Now it works.

[cbs-scheduler.git] / ipc / msg.c

/*
 * linux/ipc/msg.c
 * Copyright (C) 1992 Krishna Balasubramanian
 *
 * Removed all the remaining kerneld mess
 * Catch the -EFAULT stuff properly
 * Use GFP_KERNEL for messages as in 1.2
 * Fixed up the unchecked user space derefs
 * Copyright (C) 1998 Alan Cox & Andi Kleen
 *
 * /proc/sysvipc/msg support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
 *
 * mostly rewritten, threaded and wake-one semantics added
 * MSGMAX limit removed, sysctl's added
 * (c) 1999 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/capability.h>
#include <linux/slab.h>
#include <linux/msg.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/proc_fs.h>
#include <linux/list.h>
#include <linux/security.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/seq_file.h>
#include <linux/rwsem.h>
#include <linux/nsproxy.h>
#include <linux/ipc_namespace.h>

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

/*
 * one msg_receiver structure for each sleeping receiver:
 */
struct msg_receiver {
        struct list_head        r_list;
        struct task_struct      *r_tsk;

        int                     r_mode;
        long                    r_msgtype;
        long                    r_maxsize;

        struct msg_msg          *volatile r_msg;
};

/* one msg_sender for each sleeping sender */
struct msg_sender {
        struct list_head        list;
        struct task_struct      *tsk;
};

#define SEARCH_ANY              1
#define SEARCH_EQUAL            2
#define SEARCH_NOTEQUAL         3
#define SEARCH_LESSEQUAL        4

#define msg_ids(ns)     ((ns)->ids[IPC_MSG_IDS])

#define msg_unlock(msq)         ipc_unlock(&(msq)->q_perm)

static void freeque(struct ipc_namespace *, struct kern_ipc_perm *);
static int newque(struct ipc_namespace *, struct ipc_params *);
#ifdef CONFIG_PROC_FS
static int sysvipc_msg_proc_show(struct seq_file *s, void *it);
#endif

/*
 * Scale msgmni with the available lowmem size: the memory dedicated to msg
 * queues should occupy at most 1/MSG_MEM_SCALE of lowmem.
 * Also take into account the number of nsproxies created so far.
 * This should be done staying within the (MSGMNI , IPCMNI/nr_ipc_ns) range.
 */
void recompute_msgmni(struct ipc_namespace *ns)
{
        struct sysinfo i;
        unsigned long allowed;
        int nb_ns;

        si_meminfo(&i);
        allowed = (((i.totalram - i.totalhigh) / MSG_MEM_SCALE) * i.mem_unit)
                / MSGMNB;
        nb_ns = atomic_read(&nr_ipc_ns);
        allowed /= nb_ns;

        if (allowed < MSGMNI) {
                ns->msg_ctlmni = MSGMNI;
                return;
        }

        if (allowed > IPCMNI / nb_ns) {
                ns->msg_ctlmni = IPCMNI / nb_ns;
                return;
        }

        ns->msg_ctlmni = allowed;
}

void msg_init_ns(struct ipc_namespace *ns)
{
        ns->msg_ctlmax = MSGMAX;
        ns->msg_ctlmnb = MSGMNB;

        recompute_msgmni(ns);

        atomic_set(&ns->msg_bytes, 0);
        atomic_set(&ns->msg_hdrs, 0);
        ipc_init_ids(&ns->ids[IPC_MSG_IDS]);
}

#ifdef CONFIG_IPC_NS
void msg_exit_ns(struct ipc_namespace *ns)
{
        free_ipcs(ns, &msg_ids(ns), freeque);
}
#endif

void __init msg_init(void)
{
        msg_init_ns(&init_ipc_ns);

        printk(KERN_INFO "msgmni has been set to %d\n",
                init_ipc_ns.msg_ctlmni);

        ipc_init_proc_interface("sysvipc/msg",
                                "       key      msqid perms      cbytes       qnum lspid lrpid   uid   gid  cuid  cgid      stime      rtime      ctime\n",
                                IPC_MSG_IDS, sysvipc_msg_proc_show);
}

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

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

        return container_of(ipcp, struct msg_queue, q_perm);
}

static inline struct msg_queue *msg_lock_check(struct ipc_namespace *ns,
                                                int id)
{
        struct kern_ipc_perm *ipcp = ipc_lock_check(&msg_ids(ns), id);

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

        return container_of(ipcp, struct msg_queue, q_perm);
}

static inline void msg_rmid(struct ipc_namespace *ns, struct msg_queue *s)
{
        ipc_rmid(&msg_ids(ns), &s->q_perm);
}

/**
 * newque - Create a new msg queue
 * @ns: namespace
 * @params: ptr to the structure that contains the key and msgflg
 *
 * Called with msg_ids.rw_mutex held (writer)
 */
static int newque(struct ipc_namespace *ns, struct ipc_params *params)
{
        struct msg_queue *msq;
        int id, retval;
        key_t key = params->key;
        int msgflg = params->flg;

        msq = ipc_rcu_alloc(sizeof(*msq));
        if (!msq)
                return -ENOMEM;

        msq->q_perm.mode = msgflg & S_IRWXUGO;
        msq->q_perm.key = key;

        msq->q_perm.security = NULL;
        retval = security_msg_queue_alloc(msq);
        if (retval) {
                ipc_rcu_putref(msq);
                return retval;
        }

        /*
         * ipc_addid() locks msq
         */
        id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
        if (id < 0) {
                security_msg_queue_free(msq);
                ipc_rcu_putref(msq);
                return id;
        }

        msq->q_stime = msq->q_rtime = 0;
        msq->q_ctime = get_seconds();
        msq->q_cbytes = msq->q_qnum = 0;
        msq->q_qbytes = ns->msg_ctlmnb;
        msq->q_lspid = msq->q_lrpid = 0;
        INIT_LIST_HEAD(&msq->q_messages);
        INIT_LIST_HEAD(&msq->q_receivers);
        INIT_LIST_HEAD(&msq->q_senders);

        msg_unlock(msq);

        return msq->q_perm.id;
}

static inline void ss_add(struct msg_queue *msq, struct msg_sender *mss)
{
        mss->tsk = current;
        current->state = TASK_INTERRUPTIBLE;
        list_add_tail(&mss->list, &msq->q_senders);
}

static inline void ss_del(struct msg_sender *mss)
{
        if (mss->list.next != NULL)
                list_del(&mss->list);
}

static void ss_wakeup(struct list_head *h, int kill)
{
        struct list_head *tmp;

        tmp = h->next;
        while (tmp != h) {
                struct msg_sender *mss;

                mss = list_entry(tmp, struct msg_sender, list);
                tmp = tmp->next;
                if (kill)
                        mss->list.next = NULL;
                wake_up_process(mss->tsk);
        }
}

static void expunge_all(struct msg_queue *msq, int res)
{
        struct list_head *tmp;

        tmp = msq->q_receivers.next;
        while (tmp != &msq->q_receivers) {
                struct msg_receiver *msr;

                /*
                 * Make sure that the wakeup doesnt preempt
                 * this CPU prematurely. (on PREEMPT_RT)
                 */
                preempt_disable();

                msr = list_entry(tmp, struct msg_receiver, r_list);
                tmp = tmp->next;
                msr->r_msg = NULL;
                wake_up_process(msr->r_tsk); /* serializes */
                msr->r_msg = ERR_PTR(res);

                preempt_enable();
        }
}

/*
 * freeque() wakes up waiters on the sender and receiver waiting queue,
 * removes the message queue from message queue ID IDR, and cleans up all the
 * messages associated with this queue.
 *
 * msg_ids.rw_mutex (writer) and the spinlock for this message queue are held
 * before freeque() is called. msg_ids.rw_mutex remains locked on exit.
 */
static void freeque(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
{
        struct list_head *tmp;
        struct msg_queue *msq = container_of(ipcp, struct msg_queue, q_perm);

        expunge_all(msq, -EIDRM);
        ss_wakeup(&msq->q_senders, 1);
        msg_rmid(ns, msq);
        msg_unlock(msq);

        tmp = msq->q_messages.next;
        while (tmp != &msq->q_messages) {
                struct msg_msg *msg = list_entry(tmp, struct msg_msg, m_list);

                tmp = tmp->next;
                atomic_dec(&ns->msg_hdrs);
                free_msg(msg);
        }
        atomic_sub(msq->q_cbytes, &ns->msg_bytes);
        security_msg_queue_free(msq);
        ipc_rcu_putref(msq);
}

/*
 * Called with msg_ids.rw_mutex and ipcp locked.
 */
static inline int msg_security(struct kern_ipc_perm *ipcp, int msgflg)
{
        struct msg_queue *msq = container_of(ipcp, struct msg_queue, q_perm);

        return security_msg_queue_associate(msq, msgflg);
}

SYSCALL_DEFINE2(msgget, key_t, key, int, msgflg)
{
        struct ipc_namespace *ns;
        struct ipc_ops msg_ops;
        struct ipc_params msg_params;

        ns = current->nsproxy->ipc_ns;

        msg_ops.getnew = newque;
        msg_ops.associate = msg_security;
        msg_ops.more_checks = NULL;

        msg_params.key = key;
        msg_params.flg = msgflg;

        return ipcget(ns, &msg_ids(ns), &msg_ops, &msg_params);
}

static inline unsigned long
copy_msqid_to_user(void __user *buf, struct msqid64_ds *in, int version)
{
        switch(version) {
        case IPC_64:
                return copy_to_user(buf, in, sizeof(*in));
        case IPC_OLD:
        {
                struct msqid_ds out;

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

                ipc64_perm_to_ipc_perm(&in->msg_perm, &out.msg_perm);

                out.msg_stime           = in->msg_stime;
                out.msg_rtime           = in->msg_rtime;
                out.msg_ctime           = in->msg_ctime;

                if (in->msg_cbytes > USHORT_MAX)
                        out.msg_cbytes  = USHORT_MAX;
                else
                        out.msg_cbytes  = in->msg_cbytes;
                out.msg_lcbytes         = in->msg_cbytes;

                if (in->msg_qnum > USHORT_MAX)
                        out.msg_qnum    = USHORT_MAX;
                else
                        out.msg_qnum    = in->msg_qnum;

                if (in->msg_qbytes > USHORT_MAX)
                        out.msg_qbytes  = USHORT_MAX;
                else
                        out.msg_qbytes  = in->msg_qbytes;
                out.msg_lqbytes         = in->msg_qbytes;

                out.msg_lspid           = in->msg_lspid;
                out.msg_lrpid           = in->msg_lrpid;

                return copy_to_user(buf, &out, sizeof(out));
        }
        default:
                return -EINVAL;
        }
}

static inline unsigned long
copy_msqid_from_user(struct msqid64_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 msqid_ds tbuf_old;

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

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

                if (tbuf_old.msg_qbytes == 0)
                        out->msg_qbytes = tbuf_old.msg_lqbytes;
                else
                        out->msg_qbytes = tbuf_old.msg_qbytes;

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

/*
 * This function handles some msgctl 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 msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
                       struct msqid_ds __user *buf, int version)
{
        struct kern_ipc_perm *ipcp;
        struct msqid64_ds msqid64;
        struct msg_queue *msq;
        int err;

        if (cmd == IPC_SET) {
                if (copy_msqid_from_user(&msqid64, buf, version))
                        return -EFAULT;
        }

        ipcp = ipcctl_pre_down(&msg_ids(ns), msqid, cmd,
                               &msqid64.msg_perm, msqid64.msg_qbytes);
        if (IS_ERR(ipcp))
                return PTR_ERR(ipcp);

        msq = container_of(ipcp, struct msg_queue, q_perm);

        err = security_msg_queue_msgctl(msq, cmd);
        if (err)
                goto out_unlock;

        switch (cmd) {
        case IPC_RMID:
                freeque(ns, ipcp);
                goto out_up;
        case IPC_SET:
                if (msqid64.msg_qbytes > ns->msg_ctlmnb &&
                    !capable(CAP_SYS_RESOURCE)) {
                        err = -EPERM;
                        goto out_unlock;
                }

                msq->q_qbytes = msqid64.msg_qbytes;

                ipc_update_perm(&msqid64.msg_perm, ipcp);
                msq->q_ctime = get_seconds();
                /* sleeping receivers might be excluded by
                 * stricter permissions.
                 */
                expunge_all(msq, -EAGAIN);
                /* sleeping senders might be able to send
                 * due to a larger queue size.
                 */
                ss_wakeup(&msq->q_senders, 0);
                break;
        default:
                err = -EINVAL;
        }
out_unlock:
        msg_unlock(msq);
out_up:
        up_write(&msg_ids(ns).rw_mutex);
        return err;
}

SYSCALL_DEFINE3(msgctl, int, msqid, int, cmd, struct msqid_ds __user *, buf)
{
        struct msg_queue *msq;
        int err, version;
        struct ipc_namespace *ns;

        if (msqid < 0 || cmd < 0)
                return -EINVAL;

        version = ipc_parse_version(&cmd);
        ns = current->nsproxy->ipc_ns;

        switch (cmd) {
        case IPC_INFO:
        case MSG_INFO:
        {
                struct msginfo msginfo;
                int max_id;

                if (!buf)
                        return -EFAULT;
                /*
                 * We must not return kernel stack data.
                 * due to padding, it's not enough
                 * to set all member fields.
                 */
                err = security_msg_queue_msgctl(NULL, cmd);
                if (err)
                        return err;

                memset(&msginfo, 0, sizeof(msginfo));
                msginfo.msgmni = ns->msg_ctlmni;
                msginfo.msgmax = ns->msg_ctlmax;
                msginfo.msgmnb = ns->msg_ctlmnb;
                msginfo.msgssz = MSGSSZ;
                msginfo.msgseg = MSGSEG;
                down_read(&msg_ids(ns).rw_mutex);
                if (cmd == MSG_INFO) {
                        msginfo.msgpool = msg_ids(ns).in_use;
                        msginfo.msgmap = atomic_read(&ns->msg_hdrs);
                        msginfo.msgtql = atomic_read(&ns->msg_bytes);
                } else {
                        msginfo.msgmap = MSGMAP;
                        msginfo.msgpool = MSGPOOL;
                        msginfo.msgtql = MSGTQL;
                }
                max_id = ipc_get_maxid(&msg_ids(ns));
                up_read(&msg_ids(ns).rw_mutex);
                if (copy_to_user(buf, &msginfo, sizeof(struct msginfo)))
                        return -EFAULT;
                return (max_id < 0) ? 0 : max_id;
        }
        case MSG_STAT:  /* msqid is an index rather than a msg queue id */
        case IPC_STAT:
        {
                struct msqid64_ds tbuf;
                int success_return;

                if (!buf)
                        return -EFAULT;

                if (cmd == MSG_STAT) {
                        msq = msg_lock(ns, msqid);
                        if (IS_ERR(msq))
                                return PTR_ERR(msq);
                        success_return = msq->q_perm.id;
                } else {
                        msq = msg_lock_check(ns, msqid);
                        if (IS_ERR(msq))
                                return PTR_ERR(msq);
                        success_return = 0;
                }
                err = -EACCES;
                if (ipcperms(&msq->q_perm, S_IRUGO))
                        goto out_unlock;

                err = security_msg_queue_msgctl(msq, cmd);
                if (err)
                        goto out_unlock;

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

                kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
                tbuf.msg_stime  = msq->q_stime;
                tbuf.msg_rtime  = msq->q_rtime;
                tbuf.msg_ctime  = msq->q_ctime;
                tbuf.msg_cbytes = msq->q_cbytes;
                tbuf.msg_qnum   = msq->q_qnum;
                tbuf.msg_qbytes = msq->q_qbytes;
                tbuf.msg_lspid  = msq->q_lspid;
                tbuf.msg_lrpid  = msq->q_lrpid;
                msg_unlock(msq);
                if (copy_msqid_to_user(buf, &tbuf, version))
                        return -EFAULT;
                return success_return;
        }
        case IPC_SET:
        case IPC_RMID:
                err = msgctl_down(ns, msqid, cmd, buf, version);
                return err;
        default:
                return  -EINVAL;
        }

out_unlock:
        msg_unlock(msq);
        return err;
}

static int testmsg(struct msg_msg *msg, long type, int mode)
{
        switch(mode)
        {
                case SEARCH_ANY:
                        return 1;
                case SEARCH_LESSEQUAL:
                        if (msg->m_type <=type)
                                return 1;
                        break;
                case SEARCH_EQUAL:
                        if (msg->m_type == type)
                                return 1;
                        break;
                case SEARCH_NOTEQUAL:
                        if (msg->m_type != type)
                                return 1;
                        break;
        }
        return 0;
}

static inline int pipelined_send(struct msg_queue *msq, struct msg_msg *msg)
{
        struct list_head *tmp;

        tmp = msq->q_receivers.next;
        while (tmp != &msq->q_receivers) {
                struct msg_receiver *msr;

                msr = list_entry(tmp, struct msg_receiver, r_list);
                tmp = tmp->next;
                if (testmsg(msg, msr->r_msgtype, msr->r_mode) &&
                    !security_msg_queue_msgrcv(msq, msg, msr->r_tsk,
                                               msr->r_msgtype, msr->r_mode)) {

                        /*
                         * Make sure that the wakeup doesnt preempt
                         * this CPU prematurely. (on PREEMPT_RT)
                         */
                        preempt_disable();

                        list_del(&msr->r_list);
                        if (msr->r_maxsize < msg->m_ts) {
                                msr->r_msg = NULL;
                                wake_up_process(msr->r_tsk); /* serializes */
                                msr->r_msg = ERR_PTR(-E2BIG);
                        } else {
                                msr->r_msg = NULL;
                                msq->q_lrpid = task_pid_vnr(msr->r_tsk);
                                msq->q_rtime = get_seconds();
                                wake_up_process(msr->r_tsk); /* serializes */
                                msr->r_msg = msg;
                                preempt_enable();

                                return 1;
                        }
                        preempt_enable();
                }
        }
        return 0;
}

long do_msgsnd(int msqid, long mtype, void __user *mtext,
                size_t msgsz, int msgflg)
{
        struct msg_queue *msq;
        struct msg_msg *msg;
        int err;
        struct ipc_namespace *ns;

        ns = current->nsproxy->ipc_ns;

        if (msgsz > ns->msg_ctlmax || (long) msgsz < 0 || msqid < 0)
                return -EINVAL;
        if (mtype < 1)
                return -EINVAL;

        msg = load_msg(mtext, msgsz);
        if (IS_ERR(msg))
                return PTR_ERR(msg);

        msg->m_type = mtype;
        msg->m_ts = msgsz;

        msq = msg_lock_check(ns, msqid);
        if (IS_ERR(msq)) {
                err = PTR_ERR(msq);
                goto out_free;
        }

        for (;;) {
                struct msg_sender s;

                err = -EACCES;
                if (ipcperms(&msq->q_perm, S_IWUGO))
                        goto out_unlock_free;

                err = security_msg_queue_msgsnd(msq, msg, msgflg);
                if (err)
                        goto out_unlock_free;

                if (msgsz + msq->q_cbytes <= msq->q_qbytes &&
                                1 + msq->q_qnum <= msq->q_qbytes) {
                        break;
                }

                /* queue full, wait: */
                if (msgflg & IPC_NOWAIT) {
                        err = -EAGAIN;
                        goto out_unlock_free;
                }
                ss_add(msq, &s);
                ipc_rcu_getref(msq);
                msg_unlock(msq);
                schedule();

                ipc_lock_by_ptr(&msq->q_perm);
                ipc_rcu_putref(msq);
                if (msq->q_perm.deleted) {
                        err = -EIDRM;
                        goto out_unlock_free;
                }
                ss_del(&s);

                if (signal_pending(current)) {
                        err = -ERESTARTNOHAND;
                        goto out_unlock_free;
                }
        }

        msq->q_lspid = task_tgid_vnr(current);
        msq->q_stime = get_seconds();

        if (!pipelined_send(msq, msg)) {
                /* noone is waiting for this message, enqueue it */
                list_add_tail(&msg->m_list, &msq->q_messages);
                msq->q_cbytes += msgsz;
                msq->q_qnum++;
                atomic_add(msgsz, &ns->msg_bytes);
                atomic_inc(&ns->msg_hdrs);
        }

        err = 0;
        msg = NULL;

out_unlock_free:
        msg_unlock(msq);
out_free:
        if (msg != NULL)
                free_msg(msg);
        return err;
}

SYSCALL_DEFINE4(msgsnd, int, msqid, struct msgbuf __user *, msgp, size_t, msgsz,
                int, msgflg)
{
        long mtype;

        if (get_user(mtype, &msgp->mtype))
                return -EFAULT;
        return do_msgsnd(msqid, mtype, msgp->mtext, msgsz, msgflg);
}

static inline int convert_mode(long *msgtyp, int msgflg)
{
        /*
         *  find message of correct type.
         *  msgtyp = 0 => get first.
         *  msgtyp > 0 => get first message of matching type.
         *  msgtyp < 0 => get message with least type must be < abs(msgtype).
         */
        if (*msgtyp == 0)
                return SEARCH_ANY;
        if (*msgtyp < 0) {
                *msgtyp = -*msgtyp;
                return SEARCH_LESSEQUAL;
        }
        if (msgflg & MSG_EXCEPT)
                return SEARCH_NOTEQUAL;
        return SEARCH_EQUAL;
}

long do_msgrcv(int msqid, long *pmtype, void __user *mtext,
                size_t msgsz, long msgtyp, int msgflg)
{
        struct msg_queue *msq;
        struct msg_msg *msg;
        int mode;
        struct ipc_namespace *ns;

        if (msqid < 0 || (long) msgsz < 0)
                return -EINVAL;
        mode = convert_mode(&msgtyp, msgflg);
        ns = current->nsproxy->ipc_ns;

        msq = msg_lock_check(ns, msqid);
        if (IS_ERR(msq))
                return PTR_ERR(msq);

        for (;;) {
                struct msg_receiver msr_d;
                struct list_head *tmp;

                msg = ERR_PTR(-EACCES);
                if (ipcperms(&msq->q_perm, S_IRUGO))
                        goto out_unlock;

                msg = ERR_PTR(-EAGAIN);
                tmp = msq->q_messages.next;
                while (tmp != &msq->q_messages) {
                        struct msg_msg *walk_msg;

                        walk_msg = list_entry(tmp, struct msg_msg, m_list);
                        if (testmsg(walk_msg, msgtyp, mode) &&
                            !security_msg_queue_msgrcv(msq, walk_msg, current,
                                                       msgtyp, mode)) {

                                msg = walk_msg;
                                if (mode == SEARCH_LESSEQUAL &&
                                                walk_msg->m_type != 1) {
                                        msg = walk_msg;
                                        msgtyp = walk_msg->m_type - 1;
                                } else {
                                        msg = walk_msg;
                                        break;
                                }
                        }
                        tmp = tmp->next;
                }
                if (!IS_ERR(msg)) {
                        /*
                         * Found a suitable message.
                         * Unlink it from the queue.
                         */
                        if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
                                msg = ERR_PTR(-E2BIG);
                                goto out_unlock;
                        }
                        list_del(&msg->m_list);
                        msq->q_qnum--;
                        msq->q_rtime = get_seconds();
                        msq->q_lrpid = task_tgid_vnr(current);
                        msq->q_cbytes -= msg->m_ts;
                        atomic_sub(msg->m_ts, &ns->msg_bytes);
                        atomic_dec(&ns->msg_hdrs);
                        ss_wakeup(&msq->q_senders, 0);
                        msg_unlock(msq);
                        break;
                }
                /* No message waiting. Wait for a message */
                if (msgflg & IPC_NOWAIT) {
                        msg = ERR_PTR(-ENOMSG);
                        goto out_unlock;
                }
                list_add_tail(&msr_d.r_list, &msq->q_receivers);
                msr_d.r_tsk = current;
                msr_d.r_msgtype = msgtyp;
                msr_d.r_mode = mode;
                if (msgflg & MSG_NOERROR)
                        msr_d.r_maxsize = INT_MAX;
                else
                        msr_d.r_maxsize = msgsz;
                msr_d.r_msg = ERR_PTR(-EAGAIN);
                current->state = TASK_INTERRUPTIBLE;
                msg_unlock(msq);

                schedule();

                /* Lockless receive, part 1:
                 * Disable preemption.  We don't hold a reference to the queue
                 * and getting a reference would defeat the idea of a lockless
                 * operation, thus the code relies on rcu to guarantee the
                 * existance of msq:
                 * Prior to destruction, expunge_all(-EIRDM) changes r_msg.
                 * Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
                 * rcu_read_lock() prevents preemption between reading r_msg
                 * and the spin_lock() inside ipc_lock_by_ptr().
                 */
                rcu_read_lock();

                /* Lockless receive, part 2:
                 * Wait until pipelined_send or expunge_all are outside of
                 * wake_up_process(). There is a race with exit(), see
                 * ipc/mqueue.c for the details.
                 */
                msg = (struct msg_msg*)msr_d.r_msg;
                while (msg == NULL) {
                        cpu_relax();
                        msg = (struct msg_msg *)msr_d.r_msg;
                }

                /* Lockless receive, part 3:
                 * If there is a message or an error then accept it without
                 * locking.
                 */
                if (msg != ERR_PTR(-EAGAIN)) {
                        rcu_read_unlock();
                        break;
                }

                /* Lockless receive, part 3:
                 * Acquire the queue spinlock.
                 */
                ipc_lock_by_ptr(&msq->q_perm);
                rcu_read_unlock();

                /* Lockless receive, part 4:
                 * Repeat test after acquiring the spinlock.
                 */
                msg = (struct msg_msg*)msr_d.r_msg;
                if (msg != ERR_PTR(-EAGAIN))
                        goto out_unlock;

                list_del(&msr_d.r_list);
                if (signal_pending(current)) {
                        msg = ERR_PTR(-ERESTARTNOHAND);
out_unlock:
                        msg_unlock(msq);
                        break;
                }
        }
        if (IS_ERR(msg))
                return PTR_ERR(msg);

        msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
        *pmtype = msg->m_type;
        if (store_msg(mtext, msg, msgsz))
                msgsz = -EFAULT;

        free_msg(msg);

        return msgsz;
}

SYSCALL_DEFINE5(msgrcv, int, msqid, struct msgbuf __user *, msgp, size_t, msgsz,
                long, msgtyp, int, msgflg)
{
        long err, mtype;

        err =  do_msgrcv(msqid, &mtype, msgp->mtext, msgsz, msgtyp, msgflg);
        if (err < 0)
                goto out;

        if (put_user(mtype, &msgp->mtype))
                err = -EFAULT;
out:
        return err;
}

#ifdef CONFIG_PROC_FS
static int sysvipc_msg_proc_show(struct seq_file *s, void *it)
{
        struct msg_queue *msq = it;

        return seq_printf(s,
                        "%10d %10d  %4o  %10lu %10lu %5u %5u %5u %5u %5u %5u %10lu %10lu %10lu\n",
                        msq->q_perm.key,
                        msq->q_perm.id,
                        msq->q_perm.mode,
                        msq->q_cbytes,
                        msq->q_qnum,
                        msq->q_lspid,
                        msq->q_lrpid,
                        msq->q_perm.uid,
                        msq->q_perm.gid,
                        msq->q_perm.cuid,
                        msq->q_perm.cgid,
                        msq->q_stime,
                        msq->q_rtime,
                        msq->q_ctime);
}
#endif