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AFS: fix file locking

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Fix file locking for AFS:

 (*) Start the lock manager thread under a mutex to avoid a race.

 (*) Made the locking non-fair: New readlocks will jump pending writelocks if
     there's a readlock currently granted on a file.  This makes the behaviour
     similar to Linux's VFS locking.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Howells 2007-07-31 00:38:49 -07:00 committed by Linus Torvalds
parent b34bd06e48
commit ff8e210a95
1 changed files with 80 additions and 48 deletions
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78
fs/afs/flock.c
View File

@ -19,6 +19,7 @@ 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 struct file_lock_operations afs_lock_ops = {
.fl_copy_lock = afs_fl_copy_lock,
@ -30,12 +31,20 @@ static struct file_lock_operations afs_lock_ops = {
*/
static int afs_init_lock_manager(void)
{
int ret;
ret = 0;
if (!afs_lock_manager) {
afs_lock_manager = create_singlethread_workqueue("kafs_lockd");
mutex_lock(&afs_lock_manager_mutex);
if (!afs_lock_manager) {
afs_lock_manager =
create_singlethread_workqueue("kafs_lockd");
if (!afs_lock_manager)
return -ENOMEM;
ret = -ENOMEM;
}
return 0;
mutex_unlock(&afs_lock_manager_mutex);
}
return ret;
}
/*
@ -67,6 +76,29 @@ static void afs_schedule_lock_extension(struct afs_vnode *vnode)
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
@ -172,8 +204,7 @@ void afs_lock_work(struct work_struct *work)
struct file_lock, fl_u.afs.link) == fl) {
fl->fl_u.afs.state = ret;
if (ret == AFS_LOCK_GRANTED)
list_move_tail(&fl->fl_u.afs.link,
&vnode->granted_locks);
afs_grant_locks(vnode, fl);
else
list_del_init(&fl->fl_u.afs.link);
wake_up(&fl->fl_wait);
@ -258,10 +289,23 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl)
spin_lock(&vnode->lock);
if (list_empty(&vnode->pending_locks)) {
/* 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->granted_locks)) {
/* 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) |
@ -275,8 +319,10 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl)
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, ==,
@ -290,20 +336,6 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl)
}
}
/* if we've already got a readlock on the server and no waiting
* writelocks, then we might be able to instantly grant another
* readlock */
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;
}
}
/* 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);