Initial import

1 files changed, 2188 insertions, 0 deletions

diff --git a/ipc/sem.c b/ipc/sem.c
new file mode 100644
index 000000000..d1a6edd17
--- /dev/null
+++ b/ipc/sem.c
@@ -0,0 +1,2188 @@
+/*
+ * 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);
+}
+
+/*
+ * 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);
+	}
+}
+
+/*
+ * 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)) {
+			/*
+			 * The ipc object lock check must be visible on all
+			 * cores before rechecking the complex count.  Otherwise
+			 * we can race with  another thread that does:
+			 *	complex_count++;
+			 *	spin_unlock(sem_perm.lock);
+			 */
+			smp_rmb();
+
+			/*
+			 * 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(&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(&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, sizeof(ushort)*nsems);
+	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)
+			semid = -1;
+		 else
+			semid = un->semid;
+
+		if (semid == -1) {
+			rcu_read_unlock();
+			break;
+		}
+
+		sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, un->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);
+
+		spin_lock(&ulp->lock);
+		list_del_rcu(&un->list_proc);
+		spin_unlock(&ulp->lock);
+
+		/* 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