linux/fs/lockd/svclock.c

// 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 <[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/exportfs.h>

#define NLMDBG_FACILITY …

#ifdef CONFIG_LOCKD_V4
#define nlm_deadlock …
#else
#define nlm_deadlock …
#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)
{ … }
#endif

/*
 * Insert a blocked lock into the global list
 */
static void
nlmsvc_insert_block_locked(struct nlm_block *block, unsigned long when)
{ … }

static void nlmsvc_insert_block(struct nlm_block *block, unsigned long when)
{ … }

/*
 * Remove a block from the global list
 */
static inline void
nlmsvc_remove_block(struct nlm_block *block)
{ … }

/*
 * Find a block for a given lock
 */
static struct nlm_block *
nlmsvc_lookup_block(struct nlm_file *file, struct nlm_lock *lock)
{ … }

static inline int nlm_cookie_match(struct nlm_cookie *a, struct nlm_cookie *b)
{ … }

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

/*
 * 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)
{ … }

/*
 * 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)
{ … }

static void nlmsvc_free_block(struct kref *kref)
{ … }

static void nlmsvc_release_block(struct nlm_block *block)
{ … }

/*
 * 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)
{ … }

static struct nlm_lockowner *
nlmsvc_get_lockowner(struct nlm_lockowner *lockowner)
{ … }

void nlmsvc_put_lockowner(struct nlm_lockowner *lockowner)
{ … }

static struct nlm_lockowner *__nlmsvc_find_lockowner(struct nlm_host *host, pid_t pid)
{ … }

static struct nlm_lockowner *nlmsvc_find_lockowner(struct nlm_host *host, pid_t pid)
{ … }

void
nlmsvc_release_lockowner(struct nlm_lock *lock)
{ … }

void nlmsvc_locks_init_private(struct file_lock *fl, struct nlm_host *host,
						pid_t 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)
{ … }

static void nlmsvc_freegrantargs(struct nlm_rqst *call)
{ … }

/*
 * Deferred lock request handling for non-blocking lock
 */
static __be32
nlmsvc_defer_lock_rqst(struct svc_rqst *rqstp, struct nlm_block *block)
{ … }

/*
 * 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)
{ … }

/*
 * 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)
{ … }

/*
 * 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)
{ … }

/*
 * 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)
{ … }

/*
 * 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)
{ … }

static int nlmsvc_grant_deferred(struct file_lock *fl, int result)
{ … }

/*
 * 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)
{ … }

static fl_owner_t nlmsvc_get_owner(fl_owner_t owner)
{ … }

static void nlmsvc_put_owner(fl_owner_t owner)
{ … }

const struct lock_manager_operations nlmsvc_lock_operations = …;

/*
 * 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)
{ … }

/*
 * 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)
{ … }

/*
 * 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)
{ … }

static const struct rpc_call_ops nlmsvc_grant_ops = …;

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

/* 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)
{ … }

/*
 * 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.
 */
void
nlmsvc_retry_blocked(struct svc_rqst *rqstp)
{ … }