sem.c

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/*
 * linux/ipc/sem.c
 * Copyright (C) 1992 Krishna Balasubramanian
 * Copyright (C) 1995 Eric Schenk, Bruno Haible
 *
 * /proc/sysvipc/sem support (c) 1999 Dragos Acostachioaie <[email protected]>
 *
 * SMP-threaded, sysctl's added
 * (c) 1999 Manfred Spraul <[email protected]>
 * Enforced range limit on SEM_UNDO
 * (c) 2001 Red Hat Inc
 * Lockless wakeup
 * (c) 2003 Manfred Spraul <[email protected]>
 * Further wakeup optimizations, documentation
 * (c) 2010 Manfred Spraul <[email protected]>
 *
 * support for audit of ipc object properties and permission changes
 * Dustin Kirkland <[email protected]>
 *
 * namespaces support
 * OpenVZ, SWsoft Inc.
 * Pavel Emelianov <[email protected]>
 *
 * 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_semncnt() and
 *   count_semzcnt()
 * - 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 <asm/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 */
    struct list_head sem_pending; /* pending single-sop operations */
};

/* One queue for each sleeping process in the system. */
struct sem_queue {
    struct list_head    simple_list; /* queue of pending operations */
    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 */
    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_unlock(sma)     ipc_unlock(&(sma)->sem_perm)
#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 */

/*
 * linked list protection:
 *  sem_undo.id_next,
 *  sem_array.sem_pending{,last},
 *  sem_array.sem_undo: sem_lock() for read/write
 *  sem_undo.proc_next: only "current" is allowed to read/write that field.
 *  
 */

#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);
}

/*
 * sem_lock_(check_) routines are called in the paths where the rw_mutex
 * is not held.
 */
static inline struct sem_array *sem_lock(struct ipc_namespace *ns, int id)
{
    struct kern_ipc_perm *ipcp = ipc_lock(&sem_ids(ns), id);

    if (IS_ERR(ipcp))
        return (struct sem_array *)ipcp;

    return container_of(ipcp, struct sem_array, sem_perm);
}

static inline struct sem_array *sem_lock_check(struct ipc_namespace *ns,
                        int id)
{
    struct kern_ipc_perm *ipcp = ipc_lock_check(&sem_ids(ns), id);

    if (IS_ERR(ipcp))
        return (struct sem_array *)ipcp;

    return container_of(ipcp, struct sem_array, sem_perm);
}

static inline void sem_lock_and_putref(struct sem_array *sma)
{
    ipc_lock_by_ptr(&sma->sem_perm);
    ipc_rcu_putref(sma);
}

static inline void sem_getref_and_unlock(struct sem_array *sma)
{
    ipc_rcu_getref(sma);
    ipc_unlock(&(sma)->sem_perm);
}

static inline void sem_putref(struct sem_array *sma)
{
    ipc_lock_by_ptr(&sma->sem_perm);
    ipc_rcu_putref(sma);
    ipc_unlock(&(sma)->sem_perm);
}

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 sma->sem_pending
 *  * 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

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);
        return retval;
    }

    id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
    if (id < 0) {
        security_sem_free(sma);
        ipc_rcu_putref(sma);
        return id;
    }
    ns->used_sems += nsems;

    sma->sem_base = (struct sem *) &sma[1];

    for (i = 0; i < nsems; i++)
        INIT_LIST_HEAD(&sma->sem_base[i].sem_pending);

    sma->complex_count = 0;
    INIT_LIST_HEAD(&sma->sem_pending);
    INIT_LIST_HEAD(&sma->list_id);
    sma->sem_nsems = nsems;
    sma->sem_ctime = get_seconds();
    sem_unlock(sma);

    return sma->sem_perm.id;
}


/*
 * Called with sem_ids.rw_mutex 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.rw_mutex 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;
    struct ipc_ops sem_ops;
    struct ipc_params sem_params;

    ns = current->nsproxy->ipc_ns;

    if (nsems < 0 || nsems > ns->sc_semmsl)
        return -EINVAL;

    sem_ops.getnew = newary;
    sem_ops.associate = sem_security;
    sem_ops.more_checks = sem_more_checks;

    sem_params.key = key;
    sem_params.flg = semflg;
    sem_params.u.nsems = nsems;

    return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
}

/*
 * Determine whether a sequence of semaphore operations would succeed
 * all at once. Return 0 if yes, 1 if need to sleep, else return error code.
 */

static int try_atomic_semop (struct sem_array * sma, struct sembuf * sops,
                 int nsops, struct sem_undo *un, int pid)
{
    int result, sem_op;
    struct sembuf *sop;
    struct sem * curr;

    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;
        }
        curr->semval = result;
    }

    sop--;
    while (sop >= sops) {
        sma->sem_base[sop->sem_num].sempid = pid;
        if (sop->sem_flg & SEM_UNDO)
            un->semadj[sop->sem_num] -= sop->sem_op;
        sop--;
    }
    
    return 0;

out_of_range:
    result = -ERANGE;
    goto undo;

would_block:
    if (sop->sem_flg & IPC_NOWAIT)
        result = -EAGAIN;
    else
        result = 1;

undo:
    sop--;
    while (sop >= sops) {
        sma->sem_base[sop->sem_num].semval -= sop->sem_op;
        sop--;
    }

    return result;
}

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->simple_list, pt);
}

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, simple_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)
        list_del(&q->simple_list);
    else
        sma->complex_count--;
}

static int check_restart(struct sem_array *sma, struct sem_queue *q)
{
    struct sem *curr;
    struct sem_queue *h;

    /* if the operation didn't modify the array, then no restart */
    if (q->alter == 0)
        return 0;

    /* pending complex operations are too difficult to analyse */
    if (sma->complex_count)
        return 1;

    /* we were a sleeping complex operation. Too difficult */
    if (q->nsops > 1)
        return 1;

    curr = sma->sem_base + q->sops[0].sem_num;

    /* No-one waits on this queue */
    if (list_empty(&curr->sem_pending))
        return 0;

    /* the new semaphore value */
    if (curr->semval) {
        /* It is impossible that someone waits for the new value:
         * - q is a previously sleeping simple operation that
         *   altered the array. It must be a decrement, because
         *   simple increments never sleep.
         * - The value is not 0, thus wait-for-zero won't proceed.
         * - 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.
         */
        BUG_ON(q->sops[0].sem_op >= 0);
        return 0;
    }
    /*
     * semval is 0. Check if there are wait-for-zero semops.
     * They must be the first entries in the per-semaphore simple queue
     */
    h = list_first_entry(&curr->sem_pending, struct sem_queue, simple_list);
    BUG_ON(h->nsops != 1);
    BUG_ON(h->sops[0].sem_num != q->sops[0].sem_num);

    /* Yes, there is a wait-for-zero semop. Restart */
    if (h->sops[0].sem_op == 0)
        return 1;

    /* Again - no-one is waiting for the new value. */
    return 0;
}


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 offset;
    int semop_completed = 0;

    /* if there are complex operations around, then knowing the semaphore
     * that was modified doesn't help us. Assume that multiple semaphores
     * were modified.
     */
    if (sma->complex_count)
        semnum = -1;

    if (semnum == -1) {
        pending_list = &sma->sem_pending;
        offset = offsetof(struct sem_queue, list);
    } else {
        pending_list = &sma->sem_base[semnum].sem_pending;
        offset = offsetof(struct sem_queue, simple_list);
    }

again:
    walk = pending_list->next;
    while (walk != pending_list) {
        int error, restart;

        q = (struct sem_queue *)((char *)walk - offset);
        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 the "alter" entries: 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 &&
                q->alter)
            break;

        error = try_atomic_semop(sma, q->sops, q->nsops,
                     q->undo, q->pid);

        /* Does q->sleeper still need to sleep? */
        if (error > 0)
            continue;

        unlink_queue(sma, q);

        if (error) {
            restart = 0;
        } else {
            semop_completed = 1;
            restart = check_restart(sma, q);
        }

        wake_up_sem_queue_prepare(pt, q, error);
        if (restart)
            goto again;
    }
    return semop_completed;
}

static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops,
            int otime, struct list_head *pt)
{
    int i;

    if (sma->complex_count || sops == NULL) {
        if (update_queue(sma, -1, pt))
            otime = 1;
        goto done;
    }

    for (i = 0; i < nsops; i++) {
        if (sops[i].sem_op > 0 ||
            (sops[i].sem_op < 0 &&
                sma->sem_base[sops[i].sem_num].semval == 0))
            if (update_queue(sma, sops[i].sem_num, pt))
                otime = 1;
    }
done:
    if (otime)
        sma->sem_otime = get_seconds();
}


/* 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
 * This model assumes that a task waits on exactly one semaphore.
 * Since semaphore operations are to be performed atomically, tasks actually
 * wait on a whole sequence of semaphores simultaneously.
 * The counts we return here are a rough approximation, but still
 * warrant that semncnt+semzcnt>0 if the task is on the pending queue.
 */
static int count_semncnt (struct sem_array * sma, ushort semnum)
{
    int semncnt;
    struct sem_queue * q;

    semncnt = 0;
    list_for_each_entry(q, &sma->sem_pending, list) {
        struct sembuf * sops = q->sops;
        int nsops = q->nsops;
        int i;
        for (i = 0; i < nsops; i++)
            if (sops[i].sem_num == semnum
                && (sops[i].sem_op < 0)
                && !(sops[i].sem_flg & IPC_NOWAIT))
                semncnt++;
    }
    return semncnt;
}

static int count_semzcnt (struct sem_array * sma, ushort semnum)
{
    int semzcnt;
    struct sem_queue * q;

    semzcnt = 0;
    list_for_each_entry(q, &sma->sem_pending, list) {
        struct sembuf * sops = q->sops;
        int nsops = q->nsops;
        int i;
        for (i = 0; i < nsops; i++)
            if (sops[i].sem_num == semnum
                && (sops[i].sem_op == 0)
                && !(sops[i].sem_flg & IPC_NOWAIT))
                semzcnt++;
    }
    return semzcnt;
}

/* Free a semaphore set. freeary() is called with sem_ids.rw_mutex locked
 * as a writer and the spinlock for this semaphore set hold. sem_ids.rw_mutex
 * 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;

    /* Free the existing undo structures for this semaphore set.  */
    assert_spin_locked(&sma->sem_perm.lock);
    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->sem_pending, 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);

    wake_up_sem_queue_do(&tasks);
    ns->used_sems -= sma->sem_nsems;
    security_sem_free(sma);
    ipc_rcu_putref(sma);
}

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 int semctl_nolock(struct ipc_namespace *ns, int semid,
             int cmd, int version, union semun arg)
{
    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).rw_mutex);
        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).rw_mutex);
        if (copy_to_user (arg.__buf, &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;

        if (cmd == SEM_STAT) {
            sma = sem_lock(ns, semid);
            if (IS_ERR(sma))
                return PTR_ERR(sma);
            id = sma->sem_perm.id;
        } else {
            sma = sem_lock_check(ns, semid);
            if (IS_ERR(sma))
                return PTR_ERR(sma);
            id = 0;
        }

        err = -EACCES;
        if (ipcperms(ns, &sma->sem_perm, S_IRUGO))
            goto out_unlock;

        err = security_sem_semctl(sma, cmd);
        if (err)
            goto out_unlock;

        memset(&tbuf, 0, sizeof(tbuf));

        kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
        tbuf.sem_otime  = sma->sem_otime;
        tbuf.sem_ctime  = sma->sem_ctime;
        tbuf.sem_nsems  = sma->sem_nsems;
        sem_unlock(sma);
        if (copy_semid_to_user (arg.buf, &tbuf, version))
            return -EFAULT;
        return id;
    }
    default:
        return -EINVAL;
    }
out_unlock:
    sem_unlock(sma);
    return err;
}

static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
        int cmd, int version, union semun arg)
{
    struct sem_array *sma;
    struct sem* curr;
    int err;
    ushort fast_sem_io[SEMMSL_FAST];
    ushort* sem_io = fast_sem_io;
    int nsems;
    struct list_head tasks;

    sma = sem_lock_check(ns, semid);
    if (IS_ERR(sma))
        return PTR_ERR(sma);

    INIT_LIST_HEAD(&tasks);
    nsems = sma->sem_nsems;

    err = -EACCES;
    if (ipcperms(ns, &sma->sem_perm,
            (cmd == SETVAL || cmd == SETALL) ? S_IWUGO : S_IRUGO))
        goto out_unlock;

    err = security_sem_semctl(sma, cmd);
    if (err)
        goto out_unlock;

    err = -EACCES;
    switch (cmd) {
    case GETALL:
    {
        ushort __user *array = arg.array;
        int i;

        if(nsems > SEMMSL_FAST) {
            sem_getref_and_unlock(sma);

            sem_io = ipc_alloc(sizeof(ushort)*nsems);
            if(sem_io == NULL) {
                sem_putref(sma);
                return -ENOMEM;
            }

            sem_lock_and_putref(sma);
            if (sma->sem_perm.deleted) {
                sem_unlock(sma);
                err = -EIDRM;
                goto out_free;
            }
        }

        for (i = 0; i < sma->sem_nsems; i++)
            sem_io[i] = sma->sem_base[i].semval;
        sem_unlock(sma);
        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;

        sem_getref_and_unlock(sma);

        if(nsems > SEMMSL_FAST) {
            sem_io = ipc_alloc(sizeof(ushort)*nsems);
            if(sem_io == NULL) {
                sem_putref(sma);
                return -ENOMEM;
            }
        }

        if (copy_from_user (sem_io, arg.array, nsems*sizeof(ushort))) {
            sem_putref(sma);
            err = -EFAULT;
            goto out_free;
        }

        for (i = 0; i < nsems; i++) {
            if (sem_io[i] > SEMVMX) {
                sem_putref(sma);
                err = -ERANGE;
                goto out_free;
            }
        }
        sem_lock_and_putref(sma);
        if (sma->sem_perm.deleted) {
            sem_unlock(sma);
            err = -EIDRM;
            goto out_free;
        }

        for (i = 0; i < nsems; i++)
            sma->sem_base[i].semval = sem_io[i];

        assert_spin_locked(&sma->sem_perm.lock);
        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, SETVAL: fall-through */
    }
    err = -EINVAL;
    if(semnum < 0 || semnum >= nsems)
        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_semncnt(sma,semnum);
        goto out_unlock;
    case GETZCNT:
        err = count_semzcnt(sma,semnum);
        goto out_unlock;
    case SETVAL:
    {
        int val = arg.val;
        struct sem_undo *un;

        err = -ERANGE;
        if (val > SEMVMX || val < 0)
            goto out_unlock;

        assert_spin_locked(&sma->sem_perm.lock);
        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);
        err = 0;
        goto out_unlock;
    }
    }
out_unlock:
    sem_unlock(sma);
    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 rw_mutex
 * to be held in write mode.
 * NOTE: no locks must be held, the rw_mutex is taken inside this function.
 */
static int semctl_down(struct ipc_namespace *ns, int semid,
               int cmd, int version, union semun arg)
{
    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, arg.buf, version))
            return -EFAULT;
    }

    ipcp = ipcctl_pre_down(ns, &sem_ids(ns), semid, cmd,
                   &semid64.sem_perm, 0);
    if (IS_ERR(ipcp))
        return PTR_ERR(ipcp);

    sma = container_of(ipcp, struct sem_array, sem_perm);

    err = security_sem_semctl(sma, cmd);
    if (err)
        goto out_unlock;

    switch(cmd){
    case IPC_RMID:
        freeary(ns, ipcp);
        goto out_up;
    case IPC_SET:
        err = ipc_update_perm(&semid64.sem_perm, ipcp);
        if (err)
            goto out_unlock;
        sma->sem_ctime = get_seconds();
        break;
    default:
        err = -EINVAL;
    }

out_unlock:
    sem_unlock(sma);
out_up:
    up_write(&sem_ids(ns).rw_mutex);
    return err;
}

SYSCALL_DEFINE(semctl)(int semid, int semnum, int cmd, union semun arg)
{
    int err = -EINVAL;
    int version;
    struct ipc_namespace *ns;

    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:
        err = semctl_nolock(ns, semid, cmd, version, arg);
        return err;
    case GETALL:
    case GETVAL:
    case GETPID:
    case GETNCNT:
    case GETZCNT:
    case SETVAL:
    case SETALL:
        err = semctl_main(ns,semid,semnum,cmd,version,arg);
        return err;
    case IPC_RMID:
    case IPC_SET:
        err = semctl_down(ns, semid, cmd, version, arg);
        return err;
    default:
        return -EINVAL;
    }
}
#ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
asmlinkage long SyS_semctl(int semid, int semnum, int cmd, union semun arg)
{
    return SYSC_semctl((int) semid, (int) semnum, (int) cmd, arg);
}
SYSCALL_ALIAS(sys_semctl, SyS_semctl);
#endif

/* 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;
}

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;
    int 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;
    rcu_read_unlock();

    /* no undo structure around - allocate one. */
    /* step 1: figure out the size of the semaphore array */
    sma = sem_lock_check(ns, semid);
    if (IS_ERR(sma))
        return ERR_CAST(sma);

    nsems = sma->sem_nsems;
    sem_getref_and_unlock(sma);

    /* step 2: allocate new undo structure */
    new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
    if (!new) {
        sem_putref(sma);
        return ERR_PTR(-ENOMEM);
    }

    /* step 3: Acquire the lock on semaphore array */
    sem_lock_and_putref(sma);
    if (sma->sem_perm.deleted) {
        sem_unlock(sma);
        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);
    assert_spin_locked(&sma->sem_perm.lock);
    list_add(&new->list_id, &sma->list_id);
    un = new;

success:
    spin_unlock(&ulp->lock);
    rcu_read_lock();
    sem_unlock(sma);
out:
    return un;
}


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;
    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;
    }

    if (undos) {
        un = find_alloc_undo(ns, semid);
        if (IS_ERR(un)) {
            error = PTR_ERR(un);
            goto out_free;
        }
    } else
        un = NULL;

    INIT_LIST_HEAD(&tasks);

    sma = sem_lock_check(ns, semid);
    if (IS_ERR(sma)) {
        if (un)
            rcu_read_unlock();
        error = PTR_ERR(sma);
        goto out_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.
     */
    error = -EIDRM;
    if (un) {
        if (un->semid == -1) {
            rcu_read_unlock();
            goto out_unlock_free;
        } else {
            /*
             * rcu lock can be released, "un" cannot disappear:
             * - sem_lock is acquired, thus IPC_RMID is
             *   impossible.
             * - exit_sem is impossible, it always operates on
             *   current (or a dead task).
             */

            rcu_read_unlock();
        }
    }

    error = -EFBIG;
    if (max >= sma->sem_nsems)
        goto out_unlock_free;

    error = -EACCES;
    if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
        goto out_unlock_free;

    error = security_sem_semop(sma, sops, nsops, alter);
    if (error)
        goto out_unlock_free;

    error = try_atomic_semop (sma, sops, nsops, un, task_tgid_vnr(current));
    if (error <= 0) {
        if (alter && error == 0)
            do_smart_update(sma, sops, nsops, 1, &tasks);

        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.
     */
        
    queue.sops = sops;
    queue.nsops = nsops;
    queue.undo = un;
    queue.pid = task_tgid_vnr(current);
    queue.alter = alter;
    if (alter)
        list_add_tail(&queue.list, &sma->sem_pending);
    else
        list_add(&queue.list, &sma->sem_pending);

    if (nsops == 1) {
        struct sem *curr;
        curr = &sma->sem_base[sops->sem_num];

        if (alter)
            list_add_tail(&queue.simple_list, &curr->sem_pending);
        else
            list_add(&queue.simple_list, &curr->sem_pending);
    } else {
        INIT_LIST_HEAD(&queue.simple_list);
        sma->complex_count++;
    }

    queue.status = -EINTR;
    queue.sleeper = current;

sleep_again:
    current->state = TASK_INTERRUPTIBLE;
    sem_unlock(sma);

    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;
    }

    sma = sem_lock(ns, semid);

    /*
     * 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)) {
        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);

    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;
        int 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;
        rcu_read_unlock();

        if (semid == -1)
            break;

        sma = sem_lock_check(tsk->nsproxy->ipc_ns, un->semid);

        /* exit_sem raced with IPC_RMID, nothing to do */
        if (IS_ERR(sma))
            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);
            continue;
        }

        /* remove un from the linked lists */
        assert_spin_locked(&sma->sem_perm.lock);
        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 <[email protected]>
                 */
                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);
        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;

    return 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),
              sma->sem_otime,
              sma->sem_ctime);
}
#endif