inotify: fix race

[linux-2.6.22.y-op.git] / ipc / sem.c

/*
 * linux/ipc/sem.c
 * Copyright (C) 1992 Krishna Balasubramanian
 * Copyright (C) 1995 Eric Schenk, Bruno Haible
 *
 * IMPLEMENTATION NOTES ON CODE REWRITE (Eric Schenk, January 1995):
 * This code underwent a massive rewrite in order to solve some problems
 * with the original code. In particular the original code failed to
 * wake up processes that were waiting for semval to go to 0 if the
 * value went to 0 and was then incremented rapidly enough. In solving
 * this problem I have also modified the implementation so that it
 * processes pending operations in a FIFO manner, thus give a guarantee
 * that processes waiting for a lock on the semaphore won't starve
 * unless another locking process fails to unlock.
 * In addition the following two changes in behavior have been introduced:
 * - The original implementation of semop returned the value
 *   last semaphore element examined on success. This does not
 *   match the manual page specifications, and effectively
 *   allows the user to read the semaphore even if they do not
 *   have read permissions. The implementation now returns 0
 *   on success as stated in the manual page.
 * - There is some confusion over whether the set of undo adjustments
 *   to be performed at exit should be done in an atomic manner.
 *   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.
 *   The current implementation does not do so. This is because I don't
 *   think it is the right thing (TM) to do, and because I couldn't
 *   see a clean way to get the old behavior with the new design.
 *   The POSIX standard and SVID should be consulted to determine
 *   what behavior is mandated.
 *
 * Further notes on refinement (Christoph Rohland, December 1998):
 * - The POSIX standard says, that the undo adjustments simply should
 *   redo. So the current implementation is o.K.
 * - The previous code had two flaws:
 *   1) It actively gave the semaphore to the next waiting process
 *      sleeping on the semaphore. Since this process did not have the
 *      cpu this led to many unnecessary context switches and bad
 *      performance. Now we only check which process should be able to
 *      get the semaphore and if this process wants to reduce some
 *      semaphore value we simply wake it up without doing the
 *      operation. So it has to try to get it later. Thus e.g. the
 *      running process may reacquire the semaphore during the current
 *      time slice. If it only waits for zero or increases the semaphore,
 *      we do the operation in advance and wake it up.
 *   2) It did not wake up all zero waiting processes. We try to do
 *      better but only get the semops right which only wait for zero or
 *      increase. If there are decrement operations in the operations
 *      array we do the same as before.
 *
 * With the incarnation of O(1) scheduler, it becomes unnecessary to perform
 * check/retry algorithm for waking up blocked processes as the new scheduler
 * is better at handling thread switch than the old one.
 *
 * /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 <alan@redhat.com>
 * Lockless wakeup
 * (c) 2003 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>
 */

#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/mutex.h>
#include <linux/nsproxy.h>

#include <asm/uaccess.h>
#include "util.h"

#define sem_ids(ns)     (*((ns)->ids[IPC_SEM_IDS]))

#define sem_lock(ns, id)        ((struct sem_array*)ipc_lock(&sem_ids(ns), id))
#define sem_unlock(sma)         ipc_unlock(&(sma)->sem_perm)
#define sem_rmid(ns, id)        ((struct sem_array*)ipc_rmid(&sem_ids(ns), id))
#define sem_checkid(ns, sma, semid)     \
        ipc_checkid(&sem_ids(ns),&sma->sem_perm,semid)
#define sem_buildid(ns, id, seq) \
        ipc_buildid(&sem_ids(ns), id, seq)

static struct ipc_ids init_sem_ids;

static int newary(struct ipc_namespace *, key_t, int, int);
static void freeary(struct ipc_namespace *ns, struct sem_array *sma, int id);
#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]

static void __ipc_init __sem_init_ns(struct ipc_namespace *ns, struct ipc_ids *ids)
{
        ns->ids[IPC_SEM_IDS] = ids;
        ns->sc_semmsl = SEMMSL;
        ns->sc_semmns = SEMMNS;
        ns->sc_semopm = SEMOPM;
        ns->sc_semmni = SEMMNI;
        ns->used_sems = 0;
        ipc_init_ids(ids, ns->sc_semmni);
}

#ifdef CONFIG_IPC_NS
int sem_init_ns(struct ipc_namespace *ns)
{
        struct ipc_ids *ids;

        ids = kmalloc(sizeof(struct ipc_ids), GFP_KERNEL);
        if (ids == NULL)
                return -ENOMEM;

        __sem_init_ns(ns, ids);
        return 0;
}

void sem_exit_ns(struct ipc_namespace *ns)
{
        int i;
        struct sem_array *sma;

        mutex_lock(&sem_ids(ns).mutex);
        for (i = 0; i <= sem_ids(ns).max_id; i++) {
                sma = sem_lock(ns, i);
                if (sma == NULL)
                        continue;

                freeary(ns, sma, i);
        }
        mutex_unlock(&sem_ids(ns).mutex);

        ipc_fini_ids(ns->ids[IPC_SEM_IDS]);
        kfree(ns->ids[IPC_SEM_IDS]);
        ns->ids[IPC_SEM_IDS] = NULL;
}
#endif

void __init sem_init (void)
{
        __sem_init_ns(&init_ipc_ns, &init_sem_ids);
        ipc_init_proc_interface("sysvipc/sem",
                                "       key      semid perms      nsems   uid   gid  cuid  cgid      otime      ctime\n",
                                IPC_SEM_IDS, sysvipc_sem_proc_show);
}

/*
 * 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, key_t key, int nsems, int semflg)
{
        int id;
        int retval;
        struct sem_array *sma;
        int size;

        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 == -1) {
                security_sem_free(sma);
                ipc_rcu_putref(sma);
                return -ENOSPC;
        }
        ns->used_sems += nsems;

        sma->sem_id = sem_buildid(ns, id, sma->sem_perm.seq);
        sma->sem_base = (struct sem *) &sma[1];
        /* sma->sem_pending = NULL; */
        sma->sem_pending_last = &sma->sem_pending;
        /* sma->undo = NULL; */
        sma->sem_nsems = nsems;
        sma->sem_ctime = get_seconds();
        sem_unlock(sma);

        return sma->sem_id;
}

asmlinkage long sys_semget (key_t key, int nsems, int semflg)
{
        int id, err = -EINVAL;
        struct sem_array *sma;
        struct ipc_namespace *ns;

        ns = current->nsproxy->ipc_ns;

        if (nsems < 0 || nsems > ns->sc_semmsl)
                return -EINVAL;
        mutex_lock(&sem_ids(ns).mutex);
        
        if (key == IPC_PRIVATE) {
                err = newary(ns, key, nsems, semflg);
        } else if ((id = ipc_findkey(&sem_ids(ns), key)) == -1) {  /* key not used */
                if (!(semflg & IPC_CREAT))
                        err = -ENOENT;
                else
                        err = newary(ns, key, nsems, semflg);
        } else if (semflg & IPC_CREAT && semflg & IPC_EXCL) {
                err = -EEXIST;
        } else {
                sma = sem_lock(ns, id);
                BUG_ON(sma==NULL);
                if (nsems > sma->sem_nsems)
                        err = -EINVAL;
                else if (ipcperms(&sma->sem_perm, semflg))
                        err = -EACCES;
                else {
                        int semid = sem_buildid(ns, id, sma->sem_perm.seq);
                        err = security_sem_associate(sma, semflg);
                        if (!err)
                                err = semid;
                }
                sem_unlock(sma);
        }

        mutex_unlock(&sem_ids(ns).mutex);
        return err;
}

/* Manage the doubly linked list sma->sem_pending as a FIFO:
 * insert new queue elements at the tail sma->sem_pending_last.
 */
static inline void append_to_queue (struct sem_array * sma,
                                    struct sem_queue * q)
{
        *(q->prev = sma->sem_pending_last) = q;
        *(sma->sem_pending_last = &q->next) = NULL;
}

static inline void prepend_to_queue (struct sem_array * sma,
                                     struct sem_queue * q)
{
        q->next = sma->sem_pending;
        *(q->prev = &sma->sem_pending) = q;
        if (q->next)
                q->next->prev = &q->next;
        else /* sma->sem_pending_last == &sma->sem_pending */
                sma->sem_pending_last = &q->next;
}

static inline void remove_from_queue (struct sem_array * sma,
                                      struct sem_queue * q)
{
        *(q->prev) = q->next;
        if (q->next)
                q->next->prev = q->prev;
        else /* sma->sem_pending_last == &q->next */
                sma->sem_pending_last = q->prev;
        q->prev = NULL; /* mark as removed */
}

/*
 * 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--;
        }
        
        sma->sem_otime = get_seconds();
        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;
}

/* Go through the pending queue for the indicated semaphore
 * looking for tasks that can be completed.
 */
static void update_queue (struct sem_array * sma)
{
        int error;
        struct sem_queue * q;

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

                /* Does q->sleeper still need to sleep? */
                if (error <= 0) {
                        struct sem_queue *n;
                        remove_from_queue(sma,q);
                        q->status = IN_WAKEUP;
                        /*
                         * Continue scanning. The next operation
                         * that must be checked depends on the type of the
                         * completed operation:
                         * - if the operation modified the array, then
                         *   restart from the head of the queue and
                         *   check for threads that might be waiting
                         *   for semaphore values to become 0.
                         * - if the operation didn't modify the array,
                         *   then just continue.
                         */
                        if (q->alter)
                                n = sma->sem_pending;
                        else
                                n = q->next;
                        wake_up_process(q->sleeper);
                        /* hands-off: q will disappear immediately after
                         * writing q->status.
                         */
                        smp_wmb();
                        q->status = error;
                        q = n;
                } else {
                        q = q->next;
                }
        }
}

/* 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;
        for (q = sma->sem_pending; q; q = q->next) {
                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;
        for (q = sma->sem_pending; q; q = q->next) {
                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.mutex locked and
 * the spinlock for this semaphore set hold. sem_ids.mutex remains locked
 * on exit.
 */
static void freeary (struct ipc_namespace *ns, struct sem_array *sma, int id)
{
        struct sem_undo *un;
        struct sem_queue *q;
        int size;

        /* Invalidate the existing undo structures for this semaphore set.
         * (They will be freed without any further action in exit_sem()
         * or during the next semop.)
         */
        for (un = sma->undo; un; un = un->id_next)
                un->semid = -1;

        /* Wake up all pending processes and let them fail with EIDRM. */
        q = sma->sem_pending;
        while(q) {
                struct sem_queue *n;
                /* lazy remove_from_queue: we are killing the whole queue */
                q->prev = NULL;
                n = q->next;
                q->status = IN_WAKEUP;
                wake_up_process(q->sleeper); /* doesn't sleep */
                smp_wmb();
                q->status = -EIDRM;     /* hands-off q */
                q = n;
        }

        /* Remove the semaphore set from the ID array*/
        sma = sem_rmid(ns, id);
        sem_unlock(sma);

        ns->used_sems -= sma->sem_nsems;
        size = sizeof (*sma) + sma->sem_nsems * sizeof (struct sem);
        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;

                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 semnum,
                int cmd, int version, union semun arg)
{
        int err = -EINVAL;
        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;
                mutex_lock(&sem_ids(ns).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 = sem_ids(ns).max_id;
                mutex_unlock(&sem_ids(ns).mutex);
                if (copy_to_user (arg.__buf, &seminfo, sizeof(struct seminfo))) 
                        return -EFAULT;
                return (max_id < 0) ? 0: max_id;
        }
        case SEM_STAT:
        {
                struct semid64_ds tbuf;
                int id;

                if(semid >= sem_ids(ns).entries->size)
                        return -EINVAL;

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

                sma = sem_lock(ns, semid);
                if(sma == NULL)
                        return -EINVAL;

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

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

                id = sem_buildid(ns, semid, sma->sem_perm.seq);

                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;
        }
        return err;
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;

        sma = sem_lock(ns, semid);
        if(sma==NULL)
                return -EINVAL;

        nsems = sma->sem_nsems;

        err=-EIDRM;
        if (sem_checkid(ns,sma,semid))
                goto out_unlock;

        err = -EACCES;
        if (ipcperms (&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) {
                        ipc_rcu_getref(sma);
                        sem_unlock(sma);                        

                        sem_io = ipc_alloc(sizeof(ushort)*nsems);
                        if(sem_io == NULL) {
                                ipc_lock_by_ptr(&sma->sem_perm);
                                ipc_rcu_putref(sma);
                                sem_unlock(sma);
                                return -ENOMEM;
                        }

                        ipc_lock_by_ptr(&sma->sem_perm);
                        ipc_rcu_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;

                ipc_rcu_getref(sma);
                sem_unlock(sma);

                if(nsems > SEMMSL_FAST) {
                        sem_io = ipc_alloc(sizeof(ushort)*nsems);
                        if(sem_io == NULL) {
                                ipc_lock_by_ptr(&sma->sem_perm);
                                ipc_rcu_putref(sma);
                                sem_unlock(sma);
                                return -ENOMEM;
                        }
                }

                if (copy_from_user (sem_io, arg.array, nsems*sizeof(ushort))) {
                        ipc_lock_by_ptr(&sma->sem_perm);
                        ipc_rcu_putref(sma);
                        sem_unlock(sma);
                        err = -EFAULT;
                        goto out_free;
                }

                for (i = 0; i < nsems; i++) {
                        if (sem_io[i] > SEMVMX) {
                                ipc_lock_by_ptr(&sma->sem_perm);
                                ipc_rcu_putref(sma);
                                sem_unlock(sma);
                                err = -ERANGE;
                                goto out_free;
                        }
                }
                ipc_lock_by_ptr(&sma->sem_perm);
                ipc_rcu_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];
                for (un = sma->undo; un; un = un->id_next)
                        for (i = 0; i < nsems; i++)
                                un->semadj[i] = 0;
                sma->sem_ctime = get_seconds();
                /* maybe some queued-up processes were waiting for this */
                update_queue(sma);
                err = 0;
                goto out_unlock;
        }
        case IPC_STAT:
        {
                struct semid64_ds tbuf;
                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 0;
        }
        /* 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;

                for (un = sma->undo; un; un = un->id_next)
                        un->semadj[semnum] = 0;
                curr->semval = val;
                curr->sempid = current->tgid;
                sma->sem_ctime = get_seconds();
                /* maybe some queued-up processes were waiting for this */
                update_queue(sma);
                err = 0;
                goto out_unlock;
        }
        }
out_unlock:
        sem_unlock(sma);
out_free:
        if(sem_io != fast_sem_io)
                ipc_free(sem_io, sizeof(ushort)*nsems);
        return err;
}

struct sem_setbuf {
        uid_t   uid;
        gid_t   gid;
        mode_t  mode;
};

static inline unsigned long copy_semid_from_user(struct sem_setbuf *out, void __user *buf, int version)
{
        switch(version) {
        case IPC_64:
            {
                struct semid64_ds tbuf;

                if(copy_from_user(&tbuf, buf, sizeof(tbuf)))
                        return -EFAULT;

                out->uid        = tbuf.sem_perm.uid;
                out->gid        = tbuf.sem_perm.gid;
                out->mode       = tbuf.sem_perm.mode;

                return 0;
            }
        case IPC_OLD:
            {
                struct semid_ds tbuf_old;

                if(copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
                        return -EFAULT;

                out->uid        = tbuf_old.sem_perm.uid;
                out->gid        = tbuf_old.sem_perm.gid;
                out->mode       = tbuf_old.sem_perm.mode;

                return 0;
            }
        default:
                return -EINVAL;
        }
}

static int semctl_down(struct ipc_namespace *ns, int semid, int semnum,
                int cmd, int version, union semun arg)
{
        struct sem_array *sma;
        int err;
        struct sem_setbuf setbuf;
        struct kern_ipc_perm *ipcp;

        if(cmd == IPC_SET) {
                if(copy_semid_from_user (&setbuf, arg.buf, version))
                        return -EFAULT;
        }
        sma = sem_lock(ns, semid);
        if(sma==NULL)
                return -EINVAL;

        if (sem_checkid(ns,sma,semid)) {
                err=-EIDRM;
                goto out_unlock;
        }       
        ipcp = &sma->sem_perm;

        err = audit_ipc_obj(ipcp);
        if (err)
                goto out_unlock;

        if (cmd == IPC_SET) {
                err = audit_ipc_set_perm(0, setbuf.uid, setbuf.gid, setbuf.mode);
                if (err)
                        goto out_unlock;
        }
        if (current->euid != ipcp->cuid && 
            current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN)) {
                err=-EPERM;
                goto out_unlock;
        }

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

        switch(cmd){
        case IPC_RMID:
                freeary(ns, sma, semid);
                err = 0;
                break;
        case IPC_SET:
                ipcp->uid = setbuf.uid;
                ipcp->gid = setbuf.gid;
                ipcp->mode = (ipcp->mode & ~S_IRWXUGO)
                                | (setbuf.mode & S_IRWXUGO);
                sma->sem_ctime = get_seconds();
                sem_unlock(sma);
                err = 0;
                break;
        default:
                sem_unlock(sma);
                err = -EINVAL;
                break;
        }
        return err;

out_unlock:
        sem_unlock(sma);
        return err;
}

asmlinkage long sys_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 SEM_STAT:
                err = semctl_nolock(ns,semid,semnum,cmd,version,arg);
                return err;
        case GETALL:
        case GETVAL:
        case GETPID:
        case GETNCNT:
        case GETZCNT:
        case IPC_STAT:
        case SETVAL:
        case SETALL:
                err = semctl_main(ns,semid,semnum,cmd,version,arg);
                return err;
        case IPC_RMID:
        case IPC_SET:
                mutex_lock(&sem_ids(ns).mutex);
                err = semctl_down(ns,semid,semnum,cmd,version,arg);
                mutex_unlock(&sem_ids(ns).mutex);
                return err;
        default:
                return -EINVAL;
        }
}

static inline void lock_semundo(void)
{
        struct sem_undo_list *undo_list;

        undo_list = current->sysvsem.undo_list;
        if (undo_list)
                spin_lock(&undo_list->lock);
}

/* This code has an interaction with copy_semundo().
 * Consider; two tasks are sharing the undo_list. task1
 * acquires the undo_list lock in lock_semundo().  If task2 now
 * exits before task1 releases the lock (by calling
 * unlock_semundo()), then task1 will never call spin_unlock().
 * This leave the sem_undo_list in a locked state.  If task1 now creats task3
 * and once again shares the sem_undo_list, the sem_undo_list will still be
 * locked, and future SEM_UNDO operations will deadlock.  This case is
 * dealt with in copy_semundo() by having it reinitialize the spin lock when 
 * the refcnt goes from 1 to 2.
 */
static inline void unlock_semundo(void)
{
        struct sem_undo_list *undo_list;

        undo_list = current->sysvsem.undo_list;
        if (undo_list)
                spin_unlock(&undo_list->lock);
}


/* 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);
                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 **last, *un;

        last = &ulp->proc_list;
        un = *last;
        while(un != NULL) {
                if(un->semid==semid)
                        break;
                if(un->semid==-1) {
                        *last=un->proc_next;
                        kfree(un);
                } else {
                        last=&un->proc_next;
                }
                un=*last;
        }
        return un;
}

static struct sem_undo *find_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);

        lock_semundo();
        un = lookup_undo(ulp, semid);
        unlock_semundo();
        if (likely(un!=NULL))
                goto out;

        /* no undo structure around - allocate one. */
        sma = sem_lock(ns, semid);
        un = ERR_PTR(-EINVAL);
        if(sma==NULL)
                goto out;
        un = ERR_PTR(-EIDRM);
        if (sem_checkid(ns,sma,semid)) {
                sem_unlock(sma);
                goto out;
        }
        nsems = sma->sem_nsems;
        ipc_rcu_getref(sma);
        sem_unlock(sma);

        new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
        if (!new) {
                ipc_lock_by_ptr(&sma->sem_perm);
                ipc_rcu_putref(sma);
                sem_unlock(sma);
                return ERR_PTR(-ENOMEM);
        }
        new->semadj = (short *) &new[1];
        new->semid = semid;

        lock_semundo();
        un = lookup_undo(ulp, semid);
        if (un) {
                unlock_semundo();
                kfree(new);
                ipc_lock_by_ptr(&sma->sem_perm);
                ipc_rcu_putref(sma);
                sem_unlock(sma);
                goto out;
        }
        ipc_lock_by_ptr(&sma->sem_perm);
        ipc_rcu_putref(sma);
        if (sma->sem_perm.deleted) {
                sem_unlock(sma);
                unlock_semundo();
                kfree(new);
                un = ERR_PTR(-EIDRM);
                goto out;
        }
        new->proc_next = ulp->proc_list;
        ulp->proc_list = new;
        new->id_next = sma->undo;
        sma->undo = new;
        sem_unlock(sma);
        un = new;
        unlock_semundo();
out:
        return un;
}

asmlinkage long sys_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;

        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;
        }

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

        sma = sem_lock(ns, semid);
        error=-EINVAL;
        if(sma==NULL)
                goto out_free;
        error = -EIDRM;
        if (sem_checkid(ns,sma,semid))
                goto out_unlock_free;
        /*
         * semid identifies are not unique - find_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 retry.
         */
        if (un && un->semid == -1) {
                sem_unlock(sma);
                goto retry_undos;
        }
        error = -EFBIG;
        if (max >= sma->sem_nsems)
                goto out_unlock_free;

        error = -EACCES;
        if (ipcperms(&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, current->tgid);
        if (error <= 0) {
                if (alter && error == 0)
                        update_queue (sma);
                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.sma = sma;
        queue.sops = sops;
        queue.nsops = nsops;
        queue.undo = un;
        queue.pid = current->tgid;
        queue.id = semid;
        queue.alter = alter;
        if (alter)
                append_to_queue(sma ,&queue);
        else
                prepend_to_queue(sma ,&queue);

        queue.status = -EINTR;
        queue.sleeper = current;
        current->state = TASK_INTERRUPTIBLE;
        sem_unlock(sma);

        if (timeout)
                jiffies_left = schedule_timeout(jiffies_left);
        else
                schedule();

        error = queue.status;
        while(unlikely(error == IN_WAKEUP)) {
                cpu_relax();
                error = queue.status;
        }

        if (error != -EINTR) {
                /* fast path: update_queue already obtained all requested
                 * resources */
                goto out_free;
        }

        sma = sem_lock(ns, semid);
        if(sma==NULL) {
                BUG_ON(queue.prev != NULL);
                error = -EIDRM;
                goto out_free;
        }

        /*
         * If queue.status != -EINTR we are woken up by another process
         */
        error = queue.status;
        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;
        remove_from_queue(sma,&queue);
        goto out_unlock_free;

out_unlock_free:
        sem_unlock(sma);
out_free:
        if(sops != fast_sops)
                kfree(sops);
        return error;
}

asmlinkage long sys_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.
 *
 * See the notes above unlock_semundo() regarding the spin_lock_init()
 * in this code.  Initialize the undo_list->lock here instead of get_undo_list()
 * because of the reasoning in the comment above unlock_semundo.
 */

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 *undo_list;
        struct sem_undo *u, **up;
        struct ipc_namespace *ns;

        undo_list = tsk->sysvsem.undo_list;
        if (!undo_list)
                return;

        if (!atomic_dec_and_test(&undo_list->refcnt))
                return;

        ns = tsk->nsproxy->ipc_ns;
        /* There's no need to hold the semundo list lock, as current
         * is the last task exiting for this undo list.
         */
        for (up = &undo_list->proc_list; (u = *up); *up = u->proc_next, kfree(u)) {
                struct sem_array *sma;
                int nsems, i;
                struct sem_undo *un, **unp;
                int semid;
               
                semid = u->semid;

                if(semid == -1)
                        continue;
                sma = sem_lock(ns, semid);
                if (sma == NULL)
                        continue;

                if (u->semid == -1)
                        goto next_entry;

                BUG_ON(sem_checkid(ns,sma,u->semid));

                /* remove u from the sma->undo list */
                for (unp = &sma->undo; (un = *unp); unp = &un->id_next) {
                        if (u == un)
                                goto found;
                }
                printk ("exit_sem undo list error id=%d\n", u->semid);
                goto next_entry;
found:
                *unp = un->id_next;
                /* perform adjustments registered in u */
                nsems = sma->sem_nsems;
                for (i = 0; i < nsems; i++) {
                        struct sem * semaphore = &sma->sem_base[i];
                        if (u->semadj[i]) {
                                semaphore->semval += u->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 = current->tgid;
                        }
                }
                sma->sem_otime = get_seconds();
                /* maybe some queued-up processes were waiting for this */
                update_queue(sma);
next_entry:
                sem_unlock(sma);
        }
        kfree(undo_list);
}

#ifdef CONFIG_PROC_FS
static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
{
        struct sem_array *sma = it;

        return seq_printf(s,
                          "%10d %10d  %4o %10lu %5u %5u %5u %5u %10lu %10lu\n",
                          sma->sem_perm.key,
                          sma->sem_id,
                          sma->sem_perm.mode,
                          sma->sem_nsems,
                          sma->sem_perm.uid,
                          sma->sem_perm.gid,
                          sma->sem_perm.cuid,
                          sma->sem_perm.cgid,
                          sma->sem_otime,
                          sma->sem_ctime);
}
#endif