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Subject[PATCH 04/10] afs: Further fix file locking
From
Date
Further fix the file locking in the afs filesystem client in a number of
ways, including:

(1) Don't submit the operation to obtain a lock from the server in a work
queue context, but rather do it in the process context of whoever
issued the requesting system call.

(2) The owner of the file_lock struct at the front of the pending_locks
queue now owns right to talk to the server.

(3) Write locks can be instantly granted if they don't overlap with any
other locks *and* we have a write lock on the server.

(4) In the event of an authentication/permission error, all other matching
pending locks requests are also immediately aborted.

(5) Properly use VFS core locks_lock_file_wait() to distribute the server
lock amongst local client locks, including waiting for the lock to
become available.

Test with:

sqlite3 /afs/.../scratch/billings.sqlite <<EOF
CREATE TABLE hosts (
hostname varchar(80),
shorthost varchar(80),
room varchar(30),
building varchar(30),
PRIMARY KEY(shorthost)
);
EOF

With the version of sqlite3 that I have, this should fail consistently with
EAGAIN, whether or not the program is straced (which introduces some delays
between lock syscalls).

Fixes: 0fafdc9f888b ("afs: Fix file locking")
Reported-by: Jonathan Billings <jsbillin@umich.edu>
Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/afs/flock.c | 388 ++++++++++++++++++++++++++++----------------------------
1 file changed, 194 insertions(+), 194 deletions(-)

diff --git a/fs/afs/flock.c b/fs/afs/flock.c
index 6919f53ed4ad..c022a7bd3d29 100644
--- a/fs/afs/flock.c
+++ b/fs/afs/flock.c
@@ -13,9 +13,11 @@

#define AFS_LOCK_GRANTED 0
#define AFS_LOCK_PENDING 1
+#define AFS_LOCK_YOUR_TRY 2

struct workqueue_struct *afs_lock_manager;

+static void afs_next_locker(struct afs_vnode *vnode, int error);
static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl);
static void afs_fl_release_private(struct file_lock *fl);

@@ -24,6 +26,12 @@ static const struct file_lock_operations afs_lock_ops = {
.fl_release_private = afs_fl_release_private,
};

+static inline void afs_set_lock_state(struct afs_vnode *vnode, enum afs_lock_state state)
+{
+ _debug("STATE %u -> %u", vnode->lock_state, state);
+ vnode->lock_state = state;
+}
+
/*
* if the callback is broken on this vnode, then the lock may now be available
*/
@@ -31,7 +39,13 @@ void afs_lock_may_be_available(struct afs_vnode *vnode)
{
_enter("{%llx:%llu}", vnode->fid.vid, vnode->fid.vnode);

- queue_delayed_work(afs_lock_manager, &vnode->lock_work, 0);
+ if (vnode->lock_state != AFS_VNODE_LOCK_WAITING_FOR_CB)
+ return;
+
+ spin_lock(&vnode->lock);
+ if (vnode->lock_state == AFS_VNODE_LOCK_WAITING_FOR_CB)
+ afs_next_locker(vnode, 0);
+ spin_unlock(&vnode->lock);
}

/*
@@ -75,22 +89,65 @@ void afs_lock_op_done(struct afs_call *call)
* 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)
+static void afs_grant_locks(struct afs_vnode *vnode)
{
struct file_lock *p, *_p;
+ bool exclusive = (vnode->lock_type == AFS_LOCK_WRITE);

- 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);
- }
+ list_for_each_entry_safe(p, _p, &vnode->pending_locks, fl_u.afs.link) {
+ if (!exclusive && p->fl_type == F_WRLCK)
+ continue;
+
+ list_move_tail(&p->fl_u.afs.link, &vnode->granted_locks);
+ p->fl_u.afs.state = AFS_LOCK_GRANTED;
+ wake_up(&p->fl_wait);
+ }
+}
+
+/*
+ * If an error is specified, reject every pending lock that matches the
+ * authentication and type of the lock we failed to get. If there are any
+ * remaining lockers, try to wake up one of them to have a go.
+ */
+static void afs_next_locker(struct afs_vnode *vnode, int error)
+{
+ struct file_lock *p, *_p, *next = NULL;
+ struct key *key = vnode->lock_key;
+ unsigned int fl_type = F_RDLCK;
+
+ _enter("");
+
+ if (vnode->lock_type == AFS_LOCK_WRITE)
+ fl_type = F_WRLCK;
+
+ list_for_each_entry_safe(p, _p, &vnode->pending_locks, fl_u.afs.link) {
+ if (error &&
+ p->fl_type == fl_type &&
+ afs_file_key(p->fl_file) == key) {
+ list_del_init(&p->fl_u.afs.link);
+ p->fl_u.afs.state = error;
+ wake_up(&p->fl_wait);
}
+
+ /* Select the next locker to hand off to. */
+ if (next &&
+ (next->fl_type == F_WRLCK || p->fl_type == F_RDLCK))
+ continue;
+ next = p;
}
+
+ vnode->lock_key = NULL;
+ key_put(key);
+
+ if (next) {
+ afs_set_lock_state(vnode, AFS_VNODE_LOCK_SETTING);
+ next->fl_u.afs.state = AFS_LOCK_YOUR_TRY;
+ wake_up(&next->fl_wait);
+ } else {
+ afs_set_lock_state(vnode, AFS_VNODE_LOCK_NONE);
+ }
+
+ _leave("");
}

/*
@@ -196,8 +253,6 @@ 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, *next;
- afs_lock_type_t type;
struct key *key;
int ret;

@@ -210,7 +265,7 @@ void afs_lock_work(struct work_struct *work)
switch (vnode->lock_state) {
case AFS_VNODE_LOCK_NEED_UNLOCK:
_debug("unlock");
- vnode->lock_state = AFS_VNODE_LOCK_UNLOCKING;
+ afs_set_lock_state(vnode, AFS_VNODE_LOCK_UNLOCKING);
spin_unlock(&vnode->lock);

/* attempt to release the server lock; if it fails, we just
@@ -222,22 +277,9 @@ void afs_lock_work(struct work_struct *work)
vnode->fid.vid, vnode->fid.vnode, ret);

spin_lock(&vnode->lock);
- key_put(vnode->lock_key);
- vnode->lock_key = NULL;
- vnode->lock_state = AFS_VNODE_LOCK_NONE;
-
- if (list_empty(&vnode->pending_locks)) {
- spin_unlock(&vnode->lock);
- return;
- }
-
- /* The new front of the queue now owns the state variables. */
- next = list_entry(vnode->pending_locks.next,
- struct file_lock, fl_u.afs.link);
- vnode->lock_key = key_get(afs_file_key(next->fl_file));
- vnode->lock_type = (next->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;
- vnode->lock_state = AFS_VNODE_LOCK_WAITING_FOR_CB;
- goto again;
+ afs_next_locker(vnode, 0);
+ spin_unlock(&vnode->lock);
+ return;

/* If we've already got a lock, then it must be time to extend that
* lock as AFS locks time out after 5 minutes.
@@ -248,7 +290,7 @@ void afs_lock_work(struct work_struct *work)
ASSERT(!list_empty(&vnode->granted_locks));

key = key_get(vnode->lock_key);
- vnode->lock_state = AFS_VNODE_LOCK_EXTENDING;
+ afs_set_lock_state(vnode, AFS_VNODE_LOCK_EXTENDING);
spin_unlock(&vnode->lock);

ret = afs_extend_lock(vnode, key); /* RPC */
@@ -262,72 +304,26 @@ void afs_lock_work(struct work_struct *work)

if (vnode->lock_state != AFS_VNODE_LOCK_EXTENDING)
goto again;
- vnode->lock_state = AFS_VNODE_LOCK_GRANTED;
+ afs_set_lock_state(vnode, AFS_VNODE_LOCK_GRANTED);

- if (ret == 0)
- afs_schedule_lock_extension(vnode);
- else
+ if (ret != 0)
queue_delayed_work(afs_lock_manager, &vnode->lock_work,
HZ * 10);
spin_unlock(&vnode->lock);
_leave(" [ext]");
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 we're waiting for a callback to indicate lock release, we can't
+ * actually rely on this, so need to recheck at regular intervals. The
+ * problem is that the server might not notify us if the lock just
+ * expires (say because a client died) rather than being explicitly
+ * released.
+ */
case AFS_VNODE_LOCK_WAITING_FOR_CB:
- _debug("get");
-
- key = key_get(vnode->lock_key);
- type = vnode->lock_type;
- vnode->lock_state = AFS_VNODE_LOCK_SETTING;
+ _debug("retry");
+ afs_next_locker(vnode, 0);
spin_unlock(&vnode->lock);
-
- ret = afs_set_lock(vnode, key, type); /* RPC */
- key_put(key);
-
- spin_lock(&vnode->lock);
- switch (ret) {
- case -EWOULDBLOCK:
- _debug("blocked");
- break;
- case 0:
- _debug("acquired");
- vnode->lock_state = AFS_VNODE_LOCK_GRANTED;
- /* Fall through */
- default:
- /* Pass the lock or the error onto the first locker in
- * the list - if they're looking for this type of lock.
- * If they're not, we assume that whoever asked for it
- * took a signal.
- */
- if (list_empty(&vnode->pending_locks)) {
- _debug("withdrawn");
- vnode->lock_state = AFS_VNODE_LOCK_NEED_UNLOCK;
- goto again;
- }
-
- fl = list_entry(vnode->pending_locks.next,
- struct file_lock, fl_u.afs.link);
- type = (fl->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;
- if (vnode->lock_type != type) {
- _debug("changed");
- vnode->lock_state = AFS_VNODE_LOCK_NEED_UNLOCK;
- goto again;
- }
-
- fl->fl_u.afs.state = ret;
- if (ret == 0)
- afs_grant_locks(vnode, fl);
- else
- list_del_init(&fl->fl_u.afs.link);
- wake_up(&fl->fl_wait);
- spin_unlock(&vnode->lock);
- _leave(" [granted]");
- return;
- }
+ return;

default:
/* Looks like a lock request was withdrawn. */
@@ -345,14 +341,15 @@ void afs_lock_work(struct work_struct *work)
*/
static void afs_defer_unlock(struct afs_vnode *vnode)
{
- _enter("");
+ _enter("%u", vnode->lock_state);

- if (vnode->lock_state == AFS_VNODE_LOCK_GRANTED ||
- vnode->lock_state == AFS_VNODE_LOCK_EXTENDING) {
+ if (list_empty(&vnode->granted_locks) &&
+ (vnode->lock_state == AFS_VNODE_LOCK_GRANTED ||
+ vnode->lock_state == AFS_VNODE_LOCK_EXTENDING)) {
cancel_delayed_work(&vnode->lock_work);

- vnode->lock_state = AFS_VNODE_LOCK_NEED_UNLOCK;
- afs_lock_may_be_available(vnode);
+ afs_set_lock_state(vnode, AFS_VNODE_LOCK_NEED_UNLOCK);
+ queue_delayed_work(afs_lock_manager, &vnode->lock_work, 0);
}
}

@@ -401,50 +398,6 @@ static int afs_do_setlk_check(struct afs_vnode *vnode, struct key *key,
return 0;
}

-/*
- * Remove the front runner from the pending queue.
- * - The caller must hold vnode->lock.
- */
-static void afs_dequeue_lock(struct afs_vnode *vnode, struct file_lock *fl)
-{
- struct file_lock *next;
-
- _enter("");
-
- /* ->lock_type, ->lock_key and ->lock_state only belong to this
- * file_lock if we're at the front of the pending queue or if we have
- * the lock granted or if the lock_state is NEED_UNLOCK or UNLOCKING.
- */
- if (vnode->granted_locks.next == &fl->fl_u.afs.link &&
- vnode->granted_locks.prev == &fl->fl_u.afs.link) {
- list_del_init(&fl->fl_u.afs.link);
- afs_defer_unlock(vnode);
- return;
- }
-
- if (!list_empty(&vnode->granted_locks) ||
- vnode->pending_locks.next != &fl->fl_u.afs.link) {
- list_del_init(&fl->fl_u.afs.link);
- return;
- }
-
- list_del_init(&fl->fl_u.afs.link);
- key_put(vnode->lock_key);
- vnode->lock_key = NULL;
- vnode->lock_state = AFS_VNODE_LOCK_NONE;
-
- if (list_empty(&vnode->pending_locks))
- return;
-
- /* The new front of the queue now owns the state variables. */
- next = list_entry(vnode->pending_locks.next,
- struct file_lock, fl_u.afs.link);
- vnode->lock_key = key_get(afs_file_key(next->fl_file));
- vnode->lock_type = (next->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;
- vnode->lock_state = AFS_VNODE_LOCK_WAITING_FOR_CB;
- afs_lock_may_be_available(vnode);
-}
-
/*
* request a lock on a file on the server
*/
@@ -469,44 +422,66 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl)
return ret;

spin_lock(&vnode->lock);
+ list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);

- /* If we've already got a readlock on the server then we instantly
- * grant another readlock, irrespective of whether there are any
- * pending writelocks.
+ /* If we've already got a lock on the server then try to move to having
+ * the VFS grant the requested lock. Note that this means that other
+ * clients may get starved out.
*/
- if (type == AFS_LOCK_READ &&
- vnode->lock_state == AFS_VNODE_LOCK_GRANTED &&
- vnode->lock_type == AFS_LOCK_READ) {
- _debug("instant readlock");
- ASSERT(!list_empty(&vnode->granted_locks));
- goto share_existing_lock;
- }
+ _debug("try %u", vnode->lock_state);
+ if (vnode->lock_state == AFS_VNODE_LOCK_GRANTED) {
+ if (type == AFS_LOCK_READ) {
+ _debug("instant readlock");
+ list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
+ fl->fl_u.afs.state = AFS_LOCK_GRANTED;
+ goto vnode_is_locked_u;
+ }

- list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
+ if (vnode->lock_type == AFS_LOCK_WRITE) {
+ _debug("instant writelock");
+ list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
+ fl->fl_u.afs.state = AFS_LOCK_GRANTED;
+ goto vnode_is_locked_u;
+ }
+ }

if (vnode->lock_state != AFS_VNODE_LOCK_NONE)
goto need_to_wait;

+try_to_lock:
/* We don't have a lock on this vnode and we aren't currently waiting
* for one either, so ask the server for a lock.
*
* Note that we need to be careful if we get interrupted by a signal
* after dispatching the request as we may still get the lock, even
* though we don't wait for the reply (it's not too bad a problem - the
- * lock will expire in 10 mins anyway).
+ * lock will expire in 5 mins anyway).
*/
_debug("not locked");
vnode->lock_key = key_get(key);
vnode->lock_type = type;
- vnode->lock_state = AFS_VNODE_LOCK_SETTING;
+ afs_set_lock_state(vnode, AFS_VNODE_LOCK_SETTING);
spin_unlock(&vnode->lock);

ret = afs_set_lock(vnode, key, type); /* RPC */

spin_lock(&vnode->lock);
switch (ret) {
+ case -EKEYREJECTED:
+ case -EKEYEXPIRED:
+ case -EKEYREVOKED:
+ case -EPERM:
+ case -EACCES:
+ fl->fl_u.afs.state = ret;
+ list_del_init(&fl->fl_u.afs.link);
+ afs_next_locker(vnode, ret);
+ goto error_unlock;
+
default:
- goto abort_attempt;
+ fl->fl_u.afs.state = ret;
+ list_del_init(&fl->fl_u.afs.link);
+ afs_next_locker(vnode, 0);
+ goto error_unlock;

case -EWOULDBLOCK:
/* The server doesn't have a lock-waiting queue, so the client
@@ -516,29 +491,23 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl)
_debug("would block");
ASSERT(list_empty(&vnode->granted_locks));
ASSERTCMP(vnode->pending_locks.next, ==, &fl->fl_u.afs.link);
- vnode->lock_state = AFS_VNODE_LOCK_WAITING_FOR_CB;
- goto need_to_wait;
+ goto lock_is_contended;

case 0:
_debug("acquired");
- break;
+ afs_set_lock_state(vnode, AFS_VNODE_LOCK_GRANTED);
+ afs_grant_locks(vnode);
+ goto vnode_is_locked_u;
}

- /* we've acquired a server lock, but it needs to be renewed after 5
- * mins */
- vnode->lock_state = AFS_VNODE_LOCK_GRANTED;
- afs_schedule_lock_extension(vnode);
-
-share_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 */
+vnode_is_locked_u:
spin_unlock(&vnode->lock);
+vnode_is_locked:
+ /* the lock has been granted by the server... */
+ ASSERTCMP(fl->fl_u.afs.state, ==, AFS_LOCK_GRANTED);

- ret = posix_lock_file(file, fl, NULL);
+ /* ... but the VFS still needs to distribute access on this client. */
+ ret = locks_lock_file_wait(file, fl);
if (ret < 0)
goto vfs_rejected_lock;

@@ -550,38 +519,61 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl)
_leave(" = 0");
return 0;

+lock_is_contended:
+ if (!(fl->fl_flags & FL_SLEEP)) {
+ list_del_init(&fl->fl_u.afs.link);
+ afs_next_locker(vnode, 0);
+ ret = -EAGAIN;
+ goto error_unlock;
+ }
+
+ afs_set_lock_state(vnode, AFS_VNODE_LOCK_WAITING_FOR_CB);
+ queue_delayed_work(afs_lock_manager, &vnode->lock_work, HZ * 5);
+
need_to_wait:
/* We're going to have to wait. Either this client doesn't have a lock
* on the server yet and we need to wait for a callback to occur, or
- * the client does have a lock on the server, but it belongs to some
- * other process(es) and is incompatible with the lock we want.
+ * the client does have a lock on the server, but it's shared and we
+ * need an exclusive lock.
*/
- ret = -EAGAIN;
- if (fl->fl_flags & FL_SLEEP) {
- spin_unlock(&vnode->lock);
+ spin_unlock(&vnode->lock);

- _debug("sleep");
- ret = wait_event_interruptible(fl->fl_wait,
- fl->fl_u.afs.state != AFS_LOCK_PENDING);
+ _debug("sleep");
+ ret = wait_event_interruptible(fl->fl_wait,
+ fl->fl_u.afs.state != AFS_LOCK_PENDING);
+ _debug("wait = %d", ret);

+ if (fl->fl_u.afs.state >= 0 && fl->fl_u.afs.state != AFS_LOCK_GRANTED) {
spin_lock(&vnode->lock);
- }

- if (fl->fl_u.afs.state == AFS_LOCK_GRANTED)
- goto given_lock;
- if (fl->fl_u.afs.state < 0)
- ret = fl->fl_u.afs.state;
+ switch (fl->fl_u.afs.state) {
+ case AFS_LOCK_YOUR_TRY:
+ fl->fl_u.afs.state = AFS_LOCK_PENDING;
+ goto try_to_lock;
+ case AFS_LOCK_PENDING:
+ if (ret > 0) {
+ /* We need to retry the lock. We may not be
+ * notified by the server if it just expired
+ * rather than being released.
+ */
+ ASSERTCMP(vnode->lock_state, ==, AFS_VNODE_LOCK_WAITING_FOR_CB);
+ afs_set_lock_state(vnode, AFS_VNODE_LOCK_SETTING);
+ fl->fl_u.afs.state = AFS_LOCK_PENDING;
+ goto try_to_lock;
+ }
+ goto error_unlock;
+ case AFS_LOCK_GRANTED:
+ default:
+ break;
+ }

-abort_attempt:
- /* we aren't going to get the lock, either because we're unwilling to
- * wait, or because some signal happened */
- _debug("abort");
- afs_dequeue_lock(vnode, fl);
+ spin_unlock(&vnode->lock);
+ }

-error_unlock:
- spin_unlock(&vnode->lock);
- _leave(" = %d", ret);
- return ret;
+ if (fl->fl_u.afs.state == AFS_LOCK_GRANTED)
+ goto vnode_is_locked;
+ ret = fl->fl_u.afs.state;
+ goto error;

vfs_rejected_lock:
/* The VFS rejected the lock we just obtained, so we have to discard
@@ -591,9 +583,13 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl)
_debug("vfs refused %d", ret);
spin_lock(&vnode->lock);
list_del_init(&fl->fl_u.afs.link);
- if (list_empty(&vnode->granted_locks))
- afs_defer_unlock(vnode);
- goto error_unlock;
+ afs_defer_unlock(vnode);
+
+error_unlock:
+ spin_unlock(&vnode->lock);
+error:
+ _leave(" = %d", ret);
+ return ret;
}

/*
@@ -731,7 +727,11 @@ static void afs_fl_release_private(struct file_lock *fl)
_enter("");

spin_lock(&vnode->lock);
- afs_dequeue_lock(vnode, fl);
+
+ list_del_init(&fl->fl_u.afs.link);
+ if (list_empty(&vnode->granted_locks))
+ afs_defer_unlock(vnode);
+
_debug("state %u for %p", vnode->lock_state, vnode);
spin_unlock(&vnode->lock);
}
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