svclock.c

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/*
 * linux/fs/lockd/svclock.c
 *
 * Handling of server-side locks, mostly of the blocked variety.
 * This is the ugliest part of lockd because we tread on very thin ice.
 * GRANT and CANCEL calls may get stuck, meet in mid-flight, etc.
 * IMNSHO introducing the grant callback into the NLM protocol was one
 * of the worst ideas Sun ever had. Except maybe for the idea of doing
 * NFS file locking at all.
 *
 * I'm trying hard to avoid race conditions by protecting most accesses
 * to a file's list of blocked locks through a semaphore. The global
 * list of blocked locks is not protected in this fashion however.
 * Therefore, some functions (such as the RPC callback for the async grant
 * call) move blocked locks towards the head of the list *while some other
 * process might be traversing it*. This should not be a problem in
 * practice, because this will only cause functions traversing the list
 * to visit some blocks twice.
 *
 * Copyright (C) 1996, Olaf Kirch <[email protected]>
 */

#include <linux/types.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/svc_xprt.h>
#include <linux/lockd/nlm.h>
#include <linux/lockd/lockd.h>
#include <linux/kthread.h>

#define NLMDBG_FACILITY     NLMDBG_SVCLOCK

#ifdef CONFIG_LOCKD_V4
#define nlm_deadlock    nlm4_deadlock
#else
#define nlm_deadlock    nlm_lck_denied
#endif

static void nlmsvc_release_block(struct nlm_block *block);
static void nlmsvc_insert_block(struct nlm_block *block, unsigned long);
static void nlmsvc_remove_block(struct nlm_block *block);

static int nlmsvc_setgrantargs(struct nlm_rqst *call, struct nlm_lock *lock);
static void nlmsvc_freegrantargs(struct nlm_rqst *call);
static const struct rpc_call_ops nlmsvc_grant_ops;

/*
 * The list of blocked locks to retry
 */
static LIST_HEAD(nlm_blocked);
static DEFINE_SPINLOCK(nlm_blocked_lock);

#ifdef LOCKD_DEBUG
static const char *nlmdbg_cookie2a(const struct nlm_cookie *cookie)
{
    /*
     * We can get away with a static buffer because we're only
     * called with BKL held.
     */
    static char buf[2*NLM_MAXCOOKIELEN+1];
    unsigned int i, len = sizeof(buf);
    char *p = buf;

    len--;  /* allow for trailing \0 */
    if (len < 3)
        return "???";
    for (i = 0 ; i < cookie->len ; i++) {
        if (len < 2) {
            strcpy(p-3, "...");
            break;
        }
        sprintf(p, "%02x", cookie->data[i]);
        p += 2;
        len -= 2;
    }
    *p = '\0';

    return buf;
}
#endif

/*
 * Insert a blocked lock into the global list
 */
static void
nlmsvc_insert_block_locked(struct nlm_block *block, unsigned long when)
{
    struct nlm_block *b;
    struct list_head *pos;

    dprintk("lockd: nlmsvc_insert_block(%p, %ld)\n", block, when);
    if (list_empty(&block->b_list)) {
        kref_get(&block->b_count);
    } else {
        list_del_init(&block->b_list);
    }

    pos = &nlm_blocked;
    if (when != NLM_NEVER) {
        if ((when += jiffies) == NLM_NEVER)
            when ++;
        list_for_each(pos, &nlm_blocked) {
            b = list_entry(pos, struct nlm_block, b_list);
            if (time_after(b->b_when,when) || b->b_when == NLM_NEVER)
                break;
        }
        /* On normal exit from the loop, pos == &nlm_blocked,
         * so we will be adding to the end of the list - good
         */
    }

    list_add_tail(&block->b_list, pos);
    block->b_when = when;
}

static void nlmsvc_insert_block(struct nlm_block *block, unsigned long when)
{
    spin_lock(&nlm_blocked_lock);
    nlmsvc_insert_block_locked(block, when);
    spin_unlock(&nlm_blocked_lock);
}

/*
 * Remove a block from the global list
 */
static inline void
nlmsvc_remove_block(struct nlm_block *block)
{
    if (!list_empty(&block->b_list)) {
        spin_lock(&nlm_blocked_lock);
        list_del_init(&block->b_list);
        spin_unlock(&nlm_blocked_lock);
        nlmsvc_release_block(block);
    }
}

/*
 * Find a block for a given lock
 */
static struct nlm_block *
nlmsvc_lookup_block(struct nlm_file *file, struct nlm_lock *lock)
{
    struct nlm_block    *block;
    struct file_lock    *fl;

    dprintk("lockd: nlmsvc_lookup_block f=%p pd=%d %Ld-%Ld ty=%d\n",
                file, lock->fl.fl_pid,
                (long long)lock->fl.fl_start,
                (long long)lock->fl.fl_end, lock->fl.fl_type);
    list_for_each_entry(block, &nlm_blocked, b_list) {
        fl = &block->b_call->a_args.lock.fl;
        dprintk("lockd: check f=%p pd=%d %Ld-%Ld ty=%d cookie=%s\n",
                block->b_file, fl->fl_pid,
                (long long)fl->fl_start,
                (long long)fl->fl_end, fl->fl_type,
                nlmdbg_cookie2a(&block->b_call->a_args.cookie));
        if (block->b_file == file && nlm_compare_locks(fl, &lock->fl)) {
            kref_get(&block->b_count);
            return block;
        }
    }

    return NULL;
}

static inline int nlm_cookie_match(struct nlm_cookie *a, struct nlm_cookie *b)
{
    if (a->len != b->len)
        return 0;
    if (memcmp(a->data, b->data, a->len))
        return 0;
    return 1;
}

/*
 * Find a block with a given NLM cookie.
 */
static inline struct nlm_block *
nlmsvc_find_block(struct nlm_cookie *cookie)
{
    struct nlm_block *block;

    list_for_each_entry(block, &nlm_blocked, b_list) {
        if (nlm_cookie_match(&block->b_call->a_args.cookie,cookie))
            goto found;
    }

    return NULL;

found:
    dprintk("nlmsvc_find_block(%s): block=%p\n", nlmdbg_cookie2a(cookie), block);
    kref_get(&block->b_count);
    return block;
}

/*
 * Create a block and initialize it.
 *
 * Note: we explicitly set the cookie of the grant reply to that of
 * the blocked lock request. The spec explicitly mentions that the client
 * should _not_ rely on the callback containing the same cookie as the
 * request, but (as I found out later) that's because some implementations
 * do just this. Never mind the standards comittees, they support our
 * logging industries.
 *
 * 10 years later: I hope we can safely ignore these old and broken
 * clients by now. Let's fix this so we can uniquely identify an incoming
 * GRANTED_RES message by cookie, without having to rely on the client's IP
 * address. --okir
 */
static struct nlm_block *
nlmsvc_create_block(struct svc_rqst *rqstp, struct nlm_host *host,
            struct nlm_file *file, struct nlm_lock *lock,
            struct nlm_cookie *cookie)
{
    struct nlm_block    *block;
    struct nlm_rqst     *call = NULL;

    call = nlm_alloc_call(host);
    if (call == NULL)
        return NULL;

    /* Allocate memory for block, and initialize arguments */
    block = kzalloc(sizeof(*block), GFP_KERNEL);
    if (block == NULL)
        goto failed;
    kref_init(&block->b_count);
    INIT_LIST_HEAD(&block->b_list);
    INIT_LIST_HEAD(&block->b_flist);

    if (!nlmsvc_setgrantargs(call, lock))
        goto failed_free;

    /* Set notifier function for VFS, and init args */
    call->a_args.lock.fl.fl_flags |= FL_SLEEP;
    call->a_args.lock.fl.fl_lmops = &nlmsvc_lock_operations;
    nlmclnt_next_cookie(&call->a_args.cookie);

    dprintk("lockd: created block %p...\n", block);

    /* Create and initialize the block */
    block->b_daemon = rqstp->rq_server;
    block->b_host   = host;
    block->b_file   = file;
    block->b_fl = NULL;
    file->f_count++;

    /* Add to file's list of blocks */
    list_add(&block->b_flist, &file->f_blocks);

    /* Set up RPC arguments for callback */
    block->b_call = call;
    call->a_flags   = RPC_TASK_ASYNC;
    call->a_block = block;

    return block;

failed_free:
    kfree(block);
failed:
    nlmsvc_release_call(call);
    return NULL;
}

/*
 * Delete a block.
 * It is the caller's responsibility to check whether the file
 * can be closed hereafter.
 */
static int nlmsvc_unlink_block(struct nlm_block *block)
{
    int status;
    dprintk("lockd: unlinking block %p...\n", block);

    /* Remove block from list */
    status = posix_unblock_lock(block->b_file->f_file, &block->b_call->a_args.lock.fl);
    nlmsvc_remove_block(block);
    return status;
}

static void nlmsvc_free_block(struct kref *kref)
{
    struct nlm_block *block = container_of(kref, struct nlm_block, b_count);
    struct nlm_file     *file = block->b_file;

    dprintk("lockd: freeing block %p...\n", block);

    /* Remove block from file's list of blocks */
    list_del_init(&block->b_flist);
    mutex_unlock(&file->f_mutex);

    nlmsvc_freegrantargs(block->b_call);
    nlmsvc_release_call(block->b_call);
    nlm_release_file(block->b_file);
    kfree(block->b_fl);
    kfree(block);
}

static void nlmsvc_release_block(struct nlm_block *block)
{
    if (block != NULL)
        kref_put_mutex(&block->b_count, nlmsvc_free_block, &block->b_file->f_mutex);
}

/*
 * Loop over all blocks and delete blocks held by
 * a matching host.
 */
void nlmsvc_traverse_blocks(struct nlm_host *host,
            struct nlm_file *file,
            nlm_host_match_fn_t match)
{
    struct nlm_block *block, *next;

restart:
    mutex_lock(&file->f_mutex);
    list_for_each_entry_safe(block, next, &file->f_blocks, b_flist) {
        if (!match(block->b_host, host))
            continue;
        /* Do not destroy blocks that are not on
         * the global retry list - why? */
        if (list_empty(&block->b_list))
            continue;
        kref_get(&block->b_count);
        mutex_unlock(&file->f_mutex);
        nlmsvc_unlink_block(block);
        nlmsvc_release_block(block);
        goto restart;
    }
    mutex_unlock(&file->f_mutex);
}

/*
 * Initialize arguments for GRANTED call. The nlm_rqst structure
 * has been cleared already.
 */
static int nlmsvc_setgrantargs(struct nlm_rqst *call, struct nlm_lock *lock)
{
    locks_copy_lock(&call->a_args.lock.fl, &lock->fl);
    memcpy(&call->a_args.lock.fh, &lock->fh, sizeof(call->a_args.lock.fh));
    call->a_args.lock.caller = utsname()->nodename;
    call->a_args.lock.oh.len = lock->oh.len;

    /* set default data area */
    call->a_args.lock.oh.data = call->a_owner;
    call->a_args.lock.svid = lock->fl.fl_pid;

    if (lock->oh.len > NLMCLNT_OHSIZE) {
        void *data = kmalloc(lock->oh.len, GFP_KERNEL);
        if (!data)
            return 0;
        call->a_args.lock.oh.data = (u8 *) data;
    }

    memcpy(call->a_args.lock.oh.data, lock->oh.data, lock->oh.len);
    return 1;
}

static void nlmsvc_freegrantargs(struct nlm_rqst *call)
{
    if (call->a_args.lock.oh.data != call->a_owner)
        kfree(call->a_args.lock.oh.data);

    locks_release_private(&call->a_args.lock.fl);
}

/*
 * Deferred lock request handling for non-blocking lock
 */
static __be32
nlmsvc_defer_lock_rqst(struct svc_rqst *rqstp, struct nlm_block *block)
{
    __be32 status = nlm_lck_denied_nolocks;

    block->b_flags |= B_QUEUED;

    nlmsvc_insert_block(block, NLM_TIMEOUT);

    block->b_cache_req = &rqstp->rq_chandle;
    if (rqstp->rq_chandle.defer) {
        block->b_deferred_req =
            rqstp->rq_chandle.defer(block->b_cache_req);
        if (block->b_deferred_req != NULL)
            status = nlm_drop_reply;
    }
    dprintk("lockd: nlmsvc_defer_lock_rqst block %p flags %d status %d\n",
        block, block->b_flags, ntohl(status));

    return status;
}

/*
 * Attempt to establish a lock, and if it can't be granted, block it
 * if required.
 */
__be32
nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
        struct nlm_host *host, struct nlm_lock *lock, int wait,
        struct nlm_cookie *cookie, int reclaim)
{
    struct nlm_block    *block = NULL;
    int         error;
    __be32          ret;

    dprintk("lockd: nlmsvc_lock(%s/%ld, ty=%d, pi=%d, %Ld-%Ld, bl=%d)\n",
                file->f_file->f_path.dentry->d_inode->i_sb->s_id,
                file->f_file->f_path.dentry->d_inode->i_ino,
                lock->fl.fl_type, lock->fl.fl_pid,
                (long long)lock->fl.fl_start,
                (long long)lock->fl.fl_end,
                wait);

    /* Lock file against concurrent access */
    mutex_lock(&file->f_mutex);
    /* Get existing block (in case client is busy-waiting)
     * or create new block
     */
    block = nlmsvc_lookup_block(file, lock);
    if (block == NULL) {
        block = nlmsvc_create_block(rqstp, host, file, lock, cookie);
        ret = nlm_lck_denied_nolocks;
        if (block == NULL)
            goto out;
        lock = &block->b_call->a_args.lock;
    } else
        lock->fl.fl_flags &= ~FL_SLEEP;

    if (block->b_flags & B_QUEUED) {
        dprintk("lockd: nlmsvc_lock deferred block %p flags %d\n",
                            block, block->b_flags);
        if (block->b_granted) {
            nlmsvc_unlink_block(block);
            ret = nlm_granted;
            goto out;
        }
        if (block->b_flags & B_TIMED_OUT) {
            nlmsvc_unlink_block(block);
            ret = nlm_lck_denied;
            goto out;
        }
        ret = nlm_drop_reply;
        goto out;
    }

    if (locks_in_grace(SVC_NET(rqstp)) && !reclaim) {
        ret = nlm_lck_denied_grace_period;
        goto out;
    }
    if (reclaim && !locks_in_grace(SVC_NET(rqstp))) {
        ret = nlm_lck_denied_grace_period;
        goto out;
    }

    if (!wait)
        lock->fl.fl_flags &= ~FL_SLEEP;
    error = vfs_lock_file(file->f_file, F_SETLK, &lock->fl, NULL);
    lock->fl.fl_flags &= ~FL_SLEEP;

    dprintk("lockd: vfs_lock_file returned %d\n", error);
    switch (error) {
        case 0:
            ret = nlm_granted;
            goto out;
        case -EAGAIN:
            /*
             * If this is a blocking request for an
             * already pending lock request then we need
             * to put it back on lockd's block list
             */
            if (wait)
                break;
            ret = nlm_lck_denied;
            goto out;
        case FILE_LOCK_DEFERRED:
            if (wait)
                break;
            /* Filesystem lock operation is in progress
               Add it to the queue waiting for callback */
            ret = nlmsvc_defer_lock_rqst(rqstp, block);
            goto out;
        case -EDEADLK:
            ret = nlm_deadlock;
            goto out;
        default:            /* includes ENOLCK */
            ret = nlm_lck_denied_nolocks;
            goto out;
    }

    ret = nlm_lck_blocked;

    /* Append to list of blocked */
    nlmsvc_insert_block(block, NLM_NEVER);
out:
    mutex_unlock(&file->f_mutex);
    nlmsvc_release_block(block);
    dprintk("lockd: nlmsvc_lock returned %u\n", ret);
    return ret;
}

/*
 * Test for presence of a conflicting lock.
 */
__be32
nlmsvc_testlock(struct svc_rqst *rqstp, struct nlm_file *file,
        struct nlm_host *host, struct nlm_lock *lock,
        struct nlm_lock *conflock, struct nlm_cookie *cookie)
{
    struct nlm_block    *block = NULL;
    int         error;
    __be32          ret;

    dprintk("lockd: nlmsvc_testlock(%s/%ld, ty=%d, %Ld-%Ld)\n",
                file->f_file->f_path.dentry->d_inode->i_sb->s_id,
                file->f_file->f_path.dentry->d_inode->i_ino,
                lock->fl.fl_type,
                (long long)lock->fl.fl_start,
                (long long)lock->fl.fl_end);

    /* Get existing block (in case client is busy-waiting) */
    block = nlmsvc_lookup_block(file, lock);

    if (block == NULL) {
        struct file_lock *conf = kzalloc(sizeof(*conf), GFP_KERNEL);

        if (conf == NULL)
            return nlm_granted;
        block = nlmsvc_create_block(rqstp, host, file, lock, cookie);
        if (block == NULL) {
            kfree(conf);
            return nlm_granted;
        }
        block->b_fl = conf;
    }
    if (block->b_flags & B_QUEUED) {
        dprintk("lockd: nlmsvc_testlock deferred block %p flags %d fl %p\n",
            block, block->b_flags, block->b_fl);
        if (block->b_flags & B_TIMED_OUT) {
            nlmsvc_unlink_block(block);
            ret = nlm_lck_denied;
            goto out;
        }
        if (block->b_flags & B_GOT_CALLBACK) {
            nlmsvc_unlink_block(block);
            if (block->b_fl != NULL
                    && block->b_fl->fl_type != F_UNLCK) {
                lock->fl = *block->b_fl;
                goto conf_lock;
            } else {
                ret = nlm_granted;
                goto out;
            }
        }
        ret = nlm_drop_reply;
        goto out;
    }

    if (locks_in_grace(SVC_NET(rqstp))) {
        ret = nlm_lck_denied_grace_period;
        goto out;
    }
    error = vfs_test_lock(file->f_file, &lock->fl);
    if (error == FILE_LOCK_DEFERRED) {
        ret = nlmsvc_defer_lock_rqst(rqstp, block);
        goto out;
    }
    if (error) {
        ret = nlm_lck_denied_nolocks;
        goto out;
    }
    if (lock->fl.fl_type == F_UNLCK) {
        ret = nlm_granted;
        goto out;
    }

conf_lock:
    dprintk("lockd: conflicting lock(ty=%d, %Ld-%Ld)\n",
        lock->fl.fl_type, (long long)lock->fl.fl_start,
        (long long)lock->fl.fl_end);
    conflock->caller = "somehost";  /* FIXME */
    conflock->len = strlen(conflock->caller);
    conflock->oh.len = 0;       /* don't return OH info */
    conflock->svid = lock->fl.fl_pid;
    conflock->fl.fl_type = lock->fl.fl_type;
    conflock->fl.fl_start = lock->fl.fl_start;
    conflock->fl.fl_end = lock->fl.fl_end;
    ret = nlm_lck_denied;
out:
    if (block)
        nlmsvc_release_block(block);
    return ret;
}

/*
 * Remove a lock.
 * This implies a CANCEL call: We send a GRANT_MSG, the client replies
 * with a GRANT_RES call which gets lost, and calls UNLOCK immediately
 * afterwards. In this case the block will still be there, and hence
 * must be removed.
 */
__be32
nlmsvc_unlock(struct net *net, struct nlm_file *file, struct nlm_lock *lock)
{
    int error;

    dprintk("lockd: nlmsvc_unlock(%s/%ld, pi=%d, %Ld-%Ld)\n",
                file->f_file->f_path.dentry->d_inode->i_sb->s_id,
                file->f_file->f_path.dentry->d_inode->i_ino,
                lock->fl.fl_pid,
                (long long)lock->fl.fl_start,
                (long long)lock->fl.fl_end);

    /* First, cancel any lock that might be there */
    nlmsvc_cancel_blocked(net, file, lock);

    lock->fl.fl_type = F_UNLCK;
    error = vfs_lock_file(file->f_file, F_SETLK, &lock->fl, NULL);

    return (error < 0)? nlm_lck_denied_nolocks : nlm_granted;
}

/*
 * Cancel a previously blocked request.
 *
 * A cancel request always overrides any grant that may currently
 * be in progress.
 * The calling procedure must check whether the file can be closed.
 */
__be32
nlmsvc_cancel_blocked(struct net *net, struct nlm_file *file, struct nlm_lock *lock)
{
    struct nlm_block    *block;
    int status = 0;

    dprintk("lockd: nlmsvc_cancel(%s/%ld, pi=%d, %Ld-%Ld)\n",
                file->f_file->f_path.dentry->d_inode->i_sb->s_id,
                file->f_file->f_path.dentry->d_inode->i_ino,
                lock->fl.fl_pid,
                (long long)lock->fl.fl_start,
                (long long)lock->fl.fl_end);

    if (locks_in_grace(net))
        return nlm_lck_denied_grace_period;

    mutex_lock(&file->f_mutex);
    block = nlmsvc_lookup_block(file, lock);
    mutex_unlock(&file->f_mutex);
    if (block != NULL) {
        vfs_cancel_lock(block->b_file->f_file,
                &block->b_call->a_args.lock.fl);
        status = nlmsvc_unlink_block(block);
        nlmsvc_release_block(block);
    }
    return status ? nlm_lck_denied : nlm_granted;
}

/*
 * This is a callback from the filesystem for VFS file lock requests.
 * It will be used if lm_grant is defined and the filesystem can not
 * respond to the request immediately.
 * For GETLK request it will copy the reply to the nlm_block.
 * For SETLK or SETLKW request it will get the local posix lock.
 * In all cases it will move the block to the head of nlm_blocked q where
 * nlmsvc_retry_blocked() can send back a reply for SETLKW or revisit the
 * deferred rpc for GETLK and SETLK.
 */
static void
nlmsvc_update_deferred_block(struct nlm_block *block, struct file_lock *conf,
                 int result)
{
    block->b_flags |= B_GOT_CALLBACK;
    if (result == 0)
        block->b_granted = 1;
    else
        block->b_flags |= B_TIMED_OUT;
    if (conf) {
        if (block->b_fl)
            __locks_copy_lock(block->b_fl, conf);
    }
}

static int nlmsvc_grant_deferred(struct file_lock *fl, struct file_lock *conf,
                    int result)
{
    struct nlm_block *block;
    int rc = -ENOENT;

    spin_lock(&nlm_blocked_lock);
    list_for_each_entry(block, &nlm_blocked, b_list) {
        if (nlm_compare_locks(&block->b_call->a_args.lock.fl, fl)) {
            dprintk("lockd: nlmsvc_notify_blocked block %p flags %d\n",
                            block, block->b_flags);
            if (block->b_flags & B_QUEUED) {
                if (block->b_flags & B_TIMED_OUT) {
                    rc = -ENOLCK;
                    break;
                }
                nlmsvc_update_deferred_block(block, conf, result);
            } else if (result == 0)
                block->b_granted = 1;

            nlmsvc_insert_block_locked(block, 0);
            svc_wake_up(block->b_daemon);
            rc = 0;
            break;
        }
    }
    spin_unlock(&nlm_blocked_lock);
    if (rc == -ENOENT)
        printk(KERN_WARNING "lockd: grant for unknown block\n");
    return rc;
}

/*
 * Unblock a blocked lock request. This is a callback invoked from the
 * VFS layer when a lock on which we blocked is removed.
 *
 * This function doesn't grant the blocked lock instantly, but rather moves
 * the block to the head of nlm_blocked where it can be picked up by lockd.
 */
static void
nlmsvc_notify_blocked(struct file_lock *fl)
{
    struct nlm_block    *block;

    dprintk("lockd: VFS unblock notification for block %p\n", fl);
    spin_lock(&nlm_blocked_lock);
    list_for_each_entry(block, &nlm_blocked, b_list) {
        if (nlm_compare_locks(&block->b_call->a_args.lock.fl, fl)) {
            nlmsvc_insert_block_locked(block, 0);
            spin_unlock(&nlm_blocked_lock);
            svc_wake_up(block->b_daemon);
            return;
        }
    }
    spin_unlock(&nlm_blocked_lock);
    printk(KERN_WARNING "lockd: notification for unknown block!\n");
}

static int nlmsvc_same_owner(struct file_lock *fl1, struct file_lock *fl2)
{
    return fl1->fl_owner == fl2->fl_owner && fl1->fl_pid == fl2->fl_pid;
}

const struct lock_manager_operations nlmsvc_lock_operations = {
    .lm_compare_owner = nlmsvc_same_owner,
    .lm_notify = nlmsvc_notify_blocked,
    .lm_grant = nlmsvc_grant_deferred,
};

/*
 * Try to claim a lock that was previously blocked.
 *
 * Note that we use both the RPC_GRANTED_MSG call _and_ an async
 * RPC thread when notifying the client. This seems like overkill...
 * Here's why:
 *  -   we don't want to use a synchronous RPC thread, otherwise
 *  we might find ourselves hanging on a dead portmapper.
 *  -   Some lockd implementations (e.g. HP) don't react to
 *  RPC_GRANTED calls; they seem to insist on RPC_GRANTED_MSG calls.
 */
static void
nlmsvc_grant_blocked(struct nlm_block *block)
{
    struct nlm_file     *file = block->b_file;
    struct nlm_lock     *lock = &block->b_call->a_args.lock;
    int         error;

    dprintk("lockd: grant blocked lock %p\n", block);

    kref_get(&block->b_count);

    /* Unlink block request from list */
    nlmsvc_unlink_block(block);

    /* If b_granted is true this means we've been here before.
     * Just retry the grant callback, possibly refreshing the RPC
     * binding */
    if (block->b_granted) {
        nlm_rebind_host(block->b_host);
        goto callback;
    }

    /* Try the lock operation again */
    lock->fl.fl_flags |= FL_SLEEP;
    error = vfs_lock_file(file->f_file, F_SETLK, &lock->fl, NULL);
    lock->fl.fl_flags &= ~FL_SLEEP;

    switch (error) {
    case 0:
        break;
    case FILE_LOCK_DEFERRED:
        dprintk("lockd: lock still blocked error %d\n", error);
        nlmsvc_insert_block(block, NLM_NEVER);
        nlmsvc_release_block(block);
        return;
    default:
        printk(KERN_WARNING "lockd: unexpected error %d in %s!\n",
                -error, __func__);
        nlmsvc_insert_block(block, 10 * HZ);
        nlmsvc_release_block(block);
        return;
    }

callback:
    /* Lock was granted by VFS. */
    dprintk("lockd: GRANTing blocked lock.\n");
    block->b_granted = 1;

    /* keep block on the list, but don't reattempt until the RPC
     * completes or the submission fails
     */
    nlmsvc_insert_block(block, NLM_NEVER);

    /* Call the client -- use a soft RPC task since nlmsvc_retry_blocked
     * will queue up a new one if this one times out
     */
    error = nlm_async_call(block->b_call, NLMPROC_GRANTED_MSG,
                &nlmsvc_grant_ops);

    /* RPC submission failed, wait a bit and retry */
    if (error < 0)
        nlmsvc_insert_block(block, 10 * HZ);
}

/*
 * This is the callback from the RPC layer when the NLM_GRANTED_MSG
 * RPC call has succeeded or timed out.
 * Like all RPC callbacks, it is invoked by the rpciod process, so it
 * better not sleep. Therefore, we put the blocked lock on the nlm_blocked
 * chain once more in order to have it removed by lockd itself (which can
 * then sleep on the file semaphore without disrupting e.g. the nfs client).
 */
static void nlmsvc_grant_callback(struct rpc_task *task, void *data)
{
    struct nlm_rqst     *call = data;
    struct nlm_block    *block = call->a_block;
    unsigned long       timeout;

    dprintk("lockd: GRANT_MSG RPC callback\n");

    spin_lock(&nlm_blocked_lock);
    /* if the block is not on a list at this point then it has
     * been invalidated. Don't try to requeue it.
     *
     * FIXME: it's possible that the block is removed from the list
     * after this check but before the nlmsvc_insert_block. In that
     * case it will be added back. Perhaps we need better locking
     * for nlm_blocked?
     */
    if (list_empty(&block->b_list))
        goto out;

    /* Technically, we should down the file semaphore here. Since we
     * move the block towards the head of the queue only, no harm
     * can be done, though. */
    if (task->tk_status < 0) {
        /* RPC error: Re-insert for retransmission */
        timeout = 10 * HZ;
    } else {
        /* Call was successful, now wait for client callback */
        timeout = 60 * HZ;
    }
    nlmsvc_insert_block_locked(block, timeout);
    svc_wake_up(block->b_daemon);
out:
    spin_unlock(&nlm_blocked_lock);
}

/*
 * FIXME: nlmsvc_release_block() grabs a mutex.  This is not allowed for an
 * .rpc_release rpc_call_op
 */
static void nlmsvc_grant_release(void *data)
{
    struct nlm_rqst     *call = data;
    nlmsvc_release_block(call->a_block);
}

static const struct rpc_call_ops nlmsvc_grant_ops = {
    .rpc_call_done = nlmsvc_grant_callback,
    .rpc_release = nlmsvc_grant_release,
};

/*
 * We received a GRANT_RES callback. Try to find the corresponding
 * block.
 */
void
nlmsvc_grant_reply(struct nlm_cookie *cookie, __be32 status)
{
    struct nlm_block    *block;

    dprintk("grant_reply: looking for cookie %x, s=%d \n",
        *(unsigned int *)(cookie->data), status);
    if (!(block = nlmsvc_find_block(cookie)))
        return;

    if (block) {
        if (status == nlm_lck_denied_grace_period) {
            /* Try again in a couple of seconds */
            nlmsvc_insert_block(block, 10 * HZ);
        } else {
            /* Lock is now held by client, or has been rejected.
             * In both cases, the block should be removed. */
            nlmsvc_unlink_block(block);
        }
    }
    nlmsvc_release_block(block);
}

/* Helper function to handle retry of a deferred block.
 * If it is a blocking lock, call grant_blocked.
 * For a non-blocking lock or test lock, revisit the request.
 */
static void
retry_deferred_block(struct nlm_block *block)
{
    if (!(block->b_flags & B_GOT_CALLBACK))
        block->b_flags |= B_TIMED_OUT;
    nlmsvc_insert_block(block, NLM_TIMEOUT);
    dprintk("revisit block %p flags %d\n",  block, block->b_flags);
    if (block->b_deferred_req) {
        block->b_deferred_req->revisit(block->b_deferred_req, 0);
        block->b_deferred_req = NULL;
    }
}

/*
 * Retry all blocked locks that have been notified. This is where lockd
 * picks up locks that can be granted, or grant notifications that must
 * be retransmitted.
 */
unsigned long
nlmsvc_retry_blocked(void)
{
    unsigned long   timeout = MAX_SCHEDULE_TIMEOUT;
    struct nlm_block *block;

    while (!list_empty(&nlm_blocked) && !kthread_should_stop()) {
        block = list_entry(nlm_blocked.next, struct nlm_block, b_list);

        if (block->b_when == NLM_NEVER)
            break;
        if (time_after(block->b_when, jiffies)) {
            timeout = block->b_when - jiffies;
            break;
        }

        dprintk("nlmsvc_retry_blocked(%p, when=%ld)\n",
            block, block->b_when);
        if (block->b_flags & B_QUEUED) {
            dprintk("nlmsvc_retry_blocked delete block (%p, granted=%d, flags=%d)\n",
                block, block->b_granted, block->b_flags);
            retry_deferred_block(block);
        } else
            nlmsvc_grant_blocked(block);
    }

    return timeout;
}