[PATCH 4.19 326/639] afs: Further fix file locking

From: David Howells dhowells@redhat.com

[ Upstream commit 4be5975aea154e164696128d049dec9ed341585c ]

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 Signed-off-by: Sasha Levin sashal@kernel.org --- fs/afs/flock.c | 392 ++++++++++++++++++++++++------------------------- 1 file changed, 196 insertions(+), 196 deletions(-)

diff --git a/fs/afs/flock.c b/fs/afs/flock.c index dffbb456629c9..aea7224ba1981 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 */ @@ -31,14 +39,20 @@ 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); + 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); }

/* * 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) +static void __maybe_unused afs_schedule_lock_extension(struct afs_vnode *vnode) { queue_delayed_work(afs_lock_manager, &vnode->lock_work, AFS_LOCKWAIT * HZ / 2); @@ -49,22 +63,65 @@ static void afs_schedule_lock_extension(struct afs_vnode *vnode) * 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(""); }

/* @@ -170,8 +227,6 @@ 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;

@@ -184,7 +239,7 @@ again: 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 @@ -196,22 +251,9 @@ again: 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. @@ -222,7 +264,7 @@ again: 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 */ @@ -236,72 +278,26 @@ again:

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. */ @@ -319,14 +315,15 @@ again: */ 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); } }

@@ -375,50 +372,6 @@ 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 */ @@ -443,44 +396,66 @@ 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 @@ -490,29 +465,23 @@ 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;

@@ -524,38 +493,61 @@ given_lock: _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 @@ -565,9 +557,13 @@ vfs_rejected_lock: _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; }

/* @@ -583,7 +579,7 @@ static int afs_do_unlk(struct file *file, struct file_lock *fl) /* Flush all pending writes before doing anything with locks. */ vfs_fsync(file, 0);

- ret = posix_lock_file(file, fl, NULL); + ret = locks_lock_file_wait(file, fl); _leave(" = %d [%u]", ret, vnode->lock_state); return ret; } @@ -705,7 +701,11 @@ 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); }