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Subject[PATCH] AFS: Fix file locking
Date
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>
---

fs/afs/flock.c | 126 +++++++++++++++++++++++++++++++++++---------------------
1 files changed, 79 insertions(+), 47 deletions(-)

diff --git a/fs/afs/flock.c b/fs/afs/flock.c
index 8f07f8d..bb97105 100644
--- a/fs/afs/flock.c
+++ b/fs/afs/flock.c
@@ -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");
- if (!afs_lock_manager)
- return -ENOMEM;
+ 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 0;
+ return ret;
}

/*
@@ -68,6 +77,29 @@ static void afs_schedule_lock_extension(struct afs_vnode *vnode)
}

/*
+ * 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
@@ -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);
@@ -258,49 +289,50 @@ 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)) {
- _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);
+ /* 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;
+ }

- ret = afs_vnode_set_lock(vnode, key, type);
- clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
- switch (ret) {
- case 0:
- goto acquired_server_lock;
- case -EWOULDBLOCK:
- 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;
- }
- }
+ /* 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);

- /* 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;
+ 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;
}
}

-
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