/*
   *  linux/fs/locks.c
   *
   *  Provide support for fcntl()'s F_GETLK, F_SETLK, and F_SETLKW calls.
   *  Doug Evans (dje@spiff.uucp), August 07, 1992
   *
   *  Deadlock detection added.
   *  FIXME: one thing isn't handled yet:
   *	- mandatory locks (requires lots of changes elsewhere)
   *  Kelly Carmichael (kelly@[142.24.8.65]), September 17, 1994.
   *
   *  Miscellaneous edits, and a total rewrite of posix_lock_file() code.
   *  Kai Petzke (wpp@marie.physik.tu-berlin.de), 1994
   *  
   *  Converted file_lock_table to a linked list from an array, which eliminates
   *  the limits on how many active file locks are open.
   *  Chad Page (pageone@netcom.com), November 27, 1994
   * 
   *  Removed dependency on file descriptors. dup()'ed file descriptors now
   *  get the same locks as the original file descriptors, and a close() on
   *  any file descriptor removes ALL the locks on the file for the current
   *  process. Since locks still depend on the process id, locks are inherited
   *  after an exec() but not after a fork(). This agrees with POSIX, and both
   *  BSD and SVR4 practice.
   *  Andy Walker (andy@lysaker.kvaerner.no), February 14, 1995
   *
   *  Scrapped free list which is redundant now that we allocate locks
   *  dynamically with kmalloc()/kfree().
   *  Andy Walker (andy@lysaker.kvaerner.no), February 21, 1995
   *
   *  Implemented two lock personalities - FL_FLOCK and FL_POSIX.
   *
   *  FL_POSIX locks are created with calls to fcntl() and lockf() through the
   *  fcntl() system call. They have the semantics described above.
   *
   *  FL_FLOCK locks are created with calls to flock(), through the flock()
   *  system call, which is new. Old C libraries implement flock() via fcntl()
   *  and will continue to use the old, broken implementation.
   *
   *  FL_FLOCK locks follow the 4.4 BSD flock() semantics. They are associated
   *  with a file pointer (filp). As a result they can be shared by a parent
   *  process and its children after a fork(). They are removed when the last
   *  file descriptor referring to the file pointer is closed (unless explicitly
   *  unlocked). 
   *
   *  FL_FLOCK locks never deadlock, an existing lock is always removed before
   *  upgrading from shared to exclusive (or vice versa). When this happens
   *  any processes blocked by the current lock are woken up and allowed to
   *  run before the new lock is applied.
   *  Andy Walker (andy@lysaker.kvaerner.no), June 09, 1995
   *
   *  Removed some race conditions in flock_lock_file(), marked other possible
   *  races. Just grep for FIXME to see them. 
   *  Dmitry Gorodchanin (pgmdsg@ibi.com), February 09, 1996.
   *
   *  Addressed Dmitry's concerns. Deadlock checking no longer recursive.
   *  Lock allocation changed to GFP_ATOMIC as we can't afford to sleep
   *  once we've checked for blocking and deadlocking.
   *  Andy Walker (andy@lysaker.kvaerner.no), April 03, 1996.
   *
   *  Initial implementation of mandatory locks. SunOS turned out to be
   *  a rotten model, so I implemented the "obvious" semantics.

   *  See 'Documentation/filesystems/mandatory-locking.txt' for details.

   *  Andy Walker (andy@lysaker.kvaerner.no), April 06, 1996.
   *
   *  Don't allow mandatory locks on mmap()'ed files. Added simple functions to
   *  check if a file has mandatory locks, used by mmap(), open() and creat() to
   *  see if system call should be rejected. Ref. HP-UX/SunOS/Solaris Reference
   *  Manual, Section 2.
   *  Andy Walker (andy@lysaker.kvaerner.no), April 09, 1996.
   *
   *  Tidied up block list handling. Added '/proc/locks' interface.
   *  Andy Walker (andy@lysaker.kvaerner.no), April 24, 1996.
   *
   *  Fixed deadlock condition for pathological code that mixes calls to
   *  flock() and fcntl().
   *  Andy Walker (andy@lysaker.kvaerner.no), April 29, 1996.
   *
   *  Allow only one type of locking scheme (FL_POSIX or FL_FLOCK) to be in use
   *  for a given file at a time. Changed the CONFIG_LOCK_MANDATORY scheme to
   *  guarantee sensible behaviour in the case where file system modules might
   *  be compiled with different options than the kernel itself.
   *  Andy Walker (andy@lysaker.kvaerner.no), May 15, 1996.
   *
   *  Added a couple of missing wake_up() calls. Thanks to Thomas Meckel
   *  (Thomas.Meckel@mni.fh-giessen.de) for spotting this.
   *  Andy Walker (andy@lysaker.kvaerner.no), May 15, 1996.
   *
   *  Changed FL_POSIX locks to use the block list in the same way as FL_FLOCK
   *  locks. Changed process synchronisation to avoid dereferencing locks that
   *  have already been freed.
   *  Andy Walker (andy@lysaker.kvaerner.no), Sep 21, 1996.
   *
   *  Made the block list a circular list to minimise searching in the list.
   *  Andy Walker (andy@lysaker.kvaerner.no), Sep 25, 1996.
   *
   *  Made mandatory locking a mount option. Default is not to allow mandatory
   *  locking.
   *  Andy Walker (andy@lysaker.kvaerner.no), Oct 04, 1996.
   *
   *  Some adaptations for NFS support.
   *  Olaf Kirch (okir@monad.swb.de), Dec 1996,
   *
   *  Fixed /proc/locks interface so that we can't overrun the buffer we are handed.
   *  Andy Walker (andy@lysaker.kvaerner.no), May 12, 1997.
   *
   *  Use slab allocator instead of kmalloc/kfree.
   *  Use generic list implementation from <linux/list.h>.
   *  Sped up posix_locks_deadlock by only considering blocked locks.
   *  Matthew Wilcox <willy@debian.org>, March, 2000.
   *
   *  Leases and LOCK_MAND
   *  Matthew Wilcox <willy@debian.org>, June, 2000.
   *  Stephen Rothwell <sfr@canb.auug.org.au>, June, 2000.
   */
  
  #include <linux/capability.h>
  #include <linux/file.h>

  #include <linux/fdtable.h>

  #include <linux/fs.h>
  #include <linux/init.h>

  #include <linux/security.h>
  #include <linux/slab.h>

  #include <linux/syscalls.h>
  #include <linux/time.h>

  #include <linux/rcupdate.h>

  #include <linux/pid_namespace.h>

  #include <linux/hashtable.h>

  #include <linux/percpu.h>

  #define CREATE_TRACE_POINTS
  #include <trace/events/filelock.h>

  #include <linux/uaccess.h>

  
  #define IS_POSIX(fl)	(fl->fl_flags & FL_POSIX)
  #define IS_FLOCK(fl)	(fl->fl_flags & FL_FLOCK)

  #define IS_LEASE(fl)	(fl->fl_flags & (FL_LEASE|FL_DELEG|FL_LAYOUT))

  #define IS_OFDLCK(fl)	(fl->fl_flags & FL_OFDLCK)

  #define IS_REMOTELCK(fl)	(fl->fl_pid <= 0)

  static bool lease_breaking(struct file_lock *fl)
  {

  	return fl->fl_flags & (FL_UNLOCK_PENDING | FL_DOWNGRADE_PENDING);
  }
  
  static int target_leasetype(struct file_lock *fl)
  {
  	if (fl->fl_flags & FL_UNLOCK_PENDING)
  		return F_UNLCK;
  	if (fl->fl_flags & FL_DOWNGRADE_PENDING)
  		return F_RDLCK;
  	return fl->fl_type;

  }

  int leases_enable = 1;
  int lease_break_time = 45;

  /*

   * The global file_lock_list is only used for displaying /proc/locks, so we

   * keep a list on each CPU, with each list protected by its own spinlock.
   * Global serialization is done using file_rwsem.
   *
   * Note that alterations to the list also require that the relevant flc_lock is
   * held.

   */

  struct file_lock_list_struct {
  	spinlock_t		lock;
  	struct hlist_head	hlist;
  };
  static DEFINE_PER_CPU(struct file_lock_list_struct, file_lock_list);

  DEFINE_STATIC_PERCPU_RWSEM(file_rwsem);

  /*

   * The blocked_hash is used to find POSIX lock loops for deadlock detection.

   * It is protected by blocked_lock_lock.

   *
   * We hash locks by lockowner in order to optimize searching for the lock a
   * particular lockowner is waiting on.
   *
   * FIXME: make this value scale via some heuristic? We generally will want more
   * buckets when we have more lockowners holding locks, but that's a little
   * difficult to determine without knowing what the workload will look like.

   */

  #define BLOCKED_HASH_BITS	7
  static DEFINE_HASHTABLE(blocked_hash, BLOCKED_HASH_BITS);

  /*

   * This lock protects the blocked_hash. Generally, if you're accessing it, you
   * want to be holding this lock.

   *
   * In addition, it also protects the fl->fl_block list, and the fl->fl_next
   * pointer for file_lock structures that are acting as lock requests (in
   * contrast to those that are acting as records of acquired locks).
   *
   * Note that when we acquire this lock in order to change the above fields,

   * we often hold the flc_lock as well. In certain cases, when reading the fields

   * protected by this lock, we can skip acquiring it iff we already hold the

   * flc_lock.

   */

  static DEFINE_SPINLOCK(blocked_lock_lock);

  static struct kmem_cache *flctx_cache __read_mostly;

  static struct kmem_cache *filelock_cache __read_mostly;

  static struct file_lock_context *

  locks_get_lock_context(struct inode *inode, int type)

  {

  	struct file_lock_context *ctx;

  	/* paired with cmpxchg() below */
  	ctx = smp_load_acquire(&inode->i_flctx);
  	if (likely(ctx) || type == F_UNLCK)

  		goto out;

  	ctx = kmem_cache_alloc(flctx_cache, GFP_KERNEL);
  	if (!ctx)

  		goto out;

  	spin_lock_init(&ctx->flc_lock);
  	INIT_LIST_HEAD(&ctx->flc_flock);
  	INIT_LIST_HEAD(&ctx->flc_posix);
  	INIT_LIST_HEAD(&ctx->flc_lease);

  
  	/*
  	 * Assign the pointer if it's not already assigned. If it is, then
  	 * free the context we just allocated.
  	 */

  	if (cmpxchg(&inode->i_flctx, NULL, ctx)) {
  		kmem_cache_free(flctx_cache, ctx);
  		ctx = smp_load_acquire(&inode->i_flctx);
  	}

  out:

  	trace_locks_get_lock_context(inode, type, ctx);

  	return ctx;

  }

  static void
  locks_dump_ctx_list(struct list_head *list, char *list_type)
  {
  	struct file_lock *fl;
  
  	list_for_each_entry(fl, list, fl_list) {
  		pr_warn("%s: fl_owner=%p fl_flags=0x%x fl_type=0x%x fl_pid=%u
  ", list_type, fl->fl_owner, fl->fl_flags, fl->fl_type, fl->fl_pid);
  	}
  }
  
  static void
  locks_check_ctx_lists(struct inode *inode)
  {
  	struct file_lock_context *ctx = inode->i_flctx;
  
  	if (unlikely(!list_empty(&ctx->flc_flock) ||
  		     !list_empty(&ctx->flc_posix) ||
  		     !list_empty(&ctx->flc_lease))) {
  		pr_warn("Leaked locks on dev=0x%x:0x%x ino=0x%lx:
  ",
  			MAJOR(inode->i_sb->s_dev), MINOR(inode->i_sb->s_dev),
  			inode->i_ino);
  		locks_dump_ctx_list(&ctx->flc_flock, "FLOCK");
  		locks_dump_ctx_list(&ctx->flc_posix, "POSIX");
  		locks_dump_ctx_list(&ctx->flc_lease, "LEASE");
  	}
  }

  static void
  locks_check_ctx_file_list(struct file *filp, struct list_head *list,
  				char *list_type)
  {
  	struct file_lock *fl;
  	struct inode *inode = locks_inode(filp);
  
  	list_for_each_entry(fl, list, fl_list)
  		if (fl->fl_file == filp)
  			pr_warn("Leaked %s lock on dev=0x%x:0x%x ino=0x%lx "
  				" fl_owner=%p fl_flags=0x%x fl_type=0x%x fl_pid=%u
  ",
  				list_type, MAJOR(inode->i_sb->s_dev),
  				MINOR(inode->i_sb->s_dev), inode->i_ino,
  				fl->fl_owner, fl->fl_flags, fl->fl_type, fl->fl_pid);
  }

  void

  locks_free_lock_context(struct inode *inode)

  {

  	struct file_lock_context *ctx = inode->i_flctx;

  	if (unlikely(ctx)) {
  		locks_check_ctx_lists(inode);

  		kmem_cache_free(flctx_cache, ctx);
  	}
  }

  static void locks_init_lock_heads(struct file_lock *fl)

  {

  	INIT_HLIST_NODE(&fl->fl_link);

  	INIT_LIST_HEAD(&fl->fl_list);

  	INIT_LIST_HEAD(&fl->fl_block);
  	init_waitqueue_head(&fl->fl_wait);

  }

  /* Allocate an empty lock structure. */

  struct file_lock *locks_alloc_lock(void)

  {

  	struct file_lock *fl = kmem_cache_zalloc(filelock_cache, GFP_KERNEL);

  
  	if (fl)

  		locks_init_lock_heads(fl);

  
  	return fl;

  }

  EXPORT_SYMBOL_GPL(locks_alloc_lock);

  void locks_release_private(struct file_lock *fl)

  {
  	if (fl->fl_ops) {
  		if (fl->fl_ops->fl_release_private)
  			fl->fl_ops->fl_release_private(fl);
  		fl->fl_ops = NULL;
  	}

  	if (fl->fl_lmops) {

  		if (fl->fl_lmops->lm_put_owner) {
  			fl->fl_lmops->lm_put_owner(fl->fl_owner);
  			fl->fl_owner = NULL;
  		}

  		fl->fl_lmops = NULL;
  	}

  }

  EXPORT_SYMBOL_GPL(locks_release_private);

  /* Free a lock which is not in use. */

  void locks_free_lock(struct file_lock *fl)

  {

  	BUG_ON(waitqueue_active(&fl->fl_wait));

  	BUG_ON(!list_empty(&fl->fl_list));

  	BUG_ON(!list_empty(&fl->fl_block));

  	BUG_ON(!hlist_unhashed(&fl->fl_link));

  	locks_release_private(fl);

  	kmem_cache_free(filelock_cache, fl);
  }

  EXPORT_SYMBOL(locks_free_lock);

  static void
  locks_dispose_list(struct list_head *dispose)
  {
  	struct file_lock *fl;
  
  	while (!list_empty(dispose)) {

  		fl = list_first_entry(dispose, struct file_lock, fl_list);
  		list_del_init(&fl->fl_list);

  		locks_free_lock(fl);
  	}
  }

  void locks_init_lock(struct file_lock *fl)
  {

  	memset(fl, 0, sizeof(struct file_lock));
  	locks_init_lock_heads(fl);

  }
  
  EXPORT_SYMBOL(locks_init_lock);

  /*
   * Initialize a new lock from an existing file_lock structure.
   */

  void locks_copy_conflock(struct file_lock *new, struct file_lock *fl)

  {
  	new->fl_owner = fl->fl_owner;
  	new->fl_pid = fl->fl_pid;

  	new->fl_file = NULL;

  	new->fl_flags = fl->fl_flags;
  	new->fl_type = fl->fl_type;
  	new->fl_start = fl->fl_start;
  	new->fl_end = fl->fl_end;

  	new->fl_lmops = fl->fl_lmops;

  	new->fl_ops = NULL;

  
  	if (fl->fl_lmops) {
  		if (fl->fl_lmops->lm_get_owner)

  			fl->fl_lmops->lm_get_owner(fl->fl_owner);

  	}

  }

  EXPORT_SYMBOL(locks_copy_conflock);

  
  void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
  {

  	/* "new" must be a freshly-initialized lock */
  	WARN_ON_ONCE(new->fl_ops);

  	locks_copy_conflock(new, fl);

  	new->fl_file = fl->fl_file;

  	new->fl_ops = fl->fl_ops;

  	if (fl->fl_ops) {
  		if (fl->fl_ops->fl_copy_lock)
  			fl->fl_ops->fl_copy_lock(new, fl);
  	}

  }
  
  EXPORT_SYMBOL(locks_copy_lock);
  
  static inline int flock_translate_cmd(int cmd) {
  	if (cmd & LOCK_MAND)
  		return cmd & (LOCK_MAND | LOCK_RW);
  	switch (cmd) {
  	case LOCK_SH:
  		return F_RDLCK;
  	case LOCK_EX:
  		return F_WRLCK;
  	case LOCK_UN:
  		return F_UNLCK;
  	}
  	return -EINVAL;
  }
  
  /* Fill in a file_lock structure with an appropriate FLOCK lock. */

  static struct file_lock *
  flock_make_lock(struct file *filp, unsigned int cmd)

  {
  	struct file_lock *fl;
  	int type = flock_translate_cmd(cmd);

  	if (type < 0)

  		return ERR_PTR(type);

  	
  	fl = locks_alloc_lock();
  	if (fl == NULL)

  		return ERR_PTR(-ENOMEM);

  
  	fl->fl_file = filp;

  	fl->fl_owner = filp;

  	fl->fl_pid = current->tgid;
  	fl->fl_flags = FL_FLOCK;
  	fl->fl_type = type;
  	fl->fl_end = OFFSET_MAX;
  	

  	return fl;

  }

  static int assign_type(struct file_lock *fl, long type)

  {
  	switch (type) {
  	case F_RDLCK:
  	case F_WRLCK:
  	case F_UNLCK:
  		fl->fl_type = type;
  		break;
  	default:
  		return -EINVAL;
  	}
  	return 0;
  }

  static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
  				 struct flock64 *l)

  {

  	switch (l->l_whence) {

  	case SEEK_SET:

  		fl->fl_start = 0;

  		break;

  	case SEEK_CUR:

  		fl->fl_start = filp->f_pos;

  		break;

  	case SEEK_END:

  		fl->fl_start = i_size_read(file_inode(filp));

  		break;
  	default:
  		return -EINVAL;
  	}

  	if (l->l_start > OFFSET_MAX - fl->fl_start)
  		return -EOVERFLOW;
  	fl->fl_start += l->l_start;
  	if (fl->fl_start < 0)
  		return -EINVAL;

  
  	/* POSIX-1996 leaves the case l->l_len < 0 undefined;
  	   POSIX-2001 defines it. */

  	if (l->l_len > 0) {

  		if (l->l_len - 1 > OFFSET_MAX - fl->fl_start)
  			return -EOVERFLOW;
  		fl->fl_end = fl->fl_start + l->l_len - 1;

  	} else if (l->l_len < 0) {

  		if (fl->fl_start + l->l_len < 0)

  			return -EINVAL;

  		fl->fl_end = fl->fl_start - 1;
  		fl->fl_start += l->l_len;
  	} else
  		fl->fl_end = OFFSET_MAX;

  	fl->fl_owner = current->files;
  	fl->fl_pid = current->tgid;
  	fl->fl_file = filp;
  	fl->fl_flags = FL_POSIX;
  	fl->fl_ops = NULL;
  	fl->fl_lmops = NULL;
  
  	return assign_type(fl, l->l_type);
  }

  /* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
   * style lock.
   */
  static int flock_to_posix_lock(struct file *filp, struct file_lock *fl,
  			       struct flock *l)

  {

  	struct flock64 ll = {
  		.l_type = l->l_type,
  		.l_whence = l->l_whence,
  		.l_start = l->l_start,
  		.l_len = l->l_len,
  	};
  
  	return flock64_to_posix_lock(filp, fl, &ll);

  }

  
  /* default lease lock manager operations */

  static bool
  lease_break_callback(struct file_lock *fl)

  {
  	kill_fasync(&fl->fl_fasync, SIGIO, POLL_MSG);

  	return false;

  }

  static void
  lease_setup(struct file_lock *fl, void **priv)
  {
  	struct file *filp = fl->fl_file;
  	struct fasync_struct *fa = *priv;
  
  	/*
  	 * fasync_insert_entry() returns the old entry if any. If there was no
  	 * old entry, then it used "priv" and inserted it into the fasync list.
  	 * Clear the pointer to indicate that it shouldn't be freed.
  	 */
  	if (!fasync_insert_entry(fa->fa_fd, filp, &fl->fl_fasync, fa))
  		*priv = NULL;

  	__f_setown(filp, task_pid(current), PIDTYPE_TGID, 0);

  }

  static const struct lock_manager_operations lease_manager_ops = {

  	.lm_break = lease_break_callback,

  	.lm_change = lease_modify,

  	.lm_setup = lease_setup,

  };
  
  /*
   * Initialize a lease, use the default lock manager operations
   */

  static int lease_init(struct file *filp, long type, struct file_lock *fl)

  {

  	if (assign_type(fl, type) != 0)
  		return -EINVAL;

  	fl->fl_owner = filp;

  	fl->fl_pid = current->tgid;
  
  	fl->fl_file = filp;
  	fl->fl_flags = FL_LEASE;

  	fl->fl_start = 0;
  	fl->fl_end = OFFSET_MAX;
  	fl->fl_ops = NULL;
  	fl->fl_lmops = &lease_manager_ops;
  	return 0;
  }
  
  /* Allocate a file_lock initialised to this type of lease */

  static struct file_lock *lease_alloc(struct file *filp, long type)

  {
  	struct file_lock *fl = locks_alloc_lock();

  	int error = -ENOMEM;

  
  	if (fl == NULL)

  		return ERR_PTR(error);

  
  	error = lease_init(filp, type, fl);

  	if (error) {
  		locks_free_lock(fl);

  		return ERR_PTR(error);

  	}

  	return fl;

  }
  
  /* Check if two locks overlap each other.
   */
  static inline int locks_overlap(struct file_lock *fl1, struct file_lock *fl2)
  {
  	return ((fl1->fl_end >= fl2->fl_start) &&
  		(fl2->fl_end >= fl1->fl_start));
  }
  
  /*
   * Check whether two locks have the same owner.
   */

  static int posix_same_owner(struct file_lock *fl1, struct file_lock *fl2)

  {

  	if (fl1->fl_lmops && fl1->fl_lmops->lm_compare_owner)

  		return fl2->fl_lmops == fl1->fl_lmops &&

  			fl1->fl_lmops->lm_compare_owner(fl1, fl2);

  	return fl1->fl_owner == fl2->fl_owner;
  }

  /* Must be called with the flc_lock held! */

  static void locks_insert_global_locks(struct file_lock *fl)

  {

  	struct file_lock_list_struct *fll = this_cpu_ptr(&file_lock_list);

  	percpu_rwsem_assert_held(&file_rwsem);

  	spin_lock(&fll->lock);

  	fl->fl_link_cpu = smp_processor_id();

  	hlist_add_head(&fl->fl_link, &fll->hlist);
  	spin_unlock(&fll->lock);

  }

  /* Must be called with the flc_lock held! */

  static void locks_delete_global_locks(struct file_lock *fl)

  {

  	struct file_lock_list_struct *fll;

  	percpu_rwsem_assert_held(&file_rwsem);

  	/*
  	 * Avoid taking lock if already unhashed. This is safe since this check

  	 * is done while holding the flc_lock, and new insertions into the list

  	 * also require that it be held.
  	 */
  	if (hlist_unhashed(&fl->fl_link))
  		return;

  
  	fll = per_cpu_ptr(&file_lock_list, fl->fl_link_cpu);
  	spin_lock(&fll->lock);

  	hlist_del_init(&fl->fl_link);

  	spin_unlock(&fll->lock);

  }

  static unsigned long
  posix_owner_key(struct file_lock *fl)
  {
  	if (fl->fl_lmops && fl->fl_lmops->lm_owner_key)
  		return fl->fl_lmops->lm_owner_key(fl);
  	return (unsigned long)fl->fl_owner;
  }

  static void locks_insert_global_blocked(struct file_lock *waiter)

  {

  	lockdep_assert_held(&blocked_lock_lock);

  	hash_add(blocked_hash, &waiter->fl_link, posix_owner_key(waiter));

  }

  static void locks_delete_global_blocked(struct file_lock *waiter)

  {

  	lockdep_assert_held(&blocked_lock_lock);

  	hash_del(&waiter->fl_link);

  }

  /* Remove waiter from blocker's block list.
   * When blocker ends up pointing to itself then the list is empty.

   *

   * Must be called with blocked_lock_lock held.

   */

  static void __locks_delete_block(struct file_lock *waiter)

  {

  	locks_delete_global_blocked(waiter);

  	list_del_init(&waiter->fl_block);

  	waiter->fl_next = NULL;
  }

  static void locks_delete_block(struct file_lock *waiter)

  {

  	spin_lock(&blocked_lock_lock);

  	__locks_delete_block(waiter);

  	spin_unlock(&blocked_lock_lock);

  }
  
  /* Insert waiter into blocker's block list.
   * We use a circular list so that processes can be easily woken up in
   * the order they blocked. The documentation doesn't require this but
   * it seems like the reasonable thing to do.

   *

   * Must be called with both the flc_lock and blocked_lock_lock held. The
   * fl_block list itself is protected by the blocked_lock_lock, but by ensuring
   * that the flc_lock is also held on insertions we can avoid taking the
   * blocked_lock_lock in some cases when we see that the fl_block list is empty.

   */

  static void __locks_insert_block(struct file_lock *blocker,
  					struct file_lock *waiter)

  {

  	BUG_ON(!list_empty(&waiter->fl_block));

  	waiter->fl_next = blocker;

  	list_add_tail(&waiter->fl_block, &blocker->fl_block);

  	if (IS_POSIX(blocker) && !IS_OFDLCK(blocker))

  		locks_insert_global_blocked(waiter);
  }

  /* Must be called with flc_lock held. */

  static void locks_insert_block(struct file_lock *blocker,
  					struct file_lock *waiter)
  {

  	spin_lock(&blocked_lock_lock);

  	__locks_insert_block(blocker, waiter);

  	spin_unlock(&blocked_lock_lock);

  }

  /*
   * Wake up processes blocked waiting for blocker.
   *

   * Must be called with the inode->flc_lock held!

   */
  static void locks_wake_up_blocks(struct file_lock *blocker)
  {

  	/*
  	 * Avoid taking global lock if list is empty. This is safe since new

  	 * blocked requests are only added to the list under the flc_lock, and
  	 * the flc_lock is always held here. Note that removal from the fl_block
  	 * list does not require the flc_lock, so we must recheck list_empty()

  	 * after acquiring the blocked_lock_lock.

  	 */
  	if (list_empty(&blocker->fl_block))
  		return;

  	spin_lock(&blocked_lock_lock);

  	while (!list_empty(&blocker->fl_block)) {

  		struct file_lock *waiter;
  
  		waiter = list_first_entry(&blocker->fl_block,

  				struct file_lock, fl_block);
  		__locks_delete_block(waiter);

  		if (waiter->fl_lmops && waiter->fl_lmops->lm_notify)
  			waiter->fl_lmops->lm_notify(waiter);

  		else
  			wake_up(&waiter->fl_wait);
  	}

  	spin_unlock(&blocked_lock_lock);

  }

  static void

  locks_insert_lock_ctx(struct file_lock *fl, struct list_head *before)

  {

  	list_add_tail(&fl->fl_list, before);
  	locks_insert_global_locks(fl);
  }

  static void

  locks_unlink_lock_ctx(struct file_lock *fl)

  {

  	locks_delete_global_locks(fl);

  	list_del_init(&fl->fl_list);

  	locks_wake_up_blocks(fl);

  }

  static void

  locks_delete_lock_ctx(struct file_lock *fl, struct list_head *dispose)

  {

  	locks_unlink_lock_ctx(fl);

  	if (dispose)

  		list_add(&fl->fl_list, dispose);

  	else
  		locks_free_lock(fl);

  }
  
  /* Determine if lock sys_fl blocks lock caller_fl. Common functionality
   * checks for shared/exclusive status of overlapping locks.
   */
  static int locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
  {
  	if (sys_fl->fl_type == F_WRLCK)
  		return 1;
  	if (caller_fl->fl_type == F_WRLCK)
  		return 1;
  	return 0;
  }
  
  /* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
   * checking before calling the locks_conflict().
   */
  static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
  {
  	/* POSIX locks owned by the same process do not conflict with
  	 * each other.
  	 */

  	if (posix_same_owner(caller_fl, sys_fl))

  		return (0);
  
  	/* Check whether they overlap */
  	if (!locks_overlap(caller_fl, sys_fl))
  		return 0;
  
  	return (locks_conflict(caller_fl, sys_fl));
  }
  
  /* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
   * checking before calling the locks_conflict().
   */
  static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
  {
  	/* FLOCK locks referring to the same filp do not conflict with
  	 * each other.
  	 */

  	if (caller_fl->fl_file == sys_fl->fl_file)

  		return (0);
  	if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND))
  		return 0;
  
  	return (locks_conflict(caller_fl, sys_fl));
  }

  void

  posix_test_lock(struct file *filp, struct file_lock *fl)

  {
  	struct file_lock *cfl;

  	struct file_lock_context *ctx;

  	struct inode *inode = locks_inode(filp);

  	ctx = smp_load_acquire(&inode->i_flctx);

  	if (!ctx || list_empty_careful(&ctx->flc_posix)) {
  		fl->fl_type = F_UNLCK;
  		return;
  	}

  	spin_lock(&ctx->flc_lock);

  	list_for_each_entry(cfl, &ctx->flc_posix, fl_list) {
  		if (posix_locks_conflict(fl, cfl)) {
  			locks_copy_conflock(fl, cfl);

  			goto out;
  		}

  	}

  	fl->fl_type = F_UNLCK;
  out:

  	spin_unlock(&ctx->flc_lock);

  	return;

  }

  EXPORT_SYMBOL(posix_test_lock);

  /*
   * Deadlock detection:
   *
   * We attempt to detect deadlocks that are due purely to posix file
   * locks.

   *

   * We assume that a task can be waiting for at most one lock at a time.
   * So for any acquired lock, the process holding that lock may be
   * waiting on at most one other lock.  That lock in turns may be held by
   * someone waiting for at most one other lock.  Given a requested lock
   * caller_fl which is about to wait for a conflicting lock block_fl, we
   * follow this chain of waiters to ensure we are not about to create a
   * cycle.

   *

   * Since we do this before we ever put a process to sleep on a lock, we
   * are ensured that there is never a cycle; that is what guarantees that
   * the while() loop in posix_locks_deadlock() eventually completes.

   *

   * Note: the above assumption may not be true when handling lock
   * requests from a broken NFS client. It may also fail in the presence
   * of tasks (such as posix threads) sharing the same open file table.

   * To handle those cases, we just bail out after a few iterations.

   *

   * For FL_OFDLCK locks, the owner is the filp, not the files_struct.

   * Because the owner is not even nominally tied to a thread of
   * execution, the deadlock detection below can't reasonably work well. Just
   * skip it for those.
   *

   * In principle, we could do a more limited deadlock detection on FL_OFDLCK

   * locks that just checks for the case where two tasks are attempting to
   * upgrade from read to write locks on the same inode.

   */

  
  #define MAX_DEADLK_ITERATIONS 10

  /* Find a lock that the owner of the given block_fl is blocking on. */
  static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
  {
  	struct file_lock *fl;

  	hash_for_each_possible(blocked_hash, fl, fl_link, posix_owner_key(block_fl)) {

  		if (posix_same_owner(fl, block_fl))
  			return fl->fl_next;
  	}
  	return NULL;
  }

  /* Must be called with the blocked_lock_lock held! */

  static int posix_locks_deadlock(struct file_lock *caller_fl,

  				struct file_lock *block_fl)
  {

  	int i = 0;

  	lockdep_assert_held(&blocked_lock_lock);

  	/*
  	 * This deadlock detector can't reasonably detect deadlocks with

  	 * FL_OFDLCK locks, since they aren't owned by a process, per-se.

  	 */

  	if (IS_OFDLCK(caller_fl))

  		return 0;

  	while ((block_fl = what_owner_is_waiting_for(block_fl))) {
  		if (i++ > MAX_DEADLK_ITERATIONS)
  			return 0;
  		if (posix_same_owner(caller_fl, block_fl))
  			return 1;

  	}
  	return 0;
  }

  /* Try to create a FLOCK lock on filp. We always insert new FLOCK locks

   * after any leases, but before any posix locks.

   *
   * Note that if called with an FL_EXISTS argument, the caller may determine
   * whether or not a lock was successfully freed by testing the return
   * value for -ENOENT.

   */

  static int flock_lock_inode(struct inode *inode, struct file_lock *request)

  {

  	struct file_lock *new_fl = NULL;

  	struct file_lock *fl;
  	struct file_lock_context *ctx;

  	int error = 0;

  	bool found = false;

  	LIST_HEAD(dispose);

  	ctx = locks_get_lock_context(inode, request->fl_type);
  	if (!ctx) {
  		if (request->fl_type != F_UNLCK)
  			return -ENOMEM;
  		return (request->fl_flags & FL_EXISTS) ? -ENOENT : 0;
  	}

  	if (!(request->fl_flags & FL_ACCESS) && (request->fl_type != F_UNLCK)) {

  		new_fl = locks_alloc_lock();

  		if (!new_fl)
  			return -ENOMEM;

  	}

  	percpu_down_read_preempt_disable(&file_rwsem);

  	spin_lock(&ctx->flc_lock);

  	if (request->fl_flags & FL_ACCESS)
  		goto find_conflict;

  	list_for_each_entry(fl, &ctx->flc_flock, fl_list) {

  		if (request->fl_file != fl->fl_file)

  			continue;

  		if (request->fl_type == fl->fl_type)

  			goto out;

  		found = true;

  		locks_delete_lock_ctx(fl, &dispose);

  		break;
  	}

  	if (request->fl_type == F_UNLCK) {
  		if ((request->fl_flags & FL_EXISTS) && !found)
  			error = -ENOENT;

  		goto out;

  	}

  find_conflict:

  	list_for_each_entry(fl, &ctx->flc_flock, fl_list) {

  		if (!flock_locks_conflict(request, fl))

  			continue;
  		error = -EAGAIN;

  		if (!(request->fl_flags & FL_SLEEP))
  			goto out;
  		error = FILE_LOCK_DEFERRED;
  		locks_insert_block(fl, request);

  		goto out;
  	}

  	if (request->fl_flags & FL_ACCESS)
  		goto out;

  	locks_copy_lock(new_fl, request);

  	locks_insert_lock_ctx(new_fl, &ctx->flc_flock);

  	new_fl = NULL;

  	error = 0;

  
  out:

  	spin_unlock(&ctx->flc_lock);

  	percpu_up_read_preempt_enable(&file_rwsem);

  	if (new_fl)
  		locks_free_lock(new_fl);

  	locks_dispose_list(&dispose);

  	trace_flock_lock_inode(inode, request, error);

  	return error;
  }

  static int posix_lock_inode(struct inode *inode, struct file_lock *request,
  			    struct file_lock *conflock)

  {

  	struct file_lock *fl, *tmp;

  	struct file_lock *new_fl = NULL;
  	struct file_lock *new_fl2 = NULL;

  	struct file_lock *left = NULL;
  	struct file_lock *right = NULL;

  	struct file_lock_context *ctx;

  	int error;
  	bool added = false;

  	LIST_HEAD(dispose);

  	ctx = locks_get_lock_context(inode, request->fl_type);

  	if (!ctx)

  		return (request->fl_type == F_UNLCK) ? 0 : -ENOMEM;

  	/*
  	 * We may need two file_lock structures for this operation,
  	 * so we get them in advance to avoid races.

  	 *
  	 * In some cases we can be sure, that no new locks will be needed

  	 */

  	if (!(request->fl_flags & FL_ACCESS) &&
  	    (request->fl_type != F_UNLCK ||
  	     request->fl_start != 0 || request->fl_end != OFFSET_MAX)) {
  		new_fl = locks_alloc_lock();
  		new_fl2 = locks_alloc_lock();
  	}

  	percpu_down_read_preempt_disable(&file_rwsem);

  	spin_lock(&ctx->flc_lock);

  	/*
  	 * New lock request. Walk all POSIX locks and look for conflicts. If
  	 * there are any, either return error or put the request on the

  	 * blocker's list of waiters and the global blocked_hash.

  	 */

  	if (request->fl_type != F_UNLCK) {

  		list_for_each_entry(fl, &ctx->flc_posix, fl_list) {

  			if (!posix_locks_conflict(request, fl))
  				continue;

  			if (conflock)

  				locks_copy_conflock(conflock, fl);

  			error = -EAGAIN;
  			if (!(request->fl_flags & FL_SLEEP))
  				goto out;

  			/*
  			 * Deadlock detection and insertion into the blocked
  			 * locks list must be done while holding the same lock!
  			 */

  			error = -EDEADLK;

  			spin_lock(&blocked_lock_lock);

  			if (likely(!posix_locks_deadlock(request, fl))) {
  				error = FILE_LOCK_DEFERRED;
  				__locks_insert_block(fl, request);
  			}

  			spin_unlock(&blocked_lock_lock);

  			goto out;
    		}
    	}
  
  	/* If we're just looking for a conflict, we're done. */
  	error = 0;
  	if (request->fl_flags & FL_ACCESS)
  		goto out;

  	/* Find the first old lock with the same owner as the new lock */
  	list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
  		if (posix_same_owner(request, fl))
  			break;

  	}

  	/* Process locks with this owner. */

  	list_for_each_entry_safe_from(fl, tmp, &ctx->flc_posix, fl_list) {
  		if (!posix_same_owner(request, fl))
  			break;
  
  		/* Detect adjacent or overlapping regions (if same lock type) */

  		if (request->fl_type == fl->fl_type) {

  			/* In all comparisons of start vs end, use
  			 * "start - 1" rather than "end + 1". If end
  			 * is OFFSET_MAX, end + 1 will become negative.
  			 */

  			if (fl->fl_end < request->fl_start - 1)

  				continue;

  			/* If the next lock in the list has entirely bigger
  			 * addresses than the new one, insert the lock here.
  			 */

  			if (fl->fl_start - 1 > request->fl_end)

  				break;
  
  			/* If we come here, the new and old lock are of the
  			 * same type and adjacent or overlapping. Make one
  			 * lock yielding from the lower start address of both
  			 * locks to the higher end address.
  			 */
  			if (fl->fl_start > request->fl_start)
  				fl->fl_start = request->fl_start;
  			else
  				request->fl_start = fl->fl_start;
  			if (fl->fl_end < request->fl_end)
  				fl->fl_end = request->fl_end;
  			else
  				request->fl_end = fl->fl_end;
  			if (added) {

  				locks_delete_lock_ctx(fl, &dispose);

  				continue;
  			}
  			request = fl;

  			added = true;

  		} else {

  			/* Processing for different lock types is a bit
  			 * more complex.
  			 */
  			if (fl->fl_end < request->fl_start)

  				continue;

  			if (fl->fl_start > request->fl_end)
  				break;
  			if (request->fl_type == F_UNLCK)

  				added = true;

  			if (fl->fl_start < request->fl_start)
  				left = fl;
  			/* If the next lock in the list has a higher end
  			 * address than the new one, insert the new one here.
  			 */
  			if (fl->fl_end > request->fl_end) {
  				right = fl;
  				break;
  			}
  			if (fl->fl_start >= request->fl_start) {
  				/* The new lock completely replaces an old
  				 * one (This may happen several times).
  				 */
  				if (added) {

  					locks_delete_lock_ctx(fl, &dispose);

  					continue;
  				}

  				/*
  				 * Replace the old lock with new_fl, and
  				 * remove the old one. It's safe to do the
  				 * insert here since we know that we won't be
  				 * using new_fl later, and that the lock is
  				 * just replacing an existing lock.

  				 */

  				error = -ENOLCK;
  				if (!new_fl)
  					goto out;
  				locks_copy_lock(new_fl, request);
  				request = new_fl;
  				new_fl = NULL;

  				locks_insert_lock_ctx(request, &fl->fl_list);
  				locks_delete_lock_ctx(fl, &dispose);

  				added = true;

  			}
  		}

  	}

  	/*

  	 * The above code only modifies existing locks in case of merging or
  	 * replacing. If new lock(s) need to be inserted all modifications are
  	 * done below this, so it's safe yet to bail out.

  	 */
  	error = -ENOLCK; /* "no luck" */
  	if (right && left == right && !new_fl2)
  		goto out;

  	error = 0;
  	if (!added) {

  		if (request->fl_type == F_UNLCK) {
  			if (request->fl_flags & FL_EXISTS)
  				error = -ENOENT;

  			goto out;

  		}

  
  		if (!new_fl) {
  			error = -ENOLCK;
  			goto out;
  		}

  		locks_copy_lock(new_fl, request);

  		locks_insert_lock_ctx(new_fl, &fl->fl_list);

  		fl = new_fl;

  		new_fl = NULL;
  	}
  	if (right) {
  		if (left == right) {
  			/* The new lock breaks the old one in two pieces,
  			 * so we have to use the second new lock.
  			 */
  			left = new_fl2;
  			new_fl2 = NULL;
  			locks_copy_lock(left, right);

  			locks_insert_lock_ctx(left, &fl->fl_list);

  		}
  		right->fl_start = request->fl_end + 1;
  		locks_wake_up_blocks(right);
  	}
  	if (left) {
  		left->fl_end = request->fl_start - 1;
  		locks_wake_up_blocks(left);
  	}
   out:

  	spin_unlock(&ctx->flc_lock);

  	percpu_up_read_preempt_enable(&file_rwsem);

  	/*
  	 * Free any unused locks.
  	 */
  	if (new_fl)
  		locks_free_lock(new_fl);
  	if (new_fl2)
  		locks_free_lock(new_fl2);

  	locks_dispose_list(&dispose);

  	trace_posix_lock_inode(inode, request, error);

  	return error;
  }
  
  /**
   * posix_lock_file - Apply a POSIX-style lock to a file
   * @filp: The file to apply the lock to
   * @fl: The lock to be applied

   * @conflock: Place to return a copy of the conflicting lock, if found.

   *
   * Add a POSIX style lock to a file.
   * We merge adjacent & overlapping locks whenever possible.
   * POSIX locks are sorted by owner task, then by starting address

   *
   * Note that if called with an FL_EXISTS argument, the caller may determine
   * whether or not a lock was successfully freed by testing the return
   * value for -ENOENT.

   */

  int posix_lock_file(struct file *filp, struct file_lock *fl,

  			struct file_lock *conflock)
  {

  	return posix_lock_inode(locks_inode(filp), fl, conflock);

  }

  EXPORT_SYMBOL(posix_lock_file);

  
  /**

   * posix_lock_inode_wait - Apply a POSIX-style lock to a file
   * @inode: inode of file to which lock request should be applied

   * @fl: The lock to be applied
   *

   * Apply a POSIX style lock request to an inode.

   */

  static int posix_lock_inode_wait(struct inode *inode, struct file_lock *fl)

  {
  	int error;
  	might_sleep ();
  	for (;;) {

  		error = posix_lock_inode(inode, fl, NULL);

  		if (error != FILE_LOCK_DEFERRED)

  			break;
  		error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
  		if (!error)
  			continue;
  
  		locks_delete_block(fl);
  		break;
  	}
  	return error;
  }

  #ifdef CONFIG_MANDATORY_FILE_LOCKING

  /**

   * locks_mandatory_locked - Check for an active lock

   * @file: the file to check

   *
   * Searches the inode's list of locks to find any POSIX locks which conflict.
   * This function is called from locks_verify_locked() only.
   */

  int locks_mandatory_locked(struct file *file)

  {

  	int ret;

  	struct inode *inode = locks_inode(file);

  	struct file_lock_context *ctx;

  	struct file_lock *fl;

  	ctx = smp_load_acquire(&inode->i_flctx);

  	if (!ctx || list_empty_careful(&ctx->flc_posix))
  		return 0;

  	/*
  	 * Search the lock list for this inode for any POSIX locks.
  	 */

  	spin_lock(&ctx->flc_lock);

  	ret = 0;
  	list_for_each_entry(fl, &ctx->flc_posix, fl_list) {

  		if (fl->fl_owner != current->files &&

  		    fl->fl_owner != file) {
  			ret = -EAGAIN;

  			break;

  		}

  	}

  	spin_unlock(&ctx->flc_lock);

  	return ret;

  }
  
  /**
   * locks_mandatory_area - Check for a conflicting lock

   * @inode:	the file to check

   * @filp:       how the file was opened (if it was)

   * @start:	first byte in the file to check
   * @end:	lastbyte in the file to check
   * @type:	%F_WRLCK for a write lock, else %F_RDLCK

   *
   * Searches the inode's list of locks to find any POSIX locks which conflict.

   */

  int locks_mandatory_area(struct inode *inode, struct file *filp, loff_t start,
  			 loff_t end, unsigned char type)

  {
  	struct file_lock fl;
  	int error;

  	bool sleep = false;

  
  	locks_init_lock(&fl);

  	fl.fl_pid = current->tgid;
  	fl.fl_file = filp;
  	fl.fl_flags = FL_POSIX | FL_ACCESS;
  	if (filp && !(filp->f_flags & O_NONBLOCK))

  		sleep = true;

  	fl.fl_type = type;
  	fl.fl_start = start;
  	fl.fl_end = end;

  
  	for (;;) {

  		if (filp) {

  			fl.fl_owner = filp;

  			fl.fl_flags &= ~FL_SLEEP;

  			error = posix_lock_inode(inode, &fl, NULL);

  			if (!error)
  				break;
  		}
  
  		if (sleep)
  			fl.fl_flags |= FL_SLEEP;
  		fl.fl_owner = current->files;

  		error = posix_lock_inode(inode, &fl, NULL);

  		if (error != FILE_LOCK_DEFERRED)

  			break;
  		error = wait_event_interruptible(fl.fl_wait, !fl.fl_next);
  		if (!error) {
  			/*
  			 * If we've been sleeping someone might have
  			 * changed the permissions behind our back.
  			 */

  			if (__mandatory_lock(inode))

  				continue;
  		}
  
  		locks_delete_block(&fl);
  		break;
  	}
  
  	return error;
  }
  
  EXPORT_SYMBOL(locks_mandatory_area);

  #endif /* CONFIG_MANDATORY_FILE_LOCKING */

  static void lease_clear_pending(struct file_lock *fl, int arg)
  {
  	switch (arg) {
  	case F_UNLCK:
  		fl->fl_flags &= ~FL_UNLOCK_PENDING;
  		/* fall through: */
  	case F_RDLCK:
  		fl->fl_flags &= ~FL_DOWNGRADE_PENDING;
  	}
  }

  /* We already had a lease on this file; just change its type */

  int lease_modify(struct file_lock *fl, int arg, struct list_head *dispose)

  {

  	int error = assign_type(fl, arg);
  
  	if (error)
  		return error;

  	lease_clear_pending(fl, arg);

  	locks_wake_up_blocks(fl);

  	if (arg == F_UNLCK) {
  		struct file *filp = fl->fl_file;
  
  		f_delown(filp);
  		filp->f_owner.signum = 0;

  		fasync_helper(0, fl->fl_file, 0, &fl->fl_fasync);
  		if (fl->fl_fasync != NULL) {
  			printk(KERN_ERR "locks_delete_lock: fasync == %p
  ", fl->fl_fasync);
  			fl->fl_fasync = NULL;
  		}

  		locks_delete_lock_ctx(fl, dispose);

  	}

  	return 0;
  }

  EXPORT_SYMBOL(lease_modify);

  static bool past_time(unsigned long then)
  {
  	if (!then)
  		/* 0 is a special value meaning "this never expires": */
  		return false;
  	return time_after(jiffies, then);
  }

  static void time_out_leases(struct inode *inode, struct list_head *dispose)

  {

  	struct file_lock_context *ctx = inode->i_flctx;
  	struct file_lock *fl, *tmp;

  	lockdep_assert_held(&ctx->flc_lock);

  	list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list) {

  		trace_time_out_leases(inode, fl);

  		if (past_time(fl->fl_downgrade_time))

  			lease_modify(fl, F_RDLCK, dispose);

  		if (past_time(fl->fl_break_time))

  			lease_modify(fl, F_UNLCK, dispose);

  	}
  }

  static bool leases_conflict(struct file_lock *lease, struct file_lock *breaker)
  {

  	if ((breaker->fl_flags & FL_LAYOUT) != (lease->fl_flags & FL_LAYOUT))
  		return false;

  	if ((breaker->fl_flags & FL_DELEG) && (lease->fl_flags & FL_LEASE))
  		return false;
  	return locks_conflict(breaker, lease);
  }

  static bool
  any_leases_conflict(struct inode *inode, struct file_lock *breaker)
  {

  	struct file_lock_context *ctx = inode->i_flctx;

  	struct file_lock *fl;

  	lockdep_assert_held(&ctx->flc_lock);

  	list_for_each_entry(fl, &ctx->flc_lease, fl_list) {

  		if (leases_conflict(fl, breaker))
  			return true;
  	}
  	return false;
  }

  /**
   *	__break_lease	-	revoke all outstanding leases on file
   *	@inode: the inode of the file to return

   *	@mode: O_RDONLY: break only write leases; O_WRONLY or O_RDWR:
   *	    break all leases
   *	@type: FL_LEASE: break leases and delegations; FL_DELEG: break
   *	    only delegations

   *

   *	break_lease (inlined for speed) has checked there already is at least
   *	some kind of lock (maybe a lease) on this file.  Leases are broken on
   *	a call to open() or truncate().  This function can sleep unless you

   *	specified %O_NONBLOCK to your open().
   */

  int __break_lease(struct inode *inode, unsigned int mode, unsigned int type)

  {

  	int error = 0;

  	struct file_lock_context *ctx;

  	struct file_lock *new_fl, *fl, *tmp;

  	unsigned long break_time;

  	int want_write = (mode & O_ACCMODE) != O_RDONLY;

  	LIST_HEAD(dispose);

  	new_fl = lease_alloc(NULL, want_write ? F_WRLCK : F_RDLCK);

  	if (IS_ERR(new_fl))
  		return PTR_ERR(new_fl);

  	new_fl->fl_flags = type;

  	/* typically we will check that ctx is non-NULL before calling */

  	ctx = smp_load_acquire(&inode->i_flctx);

  	if (!ctx) {
  		WARN_ON_ONCE(1);
  		return error;
  	}

  	percpu_down_read_preempt_disable(&file_rwsem);

  	spin_lock(&ctx->flc_lock);

  	time_out_leases(inode, &dispose);

  	if (!any_leases_conflict(inode, new_fl))

  		goto out;

  	break_time = 0;
  	if (lease_break_time > 0) {
  		break_time = jiffies + lease_break_time * HZ;
  		if (break_time == 0)
  			break_time++;	/* so that 0 means no break time */
  	}

  	list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list) {

  		if (!leases_conflict(fl, new_fl))
  			continue;

  		if (want_write) {
  			if (fl->fl_flags & FL_UNLOCK_PENDING)
  				continue;
  			fl->fl_flags |= FL_UNLOCK_PENDING;

  			fl->fl_break_time = break_time;

  		} else {

  			if (lease_breaking(fl))

  				continue;
  			fl->fl_flags |= FL_DOWNGRADE_PENDING;
  			fl->fl_downgrade_time = break_time;

  		}

  		if (fl->fl_lmops->lm_break(fl))

  			locks_delete_lock_ctx(fl, &dispose);

  	}

  	if (list_empty(&ctx->flc_lease))

  		goto out;

  	if (mode & O_NONBLOCK) {

  		trace_break_lease_noblock(inode, new_fl);

  		error = -EWOULDBLOCK;
  		goto out;
  	}
  
  restart:

  	fl = list_first_entry(&ctx->flc_lease, struct file_lock, fl_list);
  	break_time = fl->fl_break_time;

  	if (break_time != 0)

  		break_time -= jiffies;

  	if (break_time == 0)
  		break_time++;

  	locks_insert_block(fl, new_fl);

  	trace_break_lease_block(inode, new_fl);

  	spin_unlock(&ctx->flc_lock);

  	percpu_up_read_preempt_enable(&file_rwsem);

  	locks_dispose_list(&dispose);

  	error = wait_event_interruptible_timeout(new_fl->fl_wait,
  						!new_fl->fl_next, break_time);

  	percpu_down_read_preempt_disable(&file_rwsem);

  	spin_lock(&ctx->flc_lock);