text: /*
   * linux/ipc/sem.c
   * Copyright (C) 1992 Krishna Balasubramanian
   * Copyright (C) 1995 Eric Schenk, Bruno Haible
   *
   * /proc/sysvipc/sem support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
   *
   * SMP-threaded, sysctl's added
   * (c) 1999 Manfred Spraul <manfred@colorfullife.com>
   * Enforced range limit on SEM_UNDO
   * (c) 2001 Red Hat Inc
   * Lockless wakeup
   * (c) 2003 Manfred Spraul <manfred@colorfullife.com>
   * Further wakeup optimizations, documentation
   * (c) 2010 Manfred Spraul <manfred@colorfullife.com>
   *
   * support for audit of ipc object properties and permission changes
   * Dustin Kirkland <dustin.kirkland@us.ibm.com>
   *
   * namespaces support
   * OpenVZ, SWsoft Inc.
   * Pavel Emelianov <xemul@openvz.org>
   *
   * Implementation notes: (May 2010)
   * This file implements System V semaphores.
   *
   * User space visible behavior:
   * - FIFO ordering for semop() operations (just FIFO, not starvation
   *   protection)
   * - multiple semaphore operations that alter the same semaphore in
   *   one semop() are handled.
   * - sem_ctime (time of last semctl()) is updated in the IPC_SET, SETVAL and
   *   SETALL calls.
   * - two Linux specific semctl() commands: SEM_STAT, SEM_INFO.
   * - undo adjustments at process exit are limited to 0..SEMVMX.
   * - namespace are supported.
   * - SEMMSL, SEMMNS, SEMOPM and SEMMNI can be configured at runtine by writing
   *   to /proc/sys/kernel/sem.
   * - statistics about the usage are reported in /proc/sysvipc/sem.
   *
   * Internals:
   * - scalability:
   *   - all global variables are read-mostly.
   *   - semop() calls and semctl(RMID) are synchronized by RCU.
   *   - most operations do write operations (actually: spin_lock calls) to
   *     the per-semaphore array structure.
   *   Thus: Perfect SMP scaling between independent semaphore arrays.
   *         If multiple semaphores in one array are used, then cache line
   *         trashing on the semaphore array spinlock will limit the scaling.
   * - semncnt and semzcnt are calculated on demand in count_semcnt()
   * - the task that performs a successful semop() scans the list of all
   *   sleeping tasks and completes any pending operations that can be fulfilled.
   *   Semaphores are actively given to waiting tasks (necessary for FIFO).
   *   (see update_queue())
   * - To improve the scalability, the actual wake-up calls are performed after
   *   dropping all locks. (see wake_up_sem_queue_prepare(),
   *   wake_up_sem_queue_do())
   * - All work is done by the waker, the woken up task does not have to do
   *   anything - not even acquiring a lock or dropping a refcount.
   * - A woken up task may not even touch the semaphore array anymore, it may
   *   have been destroyed already by a semctl(RMID).
   * - The synchronizations between wake-ups due to a timeout/signal and a
   *   wake-up due to a completed semaphore operation is achieved by using an
   *   intermediate state (IN_WAKEUP).
   * - UNDO values are stored in an array (one per process and per
   *   semaphore array, lazily allocated). For backwards compatibility, multiple
   *   modes for the UNDO variables are supported (per process, per thread)
   *   (see copy_semundo, CLONE_SYSVSEM)
   * - There are two lists of the pending operations: a per-array list
   *   and per-semaphore list (stored in the array). This allows to achieve FIFO
   *   ordering without always scanning all pending operations.
   *   The worst-case behavior is nevertheless O(N^2) for N wakeups.
   */
  
  #include <linux/slab.h>
  #include <linux/spinlock.h>
  #include <linux/init.h>
  #include <linux/proc_fs.h>
  #include <linux/time.h>
  #include <linux/security.h>
  #include <linux/syscalls.h>
  #include <linux/audit.h>
  #include <linux/capability.h>
  #include <linux/seq_file.h>
  #include <linux/rwsem.h>
  #include <linux/nsproxy.h>
  #include <linux/ipc_namespace.h>
  
  #include <linux/uaccess.h>
  #include "util.h"
  
  /* One semaphore structure for each semaphore in the system. */
  struct sem {
  	int	semval;		/* current value */
  	int	sempid;		/* pid of last operation */
  	spinlock_t	lock;	/* spinlock for fine-grained semtimedop */
  	struct list_head pending_alter; /* pending single-sop operations */
  					/* that alter the semaphore */
  	struct list_head pending_const; /* pending single-sop operations */
  					/* that do not alter the semaphore*/
  	time_t	sem_otime;	/* candidate for sem_otime */
  } ____cacheline_aligned_in_smp;
  
  /* One queue for each sleeping process in the system. */
  struct sem_queue {
  	struct list_head	list;	 /* queue of pending operations */
  	struct task_struct	*sleeper; /* this process */
  	struct sem_undo		*undo;	 /* undo structure */
  	int			pid;	 /* process id of requesting process */
  	int			status;	 /* completion status of operation */
  	struct sembuf		*sops;	 /* array of pending operations */
  	struct sembuf		*blocking; /* the operation that blocked */
  	int			nsops;	 /* number of operations */
  	int			alter;	 /* does *sops alter the array? */
  };
  
  /* Each task has a list of undo requests. They are executed automatically
   * when the process exits.
   */
  struct sem_undo {
  	struct list_head	list_proc;	/* per-process list: *
  						 * all undos from one process
  						 * rcu protected */
  	struct rcu_head		rcu;		/* rcu struct for sem_undo */
  	struct sem_undo_list	*ulp;		/* back ptr to sem_undo_list */
  	struct list_head	list_id;	/* per semaphore array list:
  						 * all undos for one array */
  	int			semid;		/* semaphore set identifier */
  	short			*semadj;	/* array of adjustments */
  						/* one per semaphore */
  };
  
  /* sem_undo_list controls shared access to the list of sem_undo structures
   * that may be shared among all a CLONE_SYSVSEM task group.
   */
  struct sem_undo_list {
  	atomic_t		refcnt;
  	spinlock_t		lock;
  	struct list_head	list_proc;
  };
  
  
  #define sem_ids(ns)	((ns)->ids[IPC_SEM_IDS])
  
  #define sem_checkid(sma, semid)	ipc_checkid(&sma->sem_perm, semid)
  
  static int newary(struct ipc_namespace *, struct ipc_params *);
  static void freeary(struct ipc_namespace *, struct kern_ipc_perm *);
  #ifdef CONFIG_PROC_FS
  static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
  #endif
  
  #define SEMMSL_FAST	256 /* 512 bytes on stack */
  #define SEMOPM_FAST	64  /* ~ 372 bytes on stack */
  
  /*
   * Locking:
   *	sem_undo.id_next,
   *	sem_array.complex_count,
   *	sem_array.pending{_alter,_cont},
   *	sem_array.sem_undo: global sem_lock() for read/write
   *	sem_undo.proc_next: only "current" is allowed to read/write that field.
   *
   *	sem_array.sem_base[i].pending_{const,alter}:
   *		global or semaphore sem_lock() for read/write
   */
  
  #define sc_semmsl	sem_ctls[0]
  #define sc_semmns	sem_ctls[1]
  #define sc_semopm	sem_ctls[2]
  #define sc_semmni	sem_ctls[3]
  
  void sem_init_ns(struct ipc_namespace *ns)
  {
  	ns->sc_semmsl = SEMMSL;
  	ns->sc_semmns = SEMMNS;
  	ns->sc_semopm = SEMOPM;
  	ns->sc_semmni = SEMMNI;
  	ns->used_sems = 0;
  	ipc_init_ids(&ns->ids[IPC_SEM_IDS]);
  }
  
  #ifdef CONFIG_IPC_NS
  void sem_exit_ns(struct ipc_namespace *ns)
  {
  	free_ipcs(ns, &sem_ids(ns), freeary);
  	idr_destroy(&ns->ids[IPC_SEM_IDS].ipcs_idr);
  }
  #endif
  
  void __init sem_init(void)
  {
  	sem_init_ns(&init_ipc_ns);
  	ipc_init_proc_interface("sysvipc/sem",
  				"       key      semid perms      nsems   uid   gid  cuid  cgid      otime      ctime\n",
  				IPC_SEM_IDS, sysvipc_sem_proc_show);
  }
  
  /**
   * unmerge_queues - unmerge queues, if possible.
   * @sma: semaphore array
   *
   * The function unmerges the wait queues if complex_count is 0.
   * It must be called prior to dropping the global semaphore array lock.
   */
  static void unmerge_queues(struct sem_array *sma)
  {
  	struct sem_queue *q, *tq;
  
  	/* complex operations still around? */
  	if (sma->complex_count)
  		return;
  	/*
  	 * We will switch back to simple mode.
  	 * Move all pending operation back into the per-semaphore
  	 * queues.
  	 */
  	list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
  		struct sem *curr;
  		curr = &sma->sem_base[q->sops[0].sem_num];
  
  		list_add_tail(&q->list, &curr->pending_alter);
  	}
  	INIT_LIST_HEAD(&sma->pending_alter);
  }
  
  /**
   * merge_queues - merge single semop queues into global queue
   * @sma: semaphore array
   *
   * This function merges all per-semaphore queues into the global queue.
   * It is necessary to achieve FIFO ordering for the pending single-sop
   * operations when a multi-semop operation must sleep.
   * Only the alter operations must be moved, the const operations can stay.
   */
  static void merge_queues(struct sem_array *sma)
  {
  	int i;
  	for (i = 0; i < sma->sem_nsems; i++) {
  		struct sem *sem = sma->sem_base + i;
  
  		list_splice_init(&sem->pending_alter, &sma->pending_alter);
  	}
  }
  
  static void sem_rcu_free(struct rcu_head *head)
  {
  	struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
  	struct sem_array *sma = ipc_rcu_to_struct(p);
  
  	security_sem_free(sma);
  	ipc_rcu_free(head);
  }
  
  /*
   * spin_unlock_wait() and !spin_is_locked() are not memory barriers, they
   * are only control barriers.
   * The code must pair with spin_unlock(&sem->lock) or
   * spin_unlock(&sem_perm.lock), thus just the control barrier is insufficient.
   *
   * smp_rmb() is sufficient, as writes cannot pass the control barrier.
   */
  #define ipc_smp_acquire__after_spin_is_unlocked()	smp_rmb()
  
  /*
   * Wait until all currently ongoing simple ops have completed.
   * Caller must own sem_perm.lock.
   * New simple ops cannot start, because simple ops first check
   * that sem_perm.lock is free.
   * that a) sem_perm.lock is free and b) complex_count is 0.
   */
  static void sem_wait_array(struct sem_array *sma)
  {
  	int i;
  	struct sem *sem;
  
  	if (sma->complex_count)  {
  		/* The thread that increased sma->complex_count waited on
  		 * all sem->lock locks. Thus we don't need to wait again.
  		 */
  		return;
  	}
  
  	for (i = 0; i < sma->sem_nsems; i++) {
  		sem = sma->sem_base + i;
  		spin_unlock_wait(&sem->lock);
  	}
  	ipc_smp_acquire__after_spin_is_unlocked();
  }
  
  /*
   * If the request contains only one semaphore operation, and there are
   * no complex transactions pending, lock only the semaphore involved.
   * Otherwise, lock the entire semaphore array, since we either have
   * multiple semaphores in our own semops, or we need to look at
   * semaphores from other pending complex operations.
   */
  static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
  			      int nsops)
  {
  	struct sem *sem;
  
  	if (nsops != 1) {
  		/* Complex operation - acquire a full lock */
  		ipc_lock_object(&sma->sem_perm);
  
  		/* And wait until all simple ops that are processed
  		 * right now have dropped their locks.
  		 */
  		sem_wait_array(sma);
  		return -1;
  	}
  
  	/*
  	 * Only one semaphore affected - try to optimize locking.
  	 * The rules are:
  	 * - optimized locking is possible if no complex operation
  	 *   is either enqueued or processed right now.
  	 * - The test for enqueued complex ops is simple:
  	 *      sma->complex_count != 0
  	 * - Testing for complex ops that are processed right now is
  	 *   a bit more difficult. Complex ops acquire the full lock
  	 *   and first wait that the running simple ops have completed.
  	 *   (see above)
  	 *   Thus: If we own a simple lock and the global lock is free
  	 *	and complex_count is now 0, then it will stay 0 and
  	 *	thus just locking sem->lock is sufficient.
  	 */
  	sem = sma->sem_base + sops->sem_num;
  
  	if (sma->complex_count == 0) {
  		/*
  		 * It appears that no complex operation is around.
  		 * Acquire the per-semaphore lock.
  		 */
  		spin_lock(&sem->lock);
  
  		/* Then check that the global lock is free */
  		if (!spin_is_locked(&sma->sem_perm.lock)) {
  			/*
  			 * We need a memory barrier with acquire semantics,
  			 * otherwise we can race with another thread that does:
  			 *	complex_count++;
  			 *	spin_unlock(sem_perm.lock);
  			 */
  			ipc_smp_acquire__after_spin_is_unlocked();
  
  			/*
  			 * Now repeat the test of complex_count:
  			 * It can't change anymore until we drop sem->lock.
  			 * Thus: if is now 0, then it will stay 0.
  			 */
  			if (sma->complex_count == 0) {
  				/* fast path successful! */
  				return sops->sem_num;
  			}
  		}
  		spin_unlock(&sem->lock);
  	}
  
  	/* slow path: acquire the full lock */
  	ipc_lock_object(&sma->sem_perm);
  
  	if (sma->complex_count == 0) {
  		/* False alarm:
  		 * There is no complex operation, thus we can switch
  		 * back to the fast path.
  		 */
  		spin_lock(&sem->lock);
  		ipc_unlock_object(&sma->sem_perm);
  		return sops->sem_num;
  	} else {
  		/* Not a false alarm, thus complete the sequence for a
  		 * full lock.
  		 */
  		sem_wait_array(sma);
  		return -1;
  	}
  }
  
  static inline void sem_unlock(struct sem_array *sma, int locknum)
  {
  	if (locknum == -1) {
  		unmerge_queues(sma);
  		ipc_unlock_object(&sma->sem_perm);
  	} else {
  		struct sem *sem = sma->sem_base + locknum;
  		spin_unlock(&sem->lock);
  	}
  }
  
  /*
   * sem_lock_(check_) routines are called in the paths where the rwsem
   * is not held.
   *
   * The caller holds the RCU read lock.
   */
  static inline struct sem_array *sem_obtain_lock(struct ipc_namespace *ns,
  			int id, struct sembuf *sops, int nsops, int *locknum)
  {
  	struct kern_ipc_perm *ipcp;
  	struct sem_array *sma;
  
  	ipcp = ipc_obtain_object_idr(&sem_ids(ns), id);
  	if (IS_ERR(ipcp))
  		return ERR_CAST(ipcp);
  
  	sma = container_of(ipcp, struct sem_array, sem_perm);
  	*locknum = sem_lock(sma, sops, nsops);
  
  	/* ipc_rmid() may have already freed the ID while sem_lock
  	 * was spinning: verify that the structure is still valid
  	 */
  	if (ipc_valid_object(ipcp))
  		return container_of(ipcp, struct sem_array, sem_perm);
  
  	sem_unlock(sma, *locknum);
  	return ERR_PTR(-EINVAL);
  }
  
  static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id)
  {
  	struct kern_ipc_perm *ipcp = ipc_obtain_object_idr(&sem_ids(ns), id);
  
  	if (IS_ERR(ipcp))
  		return ERR_CAST(ipcp);
  
  	return container_of(ipcp, struct sem_array, sem_perm);
  }
  
  static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns,
  							int id)
  {
  	struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&sem_ids(ns), id);
  
  	if (IS_ERR(ipcp))
  		return ERR_CAST(ipcp);
  
  	return container_of(ipcp, struct sem_array, sem_perm);
  }
  
  static inline void sem_lock_and_putref(struct sem_array *sma)
  {
  	sem_lock(sma, NULL, -1);
  	ipc_rcu_putref(sma, ipc_rcu_free);
  }
  
  static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
  {
  	ipc_rmid(&sem_ids(ns), &s->sem_perm);
  }
  
  /*
   * Lockless wakeup algorithm:
   * Without the check/retry algorithm a lockless wakeup is possible:
   * - queue.status is initialized to -EINTR before blocking.
   * - wakeup is performed by
   *	* unlinking the queue entry from the pending list
   *	* setting queue.status to IN_WAKEUP
   *	  This is the notification for the blocked thread that a
   *	  result value is imminent.
   *	* call wake_up_process
   *	* set queue.status to the final value.
   * - the previously blocked thread checks queue.status:
   *	* if it's IN_WAKEUP, then it must wait until the value changes
   *	* if it's not -EINTR, then the operation was completed by
   *	  update_queue. semtimedop can return queue.status without
   *	  performing any operation on the sem array.
   *	* otherwise it must acquire the spinlock and check what's up.
   *
   * The two-stage algorithm is necessary to protect against the following
   * races:
   * - if queue.status is set after wake_up_process, then the woken up idle
   *   thread could race forward and try (and fail) to acquire sma->lock
   *   before update_queue had a chance to set queue.status
   * - if queue.status is written before wake_up_process and if the
   *   blocked process is woken up by a signal between writing
   *   queue.status and the wake_up_process, then the woken up
   *   process could return from semtimedop and die by calling
   *   sys_exit before wake_up_process is called. Then wake_up_process
   *   will oops, because the task structure is already invalid.
   *   (yes, this happened on s390 with sysv msg).
   *
   */
  #define IN_WAKEUP	1
  
  /**
   * newary - Create a new semaphore set
   * @ns: namespace
   * @params: ptr to the structure that contains key, semflg and nsems
   *
   * Called with sem_ids.rwsem held (as a writer)
   */
  static int newary(struct ipc_namespace *ns, struct ipc_params *params)
  {
  	int id;
  	int retval;
  	struct sem_array *sma;
  	int size;
  	key_t key = params->key;
  	int nsems = params->u.nsems;
  	int semflg = params->flg;
  	int i;
  
  	if (!nsems)
  		return -EINVAL;
  	if (ns->used_sems + nsems > ns->sc_semmns)
  		return -ENOSPC;
  
  	size = sizeof(*sma) + nsems * sizeof(struct sem);
  	sma = ipc_rcu_alloc(size);
  	if (!sma)
  		return -ENOMEM;
  
  	memset(sma, 0, size);
  
  	sma->sem_perm.mode = (semflg & S_IRWXUGO);
  	sma->sem_perm.key = key;
  
  	sma->sem_perm.security = NULL;
  	retval = security_sem_alloc(sma);
  	if (retval) {
  		ipc_rcu_putref(sma, ipc_rcu_free);
  		return retval;
  	}
  
  	sma->sem_base = (struct sem *) &sma[1];
  
  	for (i = 0; i < nsems; i++) {
  		INIT_LIST_HEAD(&sma->sem_base[i].pending_alter);
  		INIT_LIST_HEAD(&sma->sem_base[i].pending_const);
  		spin_lock_init(&sma->sem_base[i].lock);
  	}
  
  	sma->complex_count = 0;
  	INIT_LIST_HEAD(&sma->pending_alter);
  	INIT_LIST_HEAD(&sma->pending_const);
  	INIT_LIST_HEAD(&sma->list_id);
  	sma->sem_nsems = nsems;
  	sma->sem_ctime = get_seconds();
  
  	id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
  	if (id < 0) {
  		ipc_rcu_putref(sma, sem_rcu_free);
  		return id;
  	}
  	ns->used_sems += nsems;
  
  	sem_unlock(sma, -1);
  	rcu_read_unlock();
  
  	return sma->sem_perm.id;
  }
  
  
  /*
   * Called with sem_ids.rwsem and ipcp locked.
   */
  static inline int sem_security(struct kern_ipc_perm *ipcp, int semflg)
  {
  	struct sem_array *sma;
  
  	sma = container_of(ipcp, struct sem_array, sem_perm);
  	return security_sem_associate(sma, semflg);
  }
  
  /*
   * Called with sem_ids.rwsem and ipcp locked.
   */
  static inline int sem_more_checks(struct kern_ipc_perm *ipcp,
  				struct ipc_params *params)
  {
  	struct sem_array *sma;
  
  	sma = container_of(ipcp, struct sem_array, sem_perm);
  	if (params->u.nsems > sma->sem_nsems)
  		return -EINVAL;
  
  	return 0;
  }
  
  SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
  {
  	struct ipc_namespace *ns;
  	static const struct ipc_ops sem_ops = {
  		.getnew = newary,
  		.associate = sem_security,
  		.more_checks = sem_more_checks,
  	};
  	struct ipc_params sem_params;
  
  	ns = current->nsproxy->ipc_ns;
  
  	if (nsems < 0 || nsems > ns->sc_semmsl)
  		return -EINVAL;
  
  	sem_params.key = key;
  	sem_params.flg = semflg;
  	sem_params.u.nsems = nsems;
  
  	return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
  }
  
  /**
   * perform_atomic_semop - Perform (if possible) a semaphore operation
   * @sma: semaphore array
   * @q: struct sem_queue that describes the operation
   *
   * Returns 0 if the operation was possible.
   * Returns 1 if the operation is impossible, the caller must sleep.
   * Negative values are error codes.
   */
  static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
  {
  	int result, sem_op, nsops, pid;
  	struct sembuf *sop;
  	struct sem *curr;
  	struct sembuf *sops;
  	struct sem_undo *un;
  
  	sops = q->sops;
  	nsops = q->nsops;
  	un = q->undo;
  
  	for (sop = sops; sop < sops + nsops; sop++) {
  		curr = sma->sem_base + sop->sem_num;
  		sem_op = sop->sem_op;
  		result = curr->semval;
  
  		if (!sem_op && result)
  			goto would_block;
  
  		result += sem_op;
  		if (result < 0)
  			goto would_block;
  		if (result > SEMVMX)
  			goto out_of_range;
  
  		if (sop->sem_flg & SEM_UNDO) {
  			int undo = un->semadj[sop->sem_num] - sem_op;
  			/* Exceeding the undo range is an error. */
  			if (undo < (-SEMAEM - 1) || undo > SEMAEM)
  				goto out_of_range;
  			un->semadj[sop->sem_num] = undo;
  		}
  
  		curr->semval = result;
  	}
  
  	sop--;
  	pid = q->pid;
  	while (sop >= sops) {
  		sma->sem_base[sop->sem_num].sempid = pid;
  		sop--;
  	}
  
  	return 0;
  
  out_of_range:
  	result = -ERANGE;
  	goto undo;
  
  would_block:
  	q->blocking = sop;
  
  	if (sop->sem_flg & IPC_NOWAIT)
  		result = -EAGAIN;
  	else
  		result = 1;
  
  undo:
  	sop--;
  	while (sop >= sops) {
  		sem_op = sop->sem_op;
  		sma->sem_base[sop->sem_num].semval -= sem_op;
  		if (sop->sem_flg & SEM_UNDO)
  			un->semadj[sop->sem_num] += sem_op;
  		sop--;
  	}
  
  	return result;
  }
  
  /** wake_up_sem_queue_prepare(q, error): Prepare wake-up
   * @q: queue entry that must be signaled
   * @error: Error value for the signal
   *
   * Prepare the wake-up of the queue entry q.
   */
  static void wake_up_sem_queue_prepare(struct list_head *pt,
  				struct sem_queue *q, int error)
  {
  	if (list_empty(pt)) {
  		/*
  		 * Hold preempt off so that we don't get preempted and have the
  		 * wakee busy-wait until we're scheduled back on.
  		 */
  		preempt_disable();
  	}
  	q->status = IN_WAKEUP;
  	q->pid = error;
  
  	list_add_tail(&q->list, pt);
  }
  
  /**
   * wake_up_sem_queue_do - do the actual wake-up
   * @pt: list of tasks to be woken up
   *
   * Do the actual wake-up.
   * The function is called without any locks held, thus the semaphore array
   * could be destroyed already and the tasks can disappear as soon as the
   * status is set to the actual return code.
   */
  static void wake_up_sem_queue_do(struct list_head *pt)
  {
  	struct sem_queue *q, *t;
  	int did_something;
  
  	did_something = !list_empty(pt);
  	list_for_each_entry_safe(q, t, pt, list) {
  		wake_up_process(q->sleeper);
  		/* q can disappear immediately after writing q->status. */
  		smp_wmb();
  		q->status = q->pid;
  	}
  	if (did_something)
  		preempt_enable();
  }
  
  static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
  {
  	list_del(&q->list);
  	if (q->nsops > 1)
  		sma->complex_count--;
  }
  
  /** check_restart(sma, q)
   * @sma: semaphore array
   * @q: the operation that just completed
   *
   * update_queue is O(N^2) when it restarts scanning the whole queue of
   * waiting operations. Therefore this function checks if the restart is
   * really necessary. It is called after a previously waiting operation
   * modified the array.
   * Note that wait-for-zero operations are handled without restart.
   */
  static int check_restart(struct sem_array *sma, struct sem_queue *q)
  {
  	/* pending complex alter operations are too difficult to analyse */
  	if (!list_empty(&sma->pending_alter))
  		return 1;
  
  	/* we were a sleeping complex operation. Too difficult */
  	if (q->nsops > 1)
  		return 1;
  
  	/* It is impossible that someone waits for the new value:
  	 * - complex operations always restart.
  	 * - wait-for-zero are handled seperately.
  	 * - q is a previously sleeping simple operation that
  	 *   altered the array. It must be a decrement, because
  	 *   simple increments never sleep.
  	 * - If there are older (higher priority) decrements
  	 *   in the queue, then they have observed the original
  	 *   semval value and couldn't proceed. The operation
  	 *   decremented to value - thus they won't proceed either.
  	 */
  	return 0;
  }
  
  /**
   * wake_const_ops - wake up non-alter tasks
   * @sma: semaphore array.
   * @semnum: semaphore that was modified.
   * @pt: list head for the tasks that must be woken up.
   *
   * wake_const_ops must be called after a semaphore in a semaphore array
   * was set to 0. If complex const operations are pending, wake_const_ops must
   * be called with semnum = -1, as well as with the number of each modified
   * semaphore.
   * The tasks that must be woken up are added to @pt. The return code
   * is stored in q->pid.
   * The function returns 1 if at least one operation was completed successfully.
   */
  static int wake_const_ops(struct sem_array *sma, int semnum,
  				struct list_head *pt)
  {
  	struct sem_queue *q;
  	struct list_head *walk;
  	struct list_head *pending_list;
  	int semop_completed = 0;
  
  	if (semnum == -1)
  		pending_list = &sma->pending_const;
  	else
  		pending_list = &sma->sem_base[semnum].pending_const;
  
  	walk = pending_list->next;
  	while (walk != pending_list) {
  		int error;
  
  		q = container_of(walk, struct sem_queue, list);
  		walk = walk->next;
  
  		error = perform_atomic_semop(sma, q);
  
  		if (error <= 0) {
  			/* operation completed, remove from queue & wakeup */
  
  			unlink_queue(sma, q);
  
  			wake_up_sem_queue_prepare(pt, q, error);
  			if (error == 0)
  				semop_completed = 1;
  		}
  	}
  	return semop_completed;
  }
  
  /**
   * do_smart_wakeup_zero - wakeup all wait for zero tasks
   * @sma: semaphore array
   * @sops: operations that were performed
   * @nsops: number of operations
   * @pt: list head of the tasks that must be woken up.
   *
   * Checks all required queue for wait-for-zero operations, based
   * on the actual changes that were performed on the semaphore array.
   * The function returns 1 if at least one operation was completed successfully.
   */
  static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops,
  					int nsops, struct list_head *pt)
  {
  	int i;
  	int semop_completed = 0;
  	int got_zero = 0;
  
  	/* first: the per-semaphore queues, if known */
  	if (sops) {
  		for (i = 0; i < nsops; i++) {
  			int num = sops[i].sem_num;
  
  			if (sma->sem_base[num].semval == 0) {
  				got_zero = 1;
  				semop_completed |= wake_const_ops(sma, num, pt);
  			}
  		}
  	} else {
  		/*
  		 * No sops means modified semaphores not known.
  		 * Assume all were changed.
  		 */
  		for (i = 0; i < sma->sem_nsems; i++) {
  			if (sma->sem_base[i].semval == 0) {
  				got_zero = 1;
  				semop_completed |= wake_const_ops(sma, i, pt);
  			}
  		}
  	}
  	/*
  	 * If one of the modified semaphores got 0,
  	 * then check the global queue, too.
  	 */
  	if (got_zero)
  		semop_completed |= wake_const_ops(sma, -1, pt);
  
  	return semop_completed;
  }
  
  
  /**
   * update_queue - look for tasks that can be completed.
   * @sma: semaphore array.
   * @semnum: semaphore that was modified.
   * @pt: list head for the tasks that must be woken up.
   *
   * update_queue must be called after a semaphore in a semaphore array
   * was modified. If multiple semaphores were modified, update_queue must
   * be called with semnum = -1, as well as with the number of each modified
   * semaphore.
   * The tasks that must be woken up are added to @pt. The return code
   * is stored in q->pid.
   * The function internally checks if const operations can now succeed.
   *
   * The function return 1 if at least one semop was completed successfully.
   */
  static int update_queue(struct sem_array *sma, int semnum, struct list_head *pt)
  {
  	struct sem_queue *q;
  	struct list_head *walk;
  	struct list_head *pending_list;
  	int semop_completed = 0;
  
  	if (semnum == -1)
  		pending_list = &sma->pending_alter;
  	else
  		pending_list = &sma->sem_base[semnum].pending_alter;
  
  again:
  	walk = pending_list->next;
  	while (walk != pending_list) {
  		int error, restart;
  
  		q = container_of(walk, struct sem_queue, list);
  		walk = walk->next;
  
  		/* If we are scanning the single sop, per-semaphore list of
  		 * one semaphore and that semaphore is 0, then it is not
  		 * necessary to scan further: simple increments
  		 * that affect only one entry succeed immediately and cannot
  		 * be in the  per semaphore pending queue, and decrements
  		 * cannot be successful if the value is already 0.
  		 */
  		if (semnum != -1 && sma->sem_base[semnum].semval == 0)
  			break;
  
  		error = perform_atomic_semop(sma, q);
  
  		/* Does q->sleeper still need to sleep? */
  		if (error > 0)
  			continue;
  
  		unlink_queue(sma, q);
  
  		if (error) {
  			restart = 0;
  		} else {
  			semop_completed = 1;
  			do_smart_wakeup_zero(sma, q->sops, q->nsops, pt);
  			restart = check_restart(sma, q);
  		}
  
  		wake_up_sem_queue_prepare(pt, q, error);
  		if (restart)
  			goto again;
  	}
  	return semop_completed;
  }
  
  /**
   * set_semotime - set sem_otime
   * @sma: semaphore array
   * @sops: operations that modified the array, may be NULL
   *
   * sem_otime is replicated to avoid cache line trashing.
   * This function sets one instance to the current time.
   */
  static void set_semotime(struct sem_array *sma, struct sembuf *sops)
  {
  	if (sops == NULL) {
  		sma->sem_base[0].sem_otime = get_seconds();
  	} else {
  		sma->sem_base[sops[0].sem_num].sem_otime =
  							get_seconds();
  	}
  }
  
  /**
   * do_smart_update - optimized update_queue
   * @sma: semaphore array
   * @sops: operations that were performed
   * @nsops: number of operations
   * @otime: force setting otime
   * @pt: list head of the tasks that must be woken up.
   *
   * do_smart_update() does the required calls to update_queue and wakeup_zero,
   * based on the actual changes that were performed on the semaphore array.
   * Note that the function does not do the actual wake-up: the caller is
   * responsible for calling wake_up_sem_queue_do(@pt).
   * It is safe to perform this call after dropping all locks.
   */
  static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops,
  			int otime, struct list_head *pt)
  {
  	int i;
  
  	otime |= do_smart_wakeup_zero(sma, sops, nsops, pt);
  
  	if (!list_empty(&sma->pending_alter)) {
  		/* semaphore array uses the global queue - just process it. */
  		otime |= update_queue(sma, -1, pt);
  	} else {
  		if (!sops) {
  			/*
  			 * No sops, thus the modified semaphores are not
  			 * known. Check all.
  			 */
  			for (i = 0; i < sma->sem_nsems; i++)
  				otime |= update_queue(sma, i, pt);
  		} else {
  			/*
  			 * Check the semaphores that were increased:
  			 * - No complex ops, thus all sleeping ops are
  			 *   decrease.
  			 * - if we decreased the value, then any sleeping
  			 *   semaphore ops wont be able to run: If the
  			 *   previous value was too small, then the new
  			 *   value will be too small, too.
  			 */
  			for (i = 0; i < nsops; i++) {
  				if (sops[i].sem_op > 0) {
  					otime |= update_queue(sma,
  							sops[i].sem_num, pt);
  				}
  			}
  		}
  	}
  	if (otime)
  		set_semotime(sma, sops);
  }
  
  /*
   * check_qop: Test if a queued operation sleeps on the semaphore semnum
   */
  static int check_qop(struct sem_array *sma, int semnum, struct sem_queue *q,
  			bool count_zero)
  {
  	struct sembuf *sop = q->blocking;
  
  	/*
  	 * Linux always (since 0.99.10) reported a task as sleeping on all
  	 * semaphores. This violates SUS, therefore it was changed to the
  	 * standard compliant behavior.
  	 * Give the administrators a chance to notice that an application
  	 * might misbehave because it relies on the Linux behavior.
  	 */
  	pr_info_once("semctl(GETNCNT/GETZCNT) is since 3.16 Single Unix Specification compliant.\n"
  			"The task %s (%d) triggered the difference, watch for misbehavior.\n",
  			current->comm, task_pid_nr(current));
  
  	if (sop->sem_num != semnum)
  		return 0;
  
  	if (count_zero && sop->sem_op == 0)
  		return 1;
  	if (!count_zero && sop->sem_op < 0)
  		return 1;
  
  	return 0;
  }
  
  /* The following counts are associated to each semaphore:
   *   semncnt        number of tasks waiting on semval being nonzero
   *   semzcnt        number of tasks waiting on semval being zero
   *
   * Per definition, a task waits only on the semaphore of the first semop
   * that cannot proceed, even if additional operation would block, too.
   */
  static int count_semcnt(struct sem_array *sma, ushort semnum,
  			bool count_zero)
  {
  	struct list_head *l;
  	struct sem_queue *q;
  	int semcnt;
  
  	semcnt = 0;
  	/* First: check the simple operations. They are easy to evaluate */
  	if (count_zero)
  		l = &sma->sem_base[semnum].pending_const;
  	else
  		l = &sma->sem_base[semnum].pending_alter;
  
  	list_for_each_entry(q, l, list) {
  		/* all task on a per-semaphore list sleep on exactly
  		 * that semaphore
  		 */
  		semcnt++;
  	}
  
  	/* Then: check the complex operations. */
  	list_for_each_entry(q, &sma->pending_alter, list) {
  		semcnt += check_qop(sma, semnum, q, count_zero);
  	}
  	if (count_zero) {
  		list_for_each_entry(q, &sma->pending_const, list) {
  			semcnt += check_qop(sma, semnum, q, count_zero);
  		}
  	}
  	return semcnt;
  }
  
  /* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
   * as a writer and the spinlock for this semaphore set hold. sem_ids.rwsem
   * remains locked on exit.
   */
  static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
  {
  	struct sem_undo *un, *tu;
  	struct sem_queue *q, *tq;
  	struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
  	struct list_head tasks;
  	int i;
  
  	/* Free the existing undo structures for this semaphore set.  */
  	ipc_assert_locked_object(&sma->sem_perm);
  	list_for_each_entry_safe(un, tu, &sma->list_id, list_id) {
  		list_del(&un->list_id);
  		spin_lock(&un->ulp->lock);
  		un->semid = -1;
  		list_del_rcu(&un->list_proc);
  		spin_unlock(&un->ulp->lock);
  		kfree_rcu(un, rcu);
  	}
  
  	/* Wake up all pending processes and let them fail with EIDRM. */
  	INIT_LIST_HEAD(&tasks);
  	list_for_each_entry_safe(q, tq, &sma->pending_const, list) {
  		unlink_queue(sma, q);
  		wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
  	}
  
  	list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
  		unlink_queue(sma, q);
  		wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
  	}
  	for (i = 0; i < sma->sem_nsems; i++) {
  		struct sem *sem = sma->sem_base + i;
  		list_for_each_entry_safe(q, tq, &sem->pending_const, list) {
  			unlink_queue(sma, q);
  			wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
  		}
  		list_for_each_entry_safe(q, tq, &sem->pending_alter, list) {
  			unlink_queue(sma, q);
  			wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
  		}
  	}
  
  	/* Remove the semaphore set from the IDR */
  	sem_rmid(ns, sma);
  	sem_unlock(sma, -1);
  	rcu_read_unlock();
  
  	wake_up_sem_queue_do(&tasks);
  	ns->used_sems -= sma->sem_nsems;
  	ipc_rcu_putref(sma, sem_rcu_free);
  }
  
  static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version)
  {
  	switch (version) {
  	case IPC_64:
  		return copy_to_user(buf, in, sizeof(*in));
  	case IPC_OLD:
  	    {
  		struct semid_ds out;
  
  		memset(&out, 0, sizeof(out));
  
  		ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm);
  
  		out.sem_otime	= in->sem_otime;
  		out.sem_ctime	= in->sem_ctime;
  		out.sem_nsems	= in->sem_nsems;
  
  		return copy_to_user(buf, &out, sizeof(out));
  	    }
  	default:
  		return -EINVAL;
  	}
  }
  
  static time_t get_semotime(struct sem_array *sma)
  {
  	int i;
  	time_t res;
  
  	res = sma->sem_base[0].sem_otime;
  	for (i = 1; i < sma->sem_nsems; i++) {
  		time_t to = sma->sem_base[i].sem_otime;
  
  		if (to > res)
  			res = to;
  	}
  	return res;
  }
  
  static int semctl_nolock(struct ipc_namespace *ns, int semid,
  			 int cmd, int version, void __user *p)
  {
  	int err;
  	struct sem_array *sma;
  
  	switch (cmd) {
  	case IPC_INFO:
  	case SEM_INFO:
  	{
  		struct seminfo seminfo;
  		int max_id;
  
  		err = security_sem_semctl(NULL, cmd);
  		if (err)
  			return err;
  
  		memset(&seminfo, 0, sizeof(seminfo));
  		seminfo.semmni = ns->sc_semmni;
  		seminfo.semmns = ns->sc_semmns;
  		seminfo.semmsl = ns->sc_semmsl;
  		seminfo.semopm = ns->sc_semopm;
  		seminfo.semvmx = SEMVMX;
  		seminfo.semmnu = SEMMNU;
  		seminfo.semmap = SEMMAP;
  		seminfo.semume = SEMUME;
  		down_read(&sem_ids(ns).rwsem);
  		if (cmd == SEM_INFO) {
  			seminfo.semusz = sem_ids(ns).in_use;
  			seminfo.semaem = ns->used_sems;
  		} else {
  			seminfo.semusz = SEMUSZ;
  			seminfo.semaem = SEMAEM;
  		}
  		max_id = ipc_get_maxid(&sem_ids(ns));
  		up_read(&sem_ids(ns).rwsem);
  		if (copy_to_user(p, &seminfo, sizeof(struct seminfo)))
  			return -EFAULT;
  		return (max_id < 0) ? 0 : max_id;
  	}
  	case IPC_STAT:
  	case SEM_STAT:
  	{
  		struct semid64_ds tbuf;
  		int id = 0;
  
  		memset(&tbuf, 0, sizeof(tbuf));
  
  		rcu_read_lock();
  		if (cmd == SEM_STAT) {
  			sma = sem_obtain_object(ns, semid);
  			if (IS_ERR(sma)) {
  				err = PTR_ERR(sma);
  				goto out_unlock;
  			}
  			id = sma->sem_perm.id;
  		} else {
  			sma = sem_obtain_object_check(ns, semid);
  			if (IS_ERR(sma)) {
  				err = PTR_ERR(sma);
  				goto out_unlock;
  			}
  		}
  
  		err = -EACCES;
  		if (ipcperms(ns, &sma->sem_perm, S_IRUGO))
  			goto out_unlock;
  
  		err = security_sem_semctl(sma, cmd);
  		if (err)
  			goto out_unlock;
  
  		kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
  		tbuf.sem_otime = get_semotime(sma);
  		tbuf.sem_ctime = sma->sem_ctime;
  		tbuf.sem_nsems = sma->sem_nsems;
  		rcu_read_unlock();
  		if (copy_semid_to_user(p, &tbuf, version))
  			return -EFAULT;
  		return id;
  	}
  	default:
  		return -EINVAL;
  	}
  out_unlock:
  	rcu_read_unlock();
  	return err;
  }
  
  static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
  		unsigned long arg)
  {
  	struct sem_undo *un;
  	struct sem_array *sma;
  	struct sem *curr;
  	int err;
  	struct list_head tasks;
  	int val;
  #if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)
  	/* big-endian 64bit */
  	val = arg >> 32;
  #else
  	/* 32bit or little-endian 64bit */
  	val = arg;
  #endif
  
  	if (val > SEMVMX || val < 0)
  		return -ERANGE;
  
  	INIT_LIST_HEAD(&tasks);
  
  	rcu_read_lock();
  	sma = sem_obtain_object_check(ns, semid);
  	if (IS_ERR(sma)) {
  		rcu_read_unlock();
  		return PTR_ERR(sma);
  	}
  
  	if (semnum < 0 || semnum >= sma->sem_nsems) {
  		rcu_read_unlock();
  		return -EINVAL;
  	}
  
  
  	if (ipcperms(ns, &sma->sem_perm, S_IWUGO)) {
  		rcu_read_unlock();
  		return -EACCES;
  	}
  
  	err = security_sem_semctl(sma, SETVAL);
  	if (err) {
  		rcu_read_unlock();
  		return -EACCES;
  	}
  
  	sem_lock(sma, NULL, -1);
  
  	if (!ipc_valid_object(&sma->sem_perm)) {
  		sem_unlock(sma, -1);
  		rcu_read_unlock();
  		return -EIDRM;
  	}
  
  	curr = &sma->sem_base[semnum];
  
  	ipc_assert_locked_object(&sma->sem_perm);
  	list_for_each_entry(un, &sma->list_id, list_id)
  		un->semadj[semnum] = 0;
  
  	curr->semval = val;
  	curr->sempid = task_tgid_vnr(current);
  	sma->sem_ctime = get_seconds();
  	/* maybe some queued-up processes were waiting for this */
  	do_smart_update(sma, NULL, 0, 0, &tasks);
  	sem_unlock(sma, -1);
  	rcu_read_unlock();
  	wake_up_sem_queue_do(&tasks);
  	return 0;
  }
  
  static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
  		int cmd, void __user *p)
  {
  	struct sem_array *sma;
  	struct sem *curr;
  	int err, nsems;
  	ushort fast_sem_io[SEMMSL_FAST];
  	ushort *sem_io = fast_sem_io;
  	struct list_head tasks;
  
  	INIT_LIST_HEAD(&tasks);
  
  	rcu_read_lock();
  	sma = sem_obtain_object_check(ns, semid);
  	if (IS_ERR(sma)) {
  		rcu_read_unlock();
  		return PTR_ERR(sma);
  	}
  
  	nsems = sma->sem_nsems;
  
  	err = -EACCES;
  	if (ipcperms(ns, &sma->sem_perm, cmd == SETALL ? S_IWUGO : S_IRUGO))
  		goto out_rcu_wakeup;
  
  	err = security_sem_semctl(sma, cmd);
  	if (err)
  		goto out_rcu_wakeup;
  
  	err = -EACCES;
  	switch (cmd) {
  	case GETALL:
  	{
  		ushort __user *array = p;
  		int i;
  
  		sem_lock(sma, NULL, -1);
  		if (!ipc_valid_object(&sma->sem_perm)) {
  			err = -EIDRM;
  			goto out_unlock;
  		}
  		if (nsems > SEMMSL_FAST) {
  			if (!ipc_rcu_getref(sma)) {
  				err = -EIDRM;
  				goto out_unlock;
  			}
  			sem_unlock(sma, -1);
  			rcu_read_unlock();
  			sem_io = ipc_alloc(sizeof(ushort)*nsems);
  			if (sem_io == NULL) {
  				ipc_rcu_putref(sma, ipc_rcu_free);
  				return -ENOMEM;
  			}
  
  			rcu_read_lock();
  			sem_lock_and_putref(sma);
  			if (!ipc_valid_object(&sma->sem_perm)) {
  				err = -EIDRM;
  				goto out_unlock;
  			}
  		}
  		for (i = 0; i < sma->sem_nsems; i++)
  			sem_io[i] = sma->sem_base[i].semval;
  		sem_unlock(sma, -1);
  		rcu_read_unlock();
  		err = 0;
  		if (copy_to_user(array, sem_io, nsems*sizeof(ushort)))
  			err = -EFAULT;
  		goto out_free;
  	}
  	case SETALL:
  	{
  		int i;
  		struct sem_undo *un;
  
  		if (!ipc_rcu_getref(sma)) {
  			err = -EIDRM;
  			goto out_rcu_wakeup;
  		}
  		rcu_read_unlock();
  
  		if (nsems > SEMMSL_FAST) {
  			sem_io = ipc_alloc(sizeof(ushort)*nsems);
  			if (sem_io == NULL) {
  				ipc_rcu_putref(sma, ipc_rcu_free);
  				return -ENOMEM;
  			}
  		}
  
  		if (copy_from_user(sem_io, p, nsems*sizeof(ushort))) {
  			ipc_rcu_putref(sma, ipc_rcu_free);
  			err = -EFAULT;
  			goto out_free;
  		}
  
  		for (i = 0; i < nsems; i++) {
  			if (sem_io[i] > SEMVMX) {
  				ipc_rcu_putref(sma, ipc_rcu_free);
  				err = -ERANGE;
  				goto out_free;
  			}
  		}
  		rcu_read_lock();
  		sem_lock_and_putref(sma);
  		if (!ipc_valid_object(&sma->sem_perm)) {
  			err = -EIDRM;
  			goto out_unlock;
  		}
  
  		for (i = 0; i < nsems; i++)
  			sma->sem_base[i].semval = sem_io[i];
  
  		ipc_assert_locked_object(&sma->sem_perm);
  		list_for_each_entry(un, &sma->list_id, list_id) {
  			for (i = 0; i < nsems; i++)
  				un->semadj[i] = 0;
  		}
  		sma->sem_ctime = get_seconds();
  		/* maybe some queued-up processes were waiting for this */
  		do_smart_update(sma, NULL, 0, 0, &tasks);
  		err = 0;
  		goto out_unlock;
  	}
  	/* GETVAL, GETPID, GETNCTN, GETZCNT: fall-through */
  	}
  	err = -EINVAL;
  	if (semnum < 0 || semnum >= nsems)
  		goto out_rcu_wakeup;
  
  	sem_lock(sma, NULL, -1);
  	if (!ipc_valid_object(&sma->sem_perm)) {
  		err = -EIDRM;
  		goto out_unlock;
  	}
  	curr = &sma->sem_base[semnum];
  
  	switch (cmd) {
  	case GETVAL:
  		err = curr->semval;
  		goto out_unlock;
  	case GETPID:
  		err = curr->sempid;
  		goto out_unlock;
  	case GETNCNT:
  		err = count_semcnt(sma, semnum, 0);
  		goto out_unlock;
  	case GETZCNT:
  		err = count_semcnt(sma, semnum, 1);
  		goto out_unlock;
  	}
  
  out_unlock:
  	sem_unlock(sma, -1);
  out_rcu_wakeup:
  	rcu_read_unlock();
  	wake_up_sem_queue_do(&tasks);
  out_free:
  	if (sem_io != fast_sem_io)
  		ipc_free(sem_io);
  	return err;
  }
  
  static inline unsigned long
  copy_semid_from_user(struct semid64_ds *out, void __user *buf, int version)
  {
  	switch (version) {
  	case IPC_64:
  		if (copy_from_user(out, buf, sizeof(*out)))
  			return -EFAULT;
  		return 0;
  	case IPC_OLD:
  	    {
  		struct semid_ds tbuf_old;
  
  		if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
  			return -EFAULT;
  
  		out->sem_perm.uid	= tbuf_old.sem_perm.uid;
  		out->sem_perm.gid	= tbuf_old.sem_perm.gid;
  		out->sem_perm.mode	= tbuf_old.sem_perm.mode;
  
  		return 0;
  	    }
  	default:
  		return -EINVAL;
  	}
  }
  
  /*
   * This function handles some semctl commands which require the rwsem
   * to be held in write mode.
   * NOTE: no locks must be held, the rwsem is taken inside this function.
   */
  static int semctl_down(struct ipc_namespace *ns, int semid,
  		       int cmd, int version, void __user *p)
  {
  	struct sem_array *sma;
  	int err;
  	struct semid64_ds semid64;
  	struct kern_ipc_perm *ipcp;
  
  	if (cmd == IPC_SET) {
  		if (copy_semid_from_user(&semid64, p, version))
  			return -EFAULT;
  	}
  
  	down_write(&sem_ids(ns).rwsem);
  	rcu_read_lock();
  
  	ipcp = ipcctl_pre_down_nolock(ns, &sem_ids(ns), semid, cmd,
  				      &semid64.sem_perm, 0);
  	if (IS_ERR(ipcp)) {
  		err = PTR_ERR(ipcp);
  		goto out_unlock1;
  	}
  
  	sma = container_of(ipcp, struct sem_array, sem_perm);
  
  	err = security_sem_semctl(sma, cmd);
  	if (err)
  		goto out_unlock1;
  
  	switch (cmd) {
  	case IPC_RMID:
  		sem_lock(sma, NULL, -1);
  		/* freeary unlocks the ipc object and rcu */
  		freeary(ns, ipcp);
  		goto out_up;
  	case IPC_SET:
  		sem_lock(sma, NULL, -1);
  		err = ipc_update_perm(&semid64.sem_perm, ipcp);
  		if (err)
  			goto out_unlock0;
  		sma->sem_ctime = get_seconds();
  		break;
  	default:
  		err = -EINVAL;
  		goto out_unlock1;
  	}
  
  out_unlock0:
  	sem_unlock(sma, -1);
  out_unlock1:
  	rcu_read_unlock();
  out_up:
  	up_write(&sem_ids(ns).rwsem);
  	return err;
  }
  
  SYSCALL_DEFINE4(semctl, int, semid, int, semnum, int, cmd, unsigned long, arg)
  {
  	int version;
  	struct ipc_namespace *ns;
  	void __user *p = (void __user *)arg;
  
  	if (semid < 0)
  		return -EINVAL;
  
  	version = ipc_parse_version(&cmd);
  	ns = current->nsproxy->ipc_ns;
  
  	switch (cmd) {
  	case IPC_INFO:
  	case SEM_INFO:
  	case IPC_STAT:
  	case SEM_STAT:
  		return semctl_nolock(ns, semid, cmd, version, p);
  	case GETALL:
  	case GETVAL:
  	case GETPID:
  	case GETNCNT:
  	case GETZCNT:
  	case SETALL:
  		return semctl_main(ns, semid, semnum, cmd, p);
  	case SETVAL:
  		return semctl_setval(ns, semid, semnum, arg);
  	case IPC_RMID:
  	case IPC_SET:
  		return semctl_down(ns, semid, cmd, version, p);
  	default:
  		return -EINVAL;
  	}
  }
  
  /* If the task doesn't already have a undo_list, then allocate one
   * here.  We guarantee there is only one thread using this undo list,
   * and current is THE ONE
   *
   * If this allocation and assignment succeeds, but later
   * portions of this code fail, there is no need to free the sem_undo_list.
   * Just let it stay associated with the task, and it'll be freed later
   * at exit time.
   *
   * This can block, so callers must hold no locks.
   */
  static inline int get_undo_list(struct sem_undo_list **undo_listp)
  {
  	struct sem_undo_list *undo_list;
  
  	undo_list = current->sysvsem.undo_list;
  	if (!undo_list) {
  		undo_list = kzalloc(sizeof(*undo_list), GFP_KERNEL);
  		if (undo_list == NULL)
  			return -ENOMEM;
  		spin_lock_init(&undo_list->lock);
  		atomic_set(&undo_list->refcnt, 1);
  		INIT_LIST_HEAD(&undo_list->list_proc);
  
  		current->sysvsem.undo_list = undo_list;
  	}
  	*undo_listp = undo_list;
  	return 0;
  }
  
  static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid)
  {
  	struct sem_undo *un;
  
  	list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) {
  		if (un->semid == semid)
  			return un;
  	}
  	return NULL;
  }
  
  static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
  {
  	struct sem_undo *un;
  
  	assert_spin_locked(&ulp->lock);
  
  	un = __lookup_undo(ulp, semid);
  	if (un) {
  		list_del_rcu(&un->list_proc);
  		list_add_rcu(&un->list_proc, &ulp->list_proc);
  	}
  	return un;
  }
  
  /**
   * find_alloc_undo - lookup (and if not present create) undo array
   * @ns: namespace
   * @semid: semaphore array id
   *
   * The function looks up (and if not present creates) the undo structure.
   * The size of the undo structure depends on the size of the semaphore
   * array, thus the alloc path is not that straightforward.
   * Lifetime-rules: sem_undo is rcu-protected, on success, the function
   * performs a rcu_read_lock().
   */
  static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
  {
  	struct sem_array *sma;
  	struct sem_undo_list *ulp;
  	struct sem_undo *un, *new;
  	int nsems, error;
  
  	error = get_undo_list(&ulp);
  	if (error)
  		return ERR_PTR(error);
  
  	rcu_read_lock();
  	spin_lock(&ulp->lock);
  	un = lookup_undo(ulp, semid);
  	spin_unlock(&ulp->lock);
  	if (likely(un != NULL))
  		goto out;
  
  	/* no undo structure around - allocate one. */
  	/* step 1: figure out the size of the semaphore array */
  	sma = sem_obtain_object_check(ns, semid);
  	if (IS_ERR(sma)) {
  		rcu_read_unlock();
  		return ERR_CAST(sma);
  	}
  
  	nsems = sma->sem_nsems;
  	if (!ipc_rcu_getref(sma)) {
  		rcu_read_unlock();
  		un = ERR_PTR(-EIDRM);
  		goto out;
  	}
  	rcu_read_unlock();
  
  	/* step 2: allocate new undo structure */
  	new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
  	if (!new) {
  		ipc_rcu_putref(sma, ipc_rcu_free);
  		return ERR_PTR(-ENOMEM);
  	}
  
  	/* step 3: Acquire the lock on semaphore array */
  	rcu_read_lock();
  	sem_lock_and_putref(sma);
  	if (!ipc_valid_object(&sma->sem_perm)) {
  		sem_unlock(sma, -1);
  		rcu_read_unlock();
  		kfree(new);
  		un = ERR_PTR(-EIDRM);
  		goto out;
  	}
  	spin_lock(&ulp->lock);
  
  	/*
  	 * step 4: check for races: did someone else allocate the undo struct?
  	 */
  	un = lookup_undo(ulp, semid);
  	if (un) {
  		kfree(new);
  		goto success;
  	}
  	/* step 5: initialize & link new undo structure */
  	new->semadj = (short *) &new[1];
  	new->ulp = ulp;
  	new->semid = semid;
  	assert_spin_locked(&ulp->lock);
  	list_add_rcu(&new->list_proc, &ulp->list_proc);
  	ipc_assert_locked_object(&sma->sem_perm);
  	list_add(&new->list_id, &sma->list_id);
  	un = new;
  
  success:
  	spin_unlock(&ulp->lock);
  	sem_unlock(sma, -1);
  out:
  	return un;
  }
  
  
  /**
   * get_queue_result - retrieve the result code from sem_queue
   * @q: Pointer to queue structure
   *
   * Retrieve the return code from the pending queue. If IN_WAKEUP is found in
   * q->status, then we must loop until the value is replaced with the final
   * value: This may happen if a task is woken up by an unrelated event (e.g.
   * signal) and in parallel the task is woken up by another task because it got
   * the requested semaphores.
   *
   * The function can be called with or without holding the semaphore spinlock.
   */
  static int get_queue_result(struct sem_queue *q)
  {
  	int error;
  
  	error = q->status;
  	while (unlikely(error == IN_WAKEUP)) {
  		cpu_relax();
  		error = q->status;
  	}
  
  	return error;
  }
  
  SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
  		unsigned, nsops, const struct timespec __user *, timeout)
  {
  	int error = -EINVAL;
  	struct sem_array *sma;
  	struct sembuf fast_sops[SEMOPM_FAST];
  	struct sembuf *sops = fast_sops, *sop;
  	struct sem_undo *un;
  	int undos = 0, alter = 0, max, locknum;
  	struct sem_queue queue;
  	unsigned long jiffies_left = 0;
  	struct ipc_namespace *ns;
  	struct list_head tasks;
  
  	ns = current->nsproxy->ipc_ns;
  
  	if (nsops < 1 || semid < 0)
  		return -EINVAL;
  	if (nsops > ns->sc_semopm)
  		return -E2BIG;
  	if (nsops > SEMOPM_FAST) {
  		sops = kmalloc(sizeof(*sops)*nsops, GFP_KERNEL);
  		if (sops == NULL)
  			return -ENOMEM;
  	}
  	if (copy_from_user(sops, tsops, nsops * sizeof(*tsops))) {
  		error =  -EFAULT;
  		goto out_free;
  	}
  	if (timeout) {
  		struct timespec _timeout;
  		if (copy_from_user(&_timeout, timeout, sizeof(*timeout))) {
  			error = -EFAULT;
  			goto out_free;
  		}
  		if (_timeout.tv_sec < 0 || _timeout.tv_nsec < 0 ||
  			_timeout.tv_nsec >= 1000000000L) {
  			error = -EINVAL;
  			goto out_free;
  		}
  		jiffies_left = timespec_to_jiffies(&_timeout);
  	}
  	max = 0;
  	for (sop = sops; sop < sops + nsops; sop++) {
  		if (sop->sem_num >= max)
  			max = sop->sem_num;
  		if (sop->sem_flg & SEM_UNDO)
  			undos = 1;
  		if (sop->sem_op != 0)
  			alter = 1;
  	}
  
  	INIT_LIST_HEAD(&tasks);
  
  	if (undos) {
  		/* On success, find_alloc_undo takes the rcu_read_lock */
  		un = find_alloc_undo(ns, semid);
  		if (IS_ERR(un)) {
  			error = PTR_ERR(un);
  			goto out_free;
  		}
  	} else {
  		un = NULL;
  		rcu_read_lock();
  	}
  
  	sma = sem_obtain_object_check(ns, semid);
  	if (IS_ERR(sma)) {
  		rcu_read_unlock();
  		error = PTR_ERR(sma);
  		goto out_free;
  	}
  
  	error = -EFBIG;
  	if (max >= sma->sem_nsems)
  		goto out_rcu_wakeup;
  
  	error = -EACCES;
  	if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
  		goto out_rcu_wakeup;
  
  	error = security_sem_semop(sma, sops, nsops, alter);
  	if (error)
  		goto out_rcu_wakeup;
  
  	error = -EIDRM;
  	locknum = sem_lock(sma, sops, nsops);
  	/*
  	 * We eventually might perform the following check in a lockless
  	 * fashion, considering ipc_valid_object() locking constraints.
  	 * If nsops == 1 and there is no contention for sem_perm.lock, then
  	 * only a per-semaphore lock is held and it's OK to proceed with the
  	 * check below. More details on the fine grained locking scheme
  	 * entangled here and why it's RMID race safe on comments at sem_lock()
  	 */
  	if (!ipc_valid_object(&sma->sem_perm))
  		goto out_unlock_free;
  	/*
  	 * semid identifiers are not unique - find_alloc_undo may have
  	 * allocated an undo structure, it was invalidated by an RMID
  	 * and now a new array with received the same id. Check and fail.
  	 * This case can be detected checking un->semid. The existence of
  	 * "un" itself is guaranteed by rcu.
  	 */
  	if (un && un->semid == -1)
  		goto out_unlock_free;
  
  	queue.sops = sops;
  	queue.nsops = nsops;
  	queue.undo = un;
  	queue.pid = task_tgid_vnr(current);
  	queue.alter = alter;
  
  	error = perform_atomic_semop(sma, &queue);
  	if (error == 0) {
  		/* If the operation was successful, then do
  		 * the required updates.
  		 */
  		if (alter)
  			do_smart_update(sma, sops, nsops, 1, &tasks);
  		else
  			set_semotime(sma, sops);
  	}
  	if (error <= 0)
  		goto out_unlock_free;
  
  	/* We need to sleep on this operation, so we put the current
  	 * task into the pending queue and go to sleep.
  	 */
  
  	if (nsops == 1) {
  		struct sem *curr;
  		curr = &sma->sem_base[sops->sem_num];
  
  		if (alter) {
  			if (sma->complex_count) {
  				list_add_tail(&queue.list,
  						&sma->pending_alter);
  			} else {
  
  				list_add_tail(&queue.list,
  						&curr->pending_alter);
  			}
  		} else {
  			list_add_tail(&queue.list, &curr->pending_const);
  		}
  	} else {
  		if (!sma->complex_count)
  			merge_queues(sma);
  
  		if (alter)
  			list_add_tail(&queue.list, &sma->pending_alter);
  		else
  			list_add_tail(&queue.list, &sma->pending_const);
  
  		sma->complex_count++;
  	}
  
  	queue.status = -EINTR;
  	queue.sleeper = current;
  
  sleep_again:
  	__set_current_state(TASK_INTERRUPTIBLE);
  	sem_unlock(sma, locknum);
  	rcu_read_unlock();
  
  	if (timeout)
  		jiffies_left = schedule_timeout(jiffies_left);
  	else
  		schedule();
  
  	error = get_queue_result(&queue);
  
  	if (error != -EINTR) {
  		/* fast path: update_queue already obtained all requested
  		 * resources.
  		 * Perform a smp_mb(): User space could assume that semop()
  		 * is a memory barrier: Without the mb(), the cpu could
  		 * speculatively read in user space stale data that was
  		 * overwritten by the previous owner of the semaphore.
  		 */
  		smp_mb();
  
  		goto out_free;
  	}
  
  	rcu_read_lock();
  	sma = sem_obtain_lock(ns, semid, sops, nsops, &locknum);
  
  	/*
  	 * Wait until it's guaranteed that no wakeup_sem_queue_do() is ongoing.
  	 */
  	error = get_queue_result(&queue);
  
  	/*
  	 * Array removed? If yes, leave without sem_unlock().
  	 */
  	if (IS_ERR(sma)) {
  		rcu_read_unlock();
  		goto out_free;
  	}
  
  
  	/*
  	 * If queue.status != -EINTR we are woken up by another process.
  	 * Leave without unlink_queue(), but with sem_unlock().
  	 */
  	if (error != -EINTR)
  		goto out_unlock_free;
  
  	/*
  	 * If an interrupt occurred we have to clean up the queue
  	 */
  	if (timeout && jiffies_left == 0)
  		error = -EAGAIN;
  
  	/*
  	 * If the wakeup was spurious, just retry
  	 */
  	if (error == -EINTR && !signal_pending(current))
  		goto sleep_again;
  
  	unlink_queue(sma, &queue);
  
  out_unlock_free:
  	sem_unlock(sma, locknum);
  out_rcu_wakeup:
  	rcu_read_unlock();
  	wake_up_sem_queue_do(&tasks);
  out_free:
  	if (sops != fast_sops)
  		kfree(sops);
  	return error;
  }
  
  SYSCALL_DEFINE3(semop, int, semid, struct sembuf __user *, tsops,
  		unsigned, nsops)
  {
  	return sys_semtimedop(semid, tsops, nsops, NULL);
  }
  
  /* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between
   * parent and child tasks.
   */
  
  int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
  {
  	struct sem_undo_list *undo_list;
  	int error;
  
  	if (clone_flags & CLONE_SYSVSEM) {
  		error = get_undo_list(&undo_list);
  		if (error)
  			return error;
  		atomic_inc(&undo_list->refcnt);
  		tsk->sysvsem.undo_list = undo_list;
  	} else
  		tsk->sysvsem.undo_list = NULL;
  
  	return 0;
  }
  
  /*
   * add semadj values to semaphores, free undo structures.
   * undo structures are not freed when semaphore arrays are destroyed
   * so some of them may be out of date.
   * IMPLEMENTATION NOTE: There is some confusion over whether the
   * set of adjustments that needs to be done should be done in an atomic
   * manner or not. That is, if we are attempting to decrement the semval
   * should we queue up and wait until we can do so legally?
   * The original implementation attempted to do this (queue and wait).
   * The current implementation does not do so. The POSIX standard
   * and SVID should be consulted to determine what behavior is mandated.
   */
  void exit_sem(struct task_struct *tsk)
  {
  	struct sem_undo_list *ulp;
  
  	ulp = tsk->sysvsem.undo_list;
  	if (!ulp)
  		return;
  	tsk->sysvsem.undo_list = NULL;
  
  	if (!atomic_dec_and_test(&ulp->refcnt))
  		return;
  
  	for (;;) {
  		struct sem_array *sma;
  		struct sem_undo *un;
  		struct list_head tasks;
  		int semid, i;
  
  		rcu_read_lock();
  		un = list_entry_rcu(ulp->list_proc.next,
  				    struct sem_undo, list_proc);
  		if (&un->list_proc == &ulp->list_proc) {
  			/*
  			 * We must wait for freeary() before freeing this ulp,
  			 * in case we raced with last sem_undo. There is a small
  			 * possibility where we exit while freeary() didn't
  			 * finish unlocking sem_undo_list.
  			 */
  			spin_unlock_wait(&ulp->lock);
  			rcu_read_unlock();
  			break;
  		}
  		spin_lock(&ulp->lock);
  		semid = un->semid;
  		spin_unlock(&ulp->lock);
  
  		/* exit_sem raced with IPC_RMID, nothing to do */
  		if (semid == -1) {
  			rcu_read_unlock();
  			continue;
  		}
  
  		sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, semid);
  		/* exit_sem raced with IPC_RMID, nothing to do */
  		if (IS_ERR(sma)) {
  			rcu_read_unlock();
  			continue;
  		}
  
  		sem_lock(sma, NULL, -1);
  		/* exit_sem raced with IPC_RMID, nothing to do */
  		if (!ipc_valid_object(&sma->sem_perm)) {
  			sem_unlock(sma, -1);
  			rcu_read_unlock();
  			continue;
  		}
  		un = __lookup_undo(ulp, semid);
  		if (un == NULL) {
  			/* exit_sem raced with IPC_RMID+semget() that created
  			 * exactly the same semid. Nothing to do.
  			 */
  			sem_unlock(sma, -1);
  			rcu_read_unlock();
  			continue;
  		}
  
  		/* remove un from the linked lists */
  		ipc_assert_locked_object(&sma->sem_perm);
  		list_del(&un->list_id);
  
  		/* we are the last process using this ulp, acquiring ulp->lock
  		 * isn't required. Besides that, we are also protected against
  		 * IPC_RMID as we hold sma->sem_perm lock now
  		 */
  		list_del_rcu(&un->list_proc);
  
  		/* perform adjustments registered in un */
  		for (i = 0; i < sma->sem_nsems; i++) {
  			struct sem *semaphore = &sma->sem_base[i];
  			if (un->semadj[i]) {
  				semaphore->semval += un->semadj[i];
  				/*
  				 * Range checks of the new semaphore value,
  				 * not defined by sus:
  				 * - Some unices ignore the undo entirely
  				 *   (e.g. HP UX 11i 11.22, Tru64 V5.1)
  				 * - some cap the value (e.g. FreeBSD caps
  				 *   at 0, but doesn't enforce SEMVMX)
  				 *
  				 * Linux caps the semaphore value, both at 0
  				 * and at SEMVMX.
  				 *
  				 *	Manfred <manfred@colorfullife.com>
  				 */
  				if (semaphore->semval < 0)
  					semaphore->semval = 0;
  				if (semaphore->semval > SEMVMX)
  					semaphore->semval = SEMVMX;
  				semaphore->sempid = task_tgid_vnr(current);
  			}
  		}
  		/* maybe some queued-up processes were waiting for this */
  		INIT_LIST_HEAD(&tasks);
  		do_smart_update(sma, NULL, 0, 1, &tasks);
  		sem_unlock(sma, -1);
  		rcu_read_unlock();
  		wake_up_sem_queue_do(&tasks);
  
  		kfree_rcu(un, rcu);
  	}
  	kfree(ulp);
  }
  
  #ifdef CONFIG_PROC_FS
  static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
  {
  	struct user_namespace *user_ns = seq_user_ns(s);
  	struct sem_array *sma = it;
  	time_t sem_otime;
  
  	/*
  	 * The proc interface isn't aware of sem_lock(), it calls
  	 * ipc_lock_object() directly (in sysvipc_find_ipc).
  	 * In order to stay compatible with sem_lock(), we must wait until
  	 * all simple semop() calls have left their critical regions.
  	 */
  	sem_wait_array(sma);
  
  	sem_otime = get_semotime(sma);
  
  	seq_printf(s,
  		   "%10d %10d  %4o %10u %5u %5u %5u %5u %10lu %10lu\n",
  		   sma->sem_perm.key,
  		   sma->sem_perm.id,
  		   sma->sem_perm.mode,
  		   sma->sem_nsems,
  		   from_kuid_munged(user_ns, sma->sem_perm.uid),
  		   from_kgid_munged(user_ns, sma->sem_perm.gid),
  		   from_kuid_munged(user_ns, sma->sem_perm.cuid),
  		   from_kgid_munged(user_ns, sma->sem_perm.cgid),
  		   sem_otime,
  		   sma->sem_ctime);
  
  	return 0;
  }
  #endif
  