flock.c

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/* AFS file locking support
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * 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 afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
    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;

    lock_flocks();

    /* 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:
    unlock_flocks();
    _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->f_dentry->d_inode);

    _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->f_dentry->d_inode);

    _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);
}