS_LOCK_PENDING 1
static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl);
static void afs_fl_release_private(struct file_lock *fl);
static struct workqueue_struct *afs_lock_manager;
static DEFINE_MUTEX(afs_lock_manager_mutex);
static const struct file_lock_operations afs_lock_ops = {
.fl_copy_lock = afs_fl_copy_lock,
.fl_release_private = afs_fl_release_private,
};
/*
* initialise the lock manager thread if it isn't already running
*/
static int afs_init_lock_manager(void)
{
int ret;
ret = 0;
if (!afs_lock_manager) {
mutex_lock(&afs_lock_manager_mutex);
if (!afs_lock_manager) {
afs_lock_manager =
create_singlethread_workqueue("kafs_lockd");
if (!afs_lock_manager)
ret = -ENOMEM;
}
mutex_unlock(&afs_lock_manager_mutex);
}
return ret;
}
/*
* destroy the lock manager thread if it's running
*/
void __exit afs_kill_lock_manager(void)
{
if (afs_lock_manager)
destroy_workqueue(afs_lock_manager);
}
/*
* if the callback is broken on this vnode, then the lock may now be available
*/
void afs_lock_may_be_available(struct afs_vnode *vnode)
{
_enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);
queue_delayed_work(afs_lock_manager, &vnode->lock_work, 0);
}
/*
* the lock will time out in 5 minutes unless we extend it, so schedule
* extension in a bit less than that time
*/
static void afs_schedule_lock_extension(struct afs_vnode *vnode)
{
queue_delayed_work(afs_lock_manager, &vnode->lock_work,
AFS_LOCKWAIT * HZ / 2);
}
/*
* grant one or more locks (readlocks are allowed to jump the queue if the
* first lock in the queue is itself a readlock)
* - the caller must hold the vnode lock
*/
static void afs_grant_locks(struct afs_vnode *vnode, struct file_lock *fl)
{
struct file_lock *p, *_p;
list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
if (fl->fl_type == F_RDLCK) {
list_for_each_entry_safe(p, _p, &vnode->pending_locks,
fl_u.afs.link) {
if (p->fl_type == F_RDLCK) {
p->fl_u.afs.state = AFS_LOCK_GRANTED;
list_move_tail(&p->fl_u.afs.link,
&vnode->granted_locks);
wake_up(&p->fl_wait);
}
}
}
}
/*
* do work for a lock, including:
* - probing for a lock we're waiting on but didn't get immediately
* - extending a lock that's close to timing out
*/
void afs_lock_work(struct work_struct *work)
{
struct afs_vnode *vnode =
container_of(work, struct afs_vnode, lock_work.work);
struct file_lock *fl;
afs_lock_type_t type;
struct key *key;
int ret;
_enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);
spin_lock(&vnode->lock);
if (test_bit(AFS_VNODE_UNLOCKING, &vnode->flags)) {
_debug("unlock");
spin_unlock(&vnode->lock);
/* attempt to release the server lock; if it fails, we just
* wait 5 minutes and it'll time out anyway */
ret = afs_vnode_release_lock(vnode, vnode->unlock_key);
if (ret < 0)
printk(KERN_WARNING "AFS:"
" Failed to release lock on {%x:%x} error %d\n",
vnode->fid.vid, vnode->fid.vnode, ret);
spin_lock(&vnode->lock);
key_put(vnode->unlock_key);
vnode->unlock_key = NULL;
clear_bit(AFS_VNODE_UNLOCKING, &vnode->flags);
}
/* if we've got a lock, then it must be time to extend that lock as AFS
* locks time out after 5 minutes */
if (!list_empty(&vnode->granted_locks)) {
_debug("extend");
if (test_and_set_bit(AFS_VNODE_LOCKING, &vnode->flags))
BUG();
fl = list_entry(vnode->granted_locks.next,
struct file_lock, fl_u.afs.link);
key = key_get(fl->fl_file->private_data);
spin_unlock(&vnode->lock);
ret = afs_vnode_extend_lock(vnode, key);
clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
key_put(key);
switch (ret) {
case 0:
afs_schedule_lock_extension(vnode);
break;
default:
/* ummm... we failed to extend the lock - retry
* extension shortly */
printk(KERN_WARNING "AFS:"
" Failed to extend lock on {%x:%x} error %d\n",
vnode->fid.vid, vnode->fid.vnode, ret);
queue_delayed_work(afs_lock_manager, &vnode->lock_work,
HZ * 10);
break;
}
_leave(" [extend]");
return;
}
/* if we don't have a granted lock, then we must've been called back by
* the server, and so if might be possible to get a lock we're
* currently waiting for */
if (!list_empty(&vnode->pending_locks)) {
_debug("get");
if (test_and_set_bit(AFS_VNODE_LOCKING, &vnode->flags))
BUG();
fl = list_entry(vnode->pending_locks.next,
struct file_lock, fl_u.afs.link);
key = key_get(fl->fl_file->private_data);
type = (fl->fl_type == F_RDLCK) ?
AFS_LOCK_READ : AFS_LOCK_WRITE;
spin_unlock(&vnode->lock);
ret = afs_vnode_set_lock(vnode, key, type);
clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
switch (ret) {
case -EWOULDBLOCK:
_debug("blocked");
break;
case 0:
_debug("acquired");
if (type == AFS_LOCK_READ)
set_bit(AFS_VNODE_READLOCKED, &vnode->flags);
else
set_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
ret = AFS_LOCK_GRANTED;
default:
spin_lock(&vnode->lock);
/* the pending lock may have been withdrawn due to a
* signal */
if (list_entry(vnode->pending_locks.next,
struct file_lock, fl_u.afs.link) == fl) {
fl->fl_u.afs.state = ret;
if (ret == AFS_LOCK_GRANTED)
afs_grant_locks(vnode, fl);
else
list_del_init(&fl->fl_u.afs.link);
wake_up(&fl->fl_wait);
spin_unlock(&vnode->lock);
} else {
_debug("withdrawn");
clear_bit(AFS_VNODE_READLOCKED, &vnode->flags);
clear_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
spin_unlock(&vnode->lock);
afs_vnode_release_lock(vnode, key);
if (!list_empty(&vnode->pending_locks))
afs_lock_may_be_available(vnode);
}
break;
}
key_put(key);
_leave(" [pend]");
return;
}
/* looks like the lock request was withdrawn on a signal */
spin_unlock(&vnode->lock);
_leave(" [no locks]");
}
/*
* pass responsibility for the unlocking of a vnode on the server to the
* manager thread, lest a pending signal in the calling thread interrupt
* AF_RXRPC
* - the caller must hold the vnode lock
*/
static void afs_defer_unlock(struct afs_vnode *vnode, struct key *key)
{
cancel_delayed_work(&vnode->lock_work);
if (!test_and_clear_bit(AFS_VNODE_READLOCKED, &vnode->flags) &&
!test_and_clear_bit(AFS_VNODE_WRITELOCKED, &vnode->flags))
BUG();
if (test_and_set_bit(AFS_VNODE_UNLOCKING, &vnode->flags))
BUG();
vnode->unlock_key = key_get(key);
afs_lock_may_be_available(vnode);
}
/*
* request a lock on a file on the server
*/
static int afs_do_setlk(struct file *file, struct file_lock *fl)
{
struct inode *inode = file_inode(file);
struct afs_vnode *vnode = AFS_FS_I(inode);
afs_lock_type_t type;
struct key *key = file->private_data;
int ret;
_enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);
/* only whole-file locks are supported */
if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
return -EINVAL;
ret = afs_init_lock_manager();
if (ret < 0)
return ret;
fl->fl_ops = &afs_lock_ops;
INIT_LIST_HEAD(&fl->fl_u.afs.link);
fl->fl_u.afs.state = AFS_LOCK_PENDING;
type = (fl->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;
spin_lock(&inode->i_lock);
/* make sure we've got a callback on this file and that our view of the
* data version is up to date */
ret = afs_vnode_fetch_status(vnode, NULL, key);
if (ret < 0)
goto error;
if (vnode->status.lock_count != 0 && !(fl->fl_flags & FL_SLEEP)) {
ret = -EAGAIN;
goto error;
}
spin_lock(&vnode->lock);
/* if we've already got a readlock on the server then we can instantly
* grant another readlock, irrespective of whether there are any
* pending writelocks */
if (type == AFS_LOCK_READ &&
vnode->flags & (1 << AFS_VNODE_READLOCKED)) {
_debug("instant readlock");
ASSERTCMP(vnode->flags &
((1 << AFS_VNODE_LOCKING) |
(1 << AFS_VNODE_WRITELOCKED)), ==, 0);
ASSERT(!list_empty(&vnode->granted_locks));
goto sharing_existing_lock;
}
/* if there's no-one else with a lock on this vnode, then we need to
* ask the server for a lock */
if (list_empty(&vnode->pending_locks) &&
list_empty(&vnode->granted_locks)) {
_debug("not locked");
ASSERTCMP(vnode->flags &
((1 << AFS_VNODE_LOCKING) |
(1 << AFS_VNODE_READLOCKED) |
(1 << AFS_VNODE_WRITELOCKED)), ==, 0);
list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
set_bit(AFS_VNODE_LOCKING, &vnode->flags);
spin_unlock(&vnode->lock);
ret = afs_vnode_set_lock(vnode, key, type);
clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
switch (ret) {
case 0:
_debug("acquired");
goto acquired_server_lock;
case -EWOULDBLOCK:
_debug("would block");
spin_lock(&vnode->lock);
ASSERT(list_empty(&vnode->granted_locks));
ASSERTCMP(vnode->pending_locks.next, ==,
&fl->fl_u.afs.link);
goto wait;
default:
spin_lock(&vnode->lock);
list_del_init(&fl->fl_u.afs.link);
spin_unlock(&vnode->lock);
goto error;
}
}
/* otherwise, we need to wait for a local lock to become available */
_debug("wait local");
list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
wait:
if (!(fl->fl_flags & FL_SLEEP)) {
_debug("noblock");
ret = -EAGAIN;
goto abort_attempt;
}
spin_unlock(&vnode->lock);
/* now we need to sleep and wait for the lock manager thread to get the
* lock from the server */
_debug("sleep");
ret = wait_event_interruptible(fl->fl_wait,
fl->fl_u.afs.state <= AFS_LOCK_GRANTED);
if (fl->fl_u.afs.state <= AFS_LOCK_GRANTED) {
ret = fl->fl_u.afs.state;
if (ret < 0)
goto error;
spin_lock(&vnode->lock);
goto given_lock;
}
/* we were interrupted, but someone may still be in the throes of
* giving us the lock */
_debug("intr");
ASSERTCMP(ret, ==, -ERESTARTSYS);
spin_lock(&vnode->lock);
if (fl->fl_u.afs.state <= AFS_LOCK_GRANTED) {
ret = fl->fl_u.afs.state;
if (ret < 0) {
spin_unlock(&vnode->lock);
goto error;
}
goto given_lock;
}
abort_attempt:
/* we aren't going to get the lock, either because we're unwilling to
* wait, or because some signal happened */
_debug("abort");
if (list_empty(&vnode->granted_locks) &&
vnode->pending_locks.next == &fl->fl_u.afs.link) {
if (vnode->pending_locks.prev != &fl->fl_u.afs.link) {
/* kick the next pending lock into having a go */
list_del_init(&fl->fl_u.afs.link);
afs_lock_may_be_available(vnode);
}
} else {
list_del_init(&fl->fl_u.afs.link);
}
spin_unlock(&vnode->lock);
goto error;
acquired_server_lock:
/* we've acquired a server lock, but it needs to be renewed after 5
* mins */
spin_lock(&vnode->lock);
afs_schedule_lock_extension(vnode);
if (type == AFS_LOCK_READ)
set_bit(AFS_VNODE_READLOCKED, &vnode->flags);
else
set_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
sharing_existing_lock:
/* the lock has been granted as far as we're concerned... */
fl->fl_u.afs.state = AFS_LOCK_GRANTED;
list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
given_lock:
/* ... but we do still need to get the VFS's blessing */
ASSERT(!(vnode->flags & (1 << AFS_VNODE_LOCKING)));
ASSERT((vnode->flags & ((1 << AFS_VNODE_READLOCKED) |
(1 << AFS_VNODE_WRITELOCKED))) != 0);
ret = posix_lock_file(file, fl, NULL);
if (ret < 0)
goto vfs_rejected_lock;
spin_unlock(&vnode->lock);
/* again, make sure we've got a callback on this file and, again, make
* sure that our view of the data version is up to date (we ignore
* errors incurred here and deal with the consequences elsewhere) */
afs_vnode_fetch_status(vnode, NULL, key);
error:
spin_unlock(&inode->i_lock);
_leave(" = %d", ret);
return ret;
vfs_rejected_lock:
/* the VFS rejected the lock we just obtained, so we have to discard
* what we just got */
_debug("vfs refused %d", ret);
list_del_init(&fl->fl_u.afs.link);
if (list_empty(&vnode->granted_locks))
afs_defer_unlock(vnode, key);
goto abort_attempt;
}
/*
* unlock on a file on the server
*/
static int afs_do_unlk(struct file *file, struct file_lock *fl)
{
struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
struct key *key = file->private_data;
int ret;
_enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);
/* only whole-file unlocks are supported */
if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
return -EINVAL;
fl->fl_ops = &afs_lock_ops;
INIT_LIST_HEAD(&fl->fl_u.afs.link);
fl->fl_u.afs.state = AFS_LOCK_PENDING;
spin_lock(&vnode->lock);
ret = posix_lock_file(file, fl, NULL);
if (ret < 0) {
spin_unlock(&vnode->lock);
_leave(" = %d [vfs]", ret);
return ret;
}
/* discard the server lock only if all granted locks are gone */
if (list_empty(&vnode->granted_locks))
afs_defer_unlock(vnode, key);
spin_unlock(&vnode->lock);
_leave(" = 0");
return 0;
}
/*
* return information about a lock we currently hold, if indeed we hold one
*/
static int afs_do_getlk(struct file *file, struct file_lock *fl)
{
struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
struct key *key = file->private_data;
int ret, lock_count;
_enter("");
fl->fl_type = F_UNLCK;
mutex_lock(&vnode->vfs_inode.i_mutex);
/* check local lock records first */
ret = 0;
posix_test_lock(file, fl);
if (fl->fl_type == F_UNLCK) {
/* no local locks; consult the server */
ret = afs_vnode_fetch_status(vnode, NULL, key);
if (ret < 0)
goto error;
lock_count = vnode->status.lock_count;
if (lock_count) {
if (lock_count > 0)
fl->fl_type = F_RDLCK;
else
fl->fl_type = F_WRLCK;
fl->fl_start = 0;
fl->fl_end = OFFSET_MAX;
}
}
error:
mutex_unlock(&vnode->vfs_inode.i_mutex);
_leave(" = %d [%hd]", ret, fl->fl_type);
return ret;
}
/*
* manage POSIX locks on a file
*/
int afs_lock(struct file *file, int cmd, struct file_lock *fl)
{
struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
_enter("{%x:%u},%d,{t=%x,fl=%x,r=%Ld:%Ld}",
vnode->fid.vid, vnode->fid.vnode, cmd,
fl->fl_type, fl->fl_flags,
(long long) fl->fl_start, (long long) fl->fl_end);
/* AFS doesn't support mandatory locks */
if (__mandatory_lock(&vnode->vfs_inode) && fl->fl_type != F_UNLCK)
return -ENOLCK;
if (IS_GETLK(cmd))
return afs_do_getlk(file, fl);
if (fl->fl_type == F_UNLCK)
return afs_do_unlk(file, fl);
return afs_do_setlk(file, fl);
}
/*
* manage FLOCK locks on a file
*/
int afs_flock(struct file *file, int cmd, struct file_lock *fl)
{
struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
_enter("{%x:%u},%d,{t=%x,fl=%x}",
vnode->fid.vid, vnode->fid.vnode, cmd,
fl->fl_type, fl->fl_flags);
/*
* No BSD flocks over NFS allowed.
* Note: we could try to fake a POSIX lock request here by
* using ((u32) filp | 0x80000000) or some such as the pid.
* Not sure whether that would be unique, though, or whether
* that would break in other places.
*/
if (!(fl->fl_flags & FL_FLOCK))
return -ENOLCK;
/* we're simulating flock() locks using posix locks on the server */
fl->fl_owner = (fl_owner_t) file;
fl->fl_start = 0;
fl->fl_end = OFFSET_MAX;
if (fl->fl_type == F_UNLCK)
return afs_do_unlk(file, fl);
return afs_do_setlk(file, fl);
}
/*
* the POSIX lock management core VFS code copies the lock record and adds the
* copy into its own list, so we need to add that copy to the vnode's lock
* queue in the same place as the original (which will be deleted shortly
* after)
*/
static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl)
{
_enter("");
list_add(&new->fl_u.afs.link, &fl->fl_u.afs.link);
}
/*
* need to remove this lock from the vnode queue when it's removed from the
* VFS's list
*/
static void afs_fl_release_private(struct file_lock *fl)
{
_enter("");
list_del_init(&fl->fl_u.afs.link);
}