Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1026 insertions, 0 deletions

diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
new file mode 100644
index 000000000..9c1aa7544
--- /dev/null
+++ b/fs/lockd/svclock.c
@@ -0,0 +1,1026 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 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 <okir@monad.swb.de>
+ */
+
+#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>
+#include <linux/exportfs.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);
+
+#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
+static const char *nlmdbg_cookie2a(const struct nlm_cookie *cookie)
+{
+	/*
+	 * We can get away with a static buffer because this is only called
+	 * from lockd, which is single-threaded.
+	 */
+	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;
+	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 = locks_delete_block(&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);
+}
+
+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);
+}
+
+static struct nlm_lockowner *
+nlmsvc_get_lockowner(struct nlm_lockowner *lockowner)
+{
+	refcount_inc(&lockowner->count);
+	return lockowner;
+}
+
+void nlmsvc_put_lockowner(struct nlm_lockowner *lockowner)
+{
+	if (!refcount_dec_and_lock(&lockowner->count, &lockowner->host->h_lock))
+		return;
+	list_del(&lockowner->list);
+	spin_unlock(&lockowner->host->h_lock);
+	nlmsvc_release_host(lockowner->host);
+	kfree(lockowner);
+}
+
+static struct nlm_lockowner *__nlmsvc_find_lockowner(struct nlm_host *host, pid_t pid)
+{
+	struct nlm_lockowner *lockowner;
+	list_for_each_entry(lockowner, &host->h_lockowners, list) {
+		if (lockowner->pid != pid)
+			continue;
+		return nlmsvc_get_lockowner(lockowner);
+	}
+	return NULL;
+}
+
+static struct nlm_lockowner *nlmsvc_find_lockowner(struct nlm_host *host, pid_t pid)
+{
+	struct nlm_lockowner *res, *new = NULL;
+
+	spin_lock(&host->h_lock);
+	res = __nlmsvc_find_lockowner(host, pid);
+
+	if (res == NULL) {
+		spin_unlock(&host->h_lock);
+		new = kmalloc(sizeof(*res), GFP_KERNEL);
+		spin_lock(&host->h_lock);
+		res = __nlmsvc_find_lockowner(host, pid);
+		if (res == NULL && new != NULL) {
+			res = new;
+			/* fs/locks.c will manage the refcount through lock_ops */
+			refcount_set(&new->count, 1);
+			new->pid = pid;
+			new->host = nlm_get_host(host);
+			list_add(&new->list, &host->h_lockowners);
+			new = NULL;
+		}
+	}
+
+	spin_unlock(&host->h_lock);
+	kfree(new);
+	return res;
+}
+
+void
+nlmsvc_release_lockowner(struct nlm_lock *lock)
+{
+	if (lock->fl.fl_owner)
+		nlmsvc_put_lockowner(lock->fl.fl_owner);
+}
+
+void nlmsvc_locks_init_private(struct file_lock *fl, struct nlm_host *host,
+						pid_t pid)
+{
+	fl->fl_owner = nlmsvc_find_lockowner(host, pid);
+}
+
+/*
+ * 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 = ((struct nlm_lockowner *)lock->fl.fl_owner)->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)
+{
+#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
+	struct inode		*inode = nlmsvc_file_inode(file);
+#endif
+	struct nlm_block	*block = NULL;
+	int			error;
+	int			mode;
+	int			async_block = 0;
+	__be32			ret;
+
+	dprintk("lockd: nlmsvc_lock(%s/%ld, ty=%d, pi=%d, %Ld-%Ld, bl=%d)\n",
+				inode->i_sb->s_id, inode->i_ino,
+				lock->fl.fl_type, lock->fl.fl_pid,
+				(long long)lock->fl.fl_start,
+				(long long)lock->fl.fl_end,
+				wait);
+
+	if (nlmsvc_file_file(file)->f_op->lock) {
+		async_block = wait;
+		wait = 0;
+	}
+
+	/* 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;
+	mode = lock_to_openmode(&lock->fl);
+	error = vfs_lock_file(file->f_file[mode], 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 = async_block ? nlm_lck_blocked : 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)
+{
+	int			error;
+	int			mode;
+	__be32			ret;
+
+	dprintk("lockd: nlmsvc_testlock(%s/%ld, ty=%d, %Ld-%Ld)\n",
+				nlmsvc_file_inode(file)->i_sb->s_id,
+				nlmsvc_file_inode(file)->i_ino,
+				lock->fl.fl_type,
+				(long long)lock->fl.fl_start,
+				(long long)lock->fl.fl_end);
+
+	if (locks_in_grace(SVC_NET(rqstp))) {
+		ret = nlm_lck_denied_grace_period;
+		goto out;
+	}
+
+	mode = lock_to_openmode(&lock->fl);
+	error = vfs_test_lock(file->f_file[mode], &lock->fl);
+	if (error) {
+		/* We can't currently deal with deferred test requests */
+		if (error == FILE_LOCK_DEFERRED)
+			WARN_ON_ONCE(1);
+
+		ret = nlm_lck_denied_nolocks;
+		goto out;
+	}
+
+	if (lock->fl.fl_type == F_UNLCK) {
+		ret = nlm_granted;
+		goto out;
+	}
+
+	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;
+	locks_release_private(&lock->fl);
+
+	ret = nlm_lck_denied;
+out:
+	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 = 0;
+
+	dprintk("lockd: nlmsvc_unlock(%s/%ld, pi=%d, %Ld-%Ld)\n",
+				nlmsvc_file_inode(file)->i_sb->s_id,
+				nlmsvc_file_inode(file)->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;
+	if (file->f_file[O_RDONLY])
+		error = vfs_lock_file(file->f_file[O_RDONLY], F_SETLK,
+					&lock->fl, NULL);
+	if (file->f_file[O_WRONLY])
+		error = vfs_lock_file(file->f_file[O_WRONLY], 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;
+	int mode;
+
+	dprintk("lockd: nlmsvc_cancel(%s/%ld, pi=%d, %Ld-%Ld)\n",
+				nlmsvc_file_inode(file)->i_sb->s_id,
+				nlmsvc_file_inode(file)->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) {
+		mode = lock_to_openmode(&lock->fl);
+		vfs_cancel_lock(block->b_file->f_file[mode],
+				&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 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, int result)
+{
+	block->b_flags |= B_GOT_CALLBACK;
+	if (result == 0)
+		block->b_granted = 1;
+	else
+		block->b_flags |= B_TIMED_OUT;
+}
+
+static int nlmsvc_grant_deferred(struct file_lock *fl, 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, 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 fl_owner_t nlmsvc_get_owner(fl_owner_t owner)
+{
+	return nlmsvc_get_lockowner(owner);
+}
+
+static void nlmsvc_put_owner(fl_owner_t owner)
+{
+	nlmsvc_put_lockowner(owner);
+}
+
+const struct lock_manager_operations nlmsvc_lock_operations = {
+	.lm_notify = nlmsvc_notify_blocked,
+	.lm_grant = nlmsvc_grant_deferred,
+	.lm_get_owner = nlmsvc_get_owner,
+	.lm_put_owner = nlmsvc_put_owner,
+};
+
+/*
+ * 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			mode;
+	int			error;
+	loff_t			fl_start, fl_end;
+
+	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 */
+	/* vfs_lock_file() can mangle fl_start and fl_end, but we need
+	 * them unchanged for the GRANT_MSG
+	 */
+	lock->fl.fl_flags |= FL_SLEEP;
+	fl_start = lock->fl.fl_start;
+	fl_end = lock->fl.fl_end;
+	mode = lock_to_openmode(&lock->fl);
+	error = vfs_lock_file(file->f_file[mode], F_SETLK, &lock->fl, NULL);
+	lock->fl.fl_flags &= ~FL_SLEEP;
+	lock->fl.fl_start = fl_start;
+	lock->fl.fl_end = fl_end;
+
+	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 (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;
+
+	spin_lock(&nlm_blocked_lock);
+	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;
+		}
+		spin_unlock(&nlm_blocked_lock);
+
+		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);
+		spin_lock(&nlm_blocked_lock);
+	}
+	spin_unlock(&nlm_blocked_lock);
+
+	return timeout;
+}