ipc: store ipcs into IDRs

This patch introduces ipcs storage into IDRs. The main changes are:
  . This ipc_ids structure is changed: the entries array is changed into a
    root idr structure.
  . The grow_ary() routine is removed: it is not needed anymore when adding
    an ipc structure, since we are now using the IDR facility.
  . The ipc_rmid() routine interface is changed:
       . there is no need for this routine to return the pointer passed in as
         argument: it is now declared as a void
       . since the id is now part of the kern_ipc_perm structure, no need to
         have it as an argument to the routine

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 330 insertions, 310 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index 319468609b76..08591a0278ce 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -75,13 +75,12 @@ static struct ipc_ids init_msg_ids;
 
 #define msg_lock(ns, id)        ((struct msg_queue*)ipc_lock(&msg_ids(ns), id))
 #define msg_unlock(msq)         ipc_unlock(&(msq)->q_perm)
-#define msg_rmid(ns, id)        ((struct msg_queue*)ipc_rmid(&msg_ids(ns), id))
 #define msg_checkid(ns, msq, msgid)     \
         ipc_checkid(&msg_ids(ns), &msq->q_perm, msgid)
 #define msg_buildid(ns, id, seq) \
         ipc_buildid(&msg_ids(ns), id, seq)
 
-static void freeque (struct ipc_namespace *ns, struct msg_queue *msq, int id);
+static void freeque(struct ipc_namespace *, struct msg_queue *);
 static int newque (struct ipc_namespace *ns, key_t key, int msgflg);
 #ifdef CONFIG_PROC_FS
 static int sysvipc_msg_proc_show(struct seq_file *s, void *it);
@@ -93,7 +92,7 @@ static void __msg_init_ns(struct ipc_namespace *ns, struct ipc_ids *ids)
         ns->msg_ctlmax = MSGMAX;
         ns->msg_ctlmnb = MSGMNB;
         ns->msg_ctlmni = MSGMNI;
-        ipc_init_ids(ids, ns->msg_ctlmni);
+        ipc_init_ids(ids);
 }
 
 int msg_init_ns(struct ipc_namespace *ns)
@@ -110,20 +109,24 @@ int msg_init_ns(struct ipc_namespace *ns)
 
 void msg_exit_ns(struct ipc_namespace *ns)
 {
-        int i;
         struct msg_queue *msq;
+        int next_id;
+        int total, in_use;
 
         mutex_lock(&msg_ids(ns).mutex);
-        for (i = 0; i <= msg_ids(ns).max_id; i++) {
-                msq = msg_lock(ns, i);
+
+        in_use = msg_ids(ns).in_use;
+
+        for (total = 0, next_id = 0; total < in_use; next_id++) {
+                msq = idr_find(&msg_ids(ns).ipcs_idr, next_id);
                 if (msq == NULL)
                         continue;
-
-                freeque(ns, msq, i);
+                ipc_lock_by_ptr(&msq->q_perm);
+                freeque(ns, msq);
+                total++;
         }
         mutex_unlock(&msg_ids(ns).mutex);
 
-        ipc_fini_ids(ns->ids[IPC_MSG_IDS]);
         kfree(ns->ids[IPC_MSG_IDS]);
         ns->ids[IPC_MSG_IDS] = NULL;
 }
@@ -136,6 +139,11 @@ void __init msg_init(void)
                                 IPC_MSG_IDS, sysvipc_msg_proc_show);
 }
 
+static inline void msg_rmid(struct ipc_namespace *ns, struct msg_queue *s)
+{
+        ipc_rmid(&msg_ids(ns), &s->q_perm);
+}
+
 static int newque (struct ipc_namespace *ns, key_t key, int msgflg)
 {
         struct msg_queue *msq;
@@ -155,6 +163,9 @@ static int newque (struct ipc_namespace *ns, key_t key, int msgflg)
                 return retval;
         }
 
+        /*
+         * ipc_addid() locks msq
+         */
         id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
         if (id == -1) {
                 security_msg_queue_free(msq);
@@ -162,7 +173,7 @@ static int newque (struct ipc_namespace *ns, key_t key, int msgflg)
                 return -ENOSPC;
         }
 
-        msq->q_id = msg_buildid(ns, id, msq->q_perm.seq);
+        msq->q_perm.id = msg_buildid(ns, id, msq->q_perm.seq);
         msq->q_stime = msq->q_rtime = 0;
         msq->q_ctime = get_seconds();
         msq->q_cbytes = msq->q_qnum = 0;
@@ -171,9 +182,10 @@ static int newque (struct ipc_namespace *ns, key_t key, int msgflg)
         INIT_LIST_HEAD(&msq->q_messages);
         INIT_LIST_HEAD(&msq->q_receivers);
         INIT_LIST_HEAD(&msq->q_senders);
+
         msg_unlock(msq);
 
-        return msq->q_id;
+        return msq->q_perm.id;
 }
 
 static inline void ss_add(struct msg_queue *msq, struct msg_sender *mss)
@@ -225,18 +237,18 @@ static void expunge_all(struct msg_queue *msq, int res)
 /*
  * freeque() wakes up waiters on the sender and receiver waiting queue,
  * removes the message queue from message queue ID
- * array, and cleans up all the messages associated with this queue.
+ * IDR, and cleans up all the messages associated with this queue.
  *
- * msg_ids.mutex and the spinlock for this message queue is hold
+ * msg_ids.mutex and the spinlock for this message queue are held
  * before freeque() is called. msg_ids.mutex remains locked on exit.
  */
-static void freeque(struct ipc_namespace *ns, struct msg_queue *msq, int id)
+static void freeque(struct ipc_namespace *ns, struct msg_queue *msq)
 {
         struct list_head *tmp;
 
         expunge_all(msq, -EIDRM);
         ss_wakeup(&msq->q_senders, 1);
-        msq = msg_rmid(ns, id);
+        msg_rmid(ns, msq);
         msg_unlock(msq);
 
         tmp = msq->q_messages.next;
@@ -255,36 +267,51 @@ static void freeque(struct ipc_namespace *ns, struct msg_queue *msq, int id)
 asmlinkage long sys_msgget(key_t key, int msgflg)
 {
         struct msg_queue *msq;
-        int id, ret = -EPERM;
+        int ret;
         struct ipc_namespace *ns;
 
         ns = current->nsproxy->ipc_ns;
-        
-        mutex_lock(&msg_ids(ns).mutex);
-        if (key == IPC_PRIVATE) 
-                ret = newque(ns, key, msgflg);
-        else if ((id = ipc_findkey(&msg_ids(ns), key)) == -1) { /* key not used */
-                if (!(msgflg & IPC_CREAT))
-                        ret = -ENOENT;
-                else
+
+        ret = idr_pre_get(&msg_ids(ns).ipcs_idr, GFP_KERNEL);
+
+        if (key == IPC_PRIVATE)  {
+                if (!ret)
+                        ret = -ENOMEM;
+                else {
+                        mutex_lock(&msg_ids(ns).mutex);
                         ret = newque(ns, key, msgflg);
-        } else if (msgflg & IPC_CREAT && msgflg & IPC_EXCL) {
-                ret = -EEXIST;
+                        mutex_unlock(&msg_ids(ns).mutex);
+                }
         } else {
-                msq = msg_lock(ns, id);
-                BUG_ON(msq == NULL);
-                if (ipcperms(&msq->q_perm, msgflg))
-                        ret = -EACCES;
-                else {
-                        int qid = msg_buildid(ns, id, msq->q_perm.seq);
-
-                        ret = security_msg_queue_associate(msq, msgflg);
-                        if (!ret)
-                                ret = qid;
+                mutex_lock(&msg_ids(ns).mutex);
+                msq = (struct msg_queue *) ipc_findkey(&msg_ids(ns), key);
+                if (msq == NULL) {
+                        /* key not used */
+                        if (!(msgflg & IPC_CREAT))
+                                ret = -ENOENT;
+                        else if (!ret)
+                                ret = -ENOMEM;
+                        else
+                                ret = newque(ns, key, msgflg);
+                } else {
+                        /* msq has been locked by ipc_findkey() */
+
+                        if (msgflg & IPC_CREAT && msgflg & IPC_EXCL)
+                                ret = -EEXIST;
+                        else {
+                                if (ipcperms(&msq->q_perm, msgflg))
+                                        ret = -EACCES;
+                                else {
+                                        ret = security_msg_queue_associate(
+                                                                msq, msgflg);
+                                        if (!ret)
+                                                ret = msq->q_perm.id;
+                                }
+                        }
+                        msg_unlock(msq);
                 }
-                msg_unlock(msq);
+                mutex_unlock(&msg_ids(ns).mutex);
         }
-        mutex_unlock(&msg_ids(ns).mutex);
 
         return ret;
 }
@@ -430,13 +457,13 @@ asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
                         msginfo.msgpool = MSGPOOL;
                         msginfo.msgtql = MSGTQL;
                 }
-                max_id = msg_ids(ns).max_id;
+                max_id = ipc_get_maxid(&msg_ids(ns));
                 mutex_unlock(&msg_ids(ns).mutex);
                 if (copy_to_user(buf, &msginfo, sizeof(struct msginfo)))
                         return -EFAULT;
                 return (max_id < 0) ? 0 : max_id;
         }
-        case MSG_STAT:
+        case MSG_STAT:  /* msqid is an index rather than a msg queue id */
         case IPC_STAT:
         {
                 struct msqid64_ds tbuf;
@@ -444,8 +471,6 @@ asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
 
                 if (!buf)
                         return -EFAULT;
-                if (cmd == MSG_STAT && msqid >= msg_ids(ns).entries->size)
-                        return -EINVAL;
 
                 memset(&tbuf, 0, sizeof(tbuf));
 
@@ -454,7 +479,7 @@ asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
                         return -EINVAL;
 
                 if (cmd == MSG_STAT) {
-                        success_return = msg_buildid(ns, msqid, msq->q_perm.seq);
+                        success_return = msq->q_perm.id;
                 } else {
                         err = -EIDRM;
                         if (msg_checkid(ns, msq, msqid))
@@ -552,7 +577,7 @@ asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
                 break;
         }
         case IPC_RMID:
-                freeque(ns, msq, msqid);
+                freeque(ns, msq);
                 break;
         }
         err = 0;
@@ -926,7 +951,7 @@ static int sysvipc_msg_proc_show(struct seq_file *s, void *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_id,
+                        msq->q_perm.id,
                         msq->q_perm.mode,
                         msq->q_cbytes,
                         msq->q_qnum,
diff --git a/ipc/sem.c b/ipc/sem.c
index 64ff4261f4e2..f92a2565d12b 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -90,7 +90,6 @@
 
 #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) \
@@ -99,7 +98,7 @@
 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);
+static void freeary(struct ipc_namespace *, struct sem_array *);
 #ifdef CONFIG_PROC_FS
 static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
 #endif
@@ -129,7 +128,7 @@ static void __sem_init_ns(struct ipc_namespace *ns, struct ipc_ids *ids)
         ns->sc_semopm = SEMOPM;
         ns->sc_semmni = SEMMNI;
         ns->used_sems = 0;
-        ipc_init_ids(ids, ns->sc_semmni);
+        ipc_init_ids(ids);
 }
 
 int sem_init_ns(struct ipc_namespace *ns)
@@ -146,20 +145,24 @@ int sem_init_ns(struct ipc_namespace *ns)
 
 void sem_exit_ns(struct ipc_namespace *ns)
 {
-        int i;
         struct sem_array *sma;
+        int next_id;
+        int total, in_use;
 
         mutex_lock(&sem_ids(ns).mutex);
-        for (i = 0; i <= sem_ids(ns).max_id; i++) {
-                sma = sem_lock(ns, i);
+
+        in_use = sem_ids(ns).in_use;
+
+        for (total = 0, next_id = 0; total < in_use; next_id++) {
+                sma = idr_find(&sem_ids(ns).ipcs_idr, next_id);
                 if (sma == NULL)
                         continue;
-
-                freeary(ns, sma, i);
+                ipc_lock_by_ptr(&sma->sem_perm);
+                freeary(ns, sma);
+                total++;
         }
         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;
 }
@@ -172,6 +175,11 @@ void __init sem_init (void)
                                 IPC_SEM_IDS, sysvipc_sem_proc_show);
 }
 
+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:
@@ -243,7 +251,7 @@ static int newary (struct ipc_namespace *ns, key_t key, int nsems, int semflg)
         }
         ns->used_sems += nsems;
 
-        sma->sem_id = sem_buildid(ns, id, sma->sem_perm.seq);
+        sma->sem_perm.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;
@@ -252,12 +260,12 @@ static int newary (struct ipc_namespace *ns, key_t key, int nsems, int semflg)
         sma->sem_ctime = get_seconds();
         sem_unlock(sma);
 
-        return sma->sem_id;
+        return sma->sem_perm.id;
 }
 
 asmlinkage long sys_semget (key_t key, int nsems, int semflg)
 {
-        int id, err = -EINVAL;
+        int err;
         struct sem_array *sma;
         struct ipc_namespace *ns;
 
@@ -265,34 +273,50 @@ asmlinkage long sys_semget (key_t key, int nsems, int semflg)
 
         if (nsems < 0 || nsems > ns->sc_semmsl)
                 return -EINVAL;
-        mutex_lock(&sem_ids(ns).mutex);
-        
+
+        err = idr_pre_get(&sem_ids(ns).ipcs_idr, GFP_KERNEL);
+
         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
+                if (!err)
+                        err = -ENOMEM;
+                else {
+                        mutex_lock(&sem_ids(ns).mutex);
                         err = newary(ns, key, nsems, semflg);
-        } else if (semflg & IPC_CREAT && semflg & IPC_EXCL) {
-                err = -EEXIST;
+                        mutex_unlock(&sem_ids(ns).mutex);
+                }
         } 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;
+                mutex_lock(&sem_ids(ns).mutex);
+                sma = (struct sem_array *) ipc_findkey(&sem_ids(ns), key);
+                if (sma == NULL) {
+                        /* key not used */
+                        if (!(semflg & IPC_CREAT))
+                                err = -ENOENT;
+                        else if (!err)
+                                err = -ENOMEM;
+                        else
+                                err = newary(ns, key, nsems, semflg);
+                } else {
+                        /* sma has been locked by ipc_findkey() */
+
+                        if (semflg & IPC_CREAT && semflg & IPC_EXCL)
+                                err = -EEXIST;
+                        else {
+                                if (nsems > sma->sem_nsems)
+                                        err = -EINVAL;
+                                else if (ipcperms(&sma->sem_perm, semflg))
+                                        err = -EACCES;
+                                else {
+                                        err = security_sem_associate(sma,
+                                                                semflg);
+                                        if (!err)
+                                                err = sma->sem_perm.id;
+                                }
+                        }
+                        sem_unlock(sma);
                 }
-                sem_unlock(sma);
+                mutex_unlock(&sem_ids(ns).mutex);
         }
 
-        mutex_unlock(&sem_ids(ns).mutex);
         return err;
 }
 
@@ -491,11 +515,10 @@ static int count_semzcnt (struct sem_array * sma, ushort semnum)
  * 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)
+static void freeary(struct ipc_namespace *ns, struct sem_array *sma)
 {
         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()
@@ -518,12 +541,11 @@ static void freeary (struct ipc_namespace *ns, struct sem_array *sma, int id)
                 q = n;
         }
 
-        /* Remove the semaphore set from the ID array*/
-        sma = sem_rmid(ns, id);
+        /* Remove the semaphore set from the IDR */
+        sem_rmid(ns, sma);
         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);
 }
@@ -584,7 +606,7 @@ static int semctl_nolock(struct ipc_namespace *ns, int semid, int semnum,
                         seminfo.semusz = SEMUSZ;
                         seminfo.semaem = SEMAEM;
                 }
-                max_id = sem_ids(ns).max_id;
+                max_id = ipc_get_maxid(&sem_ids(ns));
                 mutex_unlock(&sem_ids(ns).mutex);
                 if (copy_to_user (arg.__buf, &seminfo, sizeof(struct seminfo))) 
                         return -EFAULT;
@@ -595,9 +617,6 @@ static int semctl_nolock(struct ipc_namespace *ns, int semid, int semnum,
                 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);
@@ -612,7 +631,7 @@ static int semctl_nolock(struct ipc_namespace *ns, int semid, int semnum,
                 if (err)
                         goto out_unlock;
 
-                id = sem_buildid(ns, semid, sma->sem_perm.seq);
+                id = sma->sem_perm.id;
 
                 kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
                 tbuf.sem_otime  = sma->sem_otime;
@@ -894,7 +913,7 @@ static int semctl_down(struct ipc_namespace *ns, int semid, int semnum,
 
         switch(cmd){
         case IPC_RMID:
-                freeary(ns, sma, semid);
+                freeary(ns, sma);
                 err = 0;
                 break;
         case IPC_SET:
@@ -1402,7 +1421,7 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *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.id,
                           sma->sem_perm.mode,
                           sma->sem_nsems,
                           sma->sem_perm.uid,
diff --git a/ipc/shm.c b/ipc/shm.c
index b9d272900a1e..dcc333239683 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -84,7 +84,7 @@ static void __shm_init_ns(struct ipc_namespace *ns, struct ipc_ids *ids)
         ns->shm_ctlall = SHMALL;
         ns->shm_ctlmni = SHMMNI;
         ns->shm_tot = 0;
-        ipc_init_ids(ids, 1);
+        ipc_init_ids(ids);
 }
 
 static void do_shm_rmid(struct ipc_namespace *ns, struct shmid_kernel *shp)
@@ -112,20 +112,24 @@ int shm_init_ns(struct ipc_namespace *ns)
 
 void shm_exit_ns(struct ipc_namespace *ns)
 {
-        int i;
         struct shmid_kernel *shp;
+        int next_id;
+        int total, in_use;
 
         mutex_lock(&shm_ids(ns).mutex);
-        for (i = 0; i <= shm_ids(ns).max_id; i++) {
-                shp = shm_lock(ns, i);
+
+        in_use = shm_ids(ns).in_use;
+
+        for (total = 0, next_id = 0; total < in_use; next_id++) {
+                shp = idr_find(&shm_ids(ns).ipcs_idr, next_id);
                 if (shp == NULL)
                         continue;
-
+                ipc_lock_by_ptr(&shp->shm_perm);
                 do_shm_rmid(ns, shp);
+                total++;
         }
         mutex_unlock(&shm_ids(ns).mutex);
 
-        ipc_fini_ids(ns->ids[IPC_SHM_IDS]);
         kfree(ns->ids[IPC_SHM_IDS]);
         ns->ids[IPC_SHM_IDS] = NULL;
 }
@@ -146,9 +150,9 @@ static inline int shm_checkid(struct ipc_namespace *ns,
         return 0;
 }
 
-static inline struct shmid_kernel *shm_rmid(struct ipc_namespace *ns, int id)
+static inline void shm_rmid(struct ipc_namespace *ns, struct shmid_kernel *s)
 {
-        return (struct shmid_kernel *)ipc_rmid(&shm_ids(ns), id);
+        ipc_rmid(&shm_ids(ns), &s->shm_perm);
 }
 
 static inline int shm_addid(struct ipc_namespace *ns, struct shmid_kernel *shp)
@@ -184,7 +188,7 @@ static void shm_open(struct vm_area_struct *vma)
 static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
 {
         ns->shm_tot -= (shp->shm_segsz + PAGE_SIZE - 1) >> PAGE_SHIFT;
-        shm_rmid(ns, shp->id);
+        shm_rmid(ns, shp);
         shm_unlock(shp);
         if (!is_file_hugepages(shp->shm_file))
                 shmem_lock(shp->shm_file, 0, shp->mlock_user);
@@ -398,17 +402,18 @@ static int newseg (struct ipc_namespace *ns, key_t key, int shmflg, size_t size)
         shp->shm_ctim = get_seconds();
         shp->shm_segsz = size;
         shp->shm_nattch = 0;
-        shp->id = shm_buildid(ns, id, shp->shm_perm.seq);
+        shp->shm_perm.id = shm_buildid(ns, id, shp->shm_perm.seq);
         shp->shm_file = file;
         /*
          * shmid gets reported as "inode#" in /proc/pid/maps.
          * proc-ps tools use this. Changing this will break them.
          */
-        file->f_dentry->d_inode->i_ino = shp->id;
+        file->f_dentry->d_inode->i_ino = shp->shm_perm.id;
 
         ns->shm_tot += numpages;
+        error = shp->shm_perm.id;
         shm_unlock(shp);
-        return shp->id;
+        return error;
 
 no_id:
         fput(file);
@@ -421,37 +426,52 @@ no_file:
 asmlinkage long sys_shmget (key_t key, size_t size, int shmflg)
 {
         struct shmid_kernel *shp;
-        int err, id = 0;
+        int err;
         struct ipc_namespace *ns;
 
         ns = current->nsproxy->ipc_ns;
 
-        mutex_lock(&shm_ids(ns).mutex);
+        err = idr_pre_get(&shm_ids(ns).ipcs_idr, GFP_KERNEL);
+
         if (key == IPC_PRIVATE) {
-                err = newseg(ns, key, shmflg, size);
-        } else if ((id = ipc_findkey(&shm_ids(ns), key)) == -1) {
-                if (!(shmflg & IPC_CREAT))
-                        err = -ENOENT;
-                else
+                if (!err)
+                        err = -ENOMEM;
+                else {
+                        mutex_lock(&shm_ids(ns).mutex);
                         err = newseg(ns, key, shmflg, size);
-        } else if ((shmflg & IPC_CREAT) && (shmflg & IPC_EXCL)) {
-                err = -EEXIST;
+                        mutex_unlock(&shm_ids(ns).mutex);
+                }
         } else {
-                shp = shm_lock(ns, id);
-                BUG_ON(shp==NULL);
-                if (shp->shm_segsz < size)
-                        err = -EINVAL;
-                else if (ipcperms(&shp->shm_perm, shmflg))
-                        err = -EACCES;
-                else {
-                        int shmid = shm_buildid(ns, id, shp->shm_perm.seq);
-                        err = security_shm_associate(shp, shmflg);
-                        if (!err)
-                                err = shmid;
+                mutex_lock(&shm_ids(ns).mutex);
+                shp = (struct shmid_kernel *) ipc_findkey(&shm_ids(ns), key);
+                if (shp == NULL) {
+                        if (!(shmflg & IPC_CREAT))
+                                err = -ENOENT;
+                        else if (!err)
+                                err = -ENOMEM;
+                        else
+                                err = newseg(ns, key, shmflg, size);
+                } else {
+                        /* shp has been locked by ipc_findkey() */
+
+                        if ((shmflg & IPC_CREAT) && (shmflg & IPC_EXCL))
+                                err = -EEXIST;
+                        else {
+                                if (shp->shm_segsz < size)
+                                        err = -EINVAL;
+                                else if (ipcperms(&shp->shm_perm, shmflg))
+                                        err = -EACCES;
+                                else {
+                                        err = security_shm_associate(shp,
+                                                                shmflg);
+                                        if (!err)
+                                                err = shp->shm_perm.id;
+                                }
+                        }
+                        shm_unlock(shp);
                 }
-                shm_unlock(shp);
+                mutex_unlock(&shm_ids(ns).mutex);
         }
-        mutex_unlock(&shm_ids(ns).mutex);
 
         return err;
 }
@@ -550,17 +570,20 @@ static inline unsigned long copy_shminfo_to_user(void __user *buf, struct shminf
 static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
                 unsigned long *swp)
 {
-        int i;
+        int next_id;
+        int total, in_use;
 
         *rss = 0;
         *swp = 0;
 
-        for (i = 0; i <= shm_ids(ns).max_id; i++) {
+        in_use = shm_ids(ns).in_use;
+
+        for (total = 0, next_id = 0; total < in_use; next_id++) {
                 struct shmid_kernel *shp;
                 struct inode *inode;
 
-                shp = shm_get(ns, i);
-                if(!shp)
+                shp = shm_get(ns, next_id);
+                if (shp == NULL)
                         continue;
 
                 inode = shp->shm_file->f_path.dentry->d_inode;
@@ -575,6 +598,8 @@ static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
                         *swp += info->swapped;
                         spin_unlock(&info->lock);
                 }
+
+                total++;
         }
 }
 
@@ -611,7 +636,7 @@ asmlinkage long sys_shmctl (int shmid, int cmd, struct shmid_ds __user *buf)
                 if(copy_shminfo_to_user (buf, &shminfo, version))
                         return -EFAULT;
                 /* reading a integer is always atomic */
-                err= shm_ids(ns).max_id;
+                err = ipc_get_maxid(&shm_ids(ns));
                 if(err<0)
                         err = 0;
                 goto out;
@@ -631,7 +656,7 @@ asmlinkage long sys_shmctl (int shmid, int cmd, struct shmid_ds __user *buf)
                 shm_info.shm_tot = ns->shm_tot;
                 shm_info.swap_attempts = 0;
                 shm_info.swap_successes = 0;
-                err = shm_ids(ns).max_id;
+                err = ipc_get_maxid(&shm_ids(ns));
                 mutex_unlock(&shm_ids(ns).mutex);
                 if(copy_to_user (buf, &shm_info, sizeof(shm_info))) {
                         err = -EFAULT;
@@ -651,11 +676,8 @@ asmlinkage long sys_shmctl (int shmid, int cmd, struct shmid_ds __user *buf)
                 if(shp==NULL) {
                         err = -EINVAL;
                         goto out;
-                } else if(cmd==SHM_STAT) {
-                        err = -EINVAL;
-                        if (shmid > shm_ids(ns).max_id)
-                                goto out_unlock;
-                        result = shm_buildid(ns, shmid, shp->shm_perm.seq);
+                } else if (cmd == SHM_STAT) {
+                        result = shp->shm_perm.id;
                 } else {
                         err = shm_checkid(ns, shp,shmid);
                         if(err)
@@ -925,7 +947,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
 
         file->private_data = sfd;
         file->f_mapping = shp->shm_file->f_mapping;
-        sfd->id = shp->id;
+        sfd->id = shp->shm_perm.id;
         sfd->ns = get_ipc_ns(ns);
         sfd->file = shp->shm_file;
         sfd->vm_ops = NULL;
@@ -1094,7 +1116,7 @@ static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
                 format = BIG_STRING;
         return seq_printf(s, format,
                           shp->shm_perm.key,
-                          shp->id,
+                          shp->shm_perm.id,
                           shp->shm_perm.mode,
                           shp->shm_segsz,
                           shp->shm_cprid,
diff --git a/ipc/util.c b/ipc/util.c
index 44e5135aee47..2a205875d277 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -129,23 +129,16 @@ __initcall(ipc_init);
 /**
  *      ipc_init_ids            -       initialise IPC identifiers
  *      @ids: Identifier set
- *      @size: Number of identifiers
  *
- *      Given a size for the ipc identifier range (limited below IPCMNI)
- *      set up the sequence range to use then allocate and initialise the
- *      array itself. 
+ *      Set up the sequence range to use for the ipc identifier range (limited
+ *      below IPCMNI) then initialise the ids idr.
  */
  
-void ipc_init_ids(struct ipc_ids* ids, int size)
+void ipc_init_ids(struct ipc_ids *ids)
 {
-        int i;
-
         mutex_init(&ids->mutex);
 
-        if(size > IPCMNI)
-                size = IPCMNI;
         ids->in_use = 0;
-        ids->max_id = -1;
         ids->seq = 0;
         {
                 int seq_limit = INT_MAX/SEQ_MULTIPLIER;
@@ -155,17 +148,7 @@ void ipc_init_ids(struct ipc_ids* ids, int size)
                         ids->seq_max = seq_limit;
         }
 
-        ids->entries = ipc_rcu_alloc(sizeof(struct kern_ipc_perm *)*size +
-                                     sizeof(struct ipc_id_ary));
-
-        if(ids->entries == NULL) {
-                printk(KERN_ERR "ipc_init_ids() failed, ipc service disabled.\n");
-                size = 0;
-                ids->entries = &ids->nullentry;
-        }
-        ids->entries->size = size;
-        for(i=0;i<size;i++)
-                ids->entries->p[i] = NULL;
+        idr_init(&ids->ipcs_idr);
 }
 
 #ifdef CONFIG_PROC_FS
@@ -209,72 +192,73 @@ void __init ipc_init_proc_interface(const char *path, const char *header,
  *      @key: The key to find
  *      
  *      Requires ipc_ids.mutex locked.
- *      Returns the identifier if found or -1 if not.
+ *      Returns the LOCKED pointer to the ipc structure if found or NULL
+ *      if not.
+ *      If key is found ipc contains its ipc structure
  */
  
-int ipc_findkey(struct ipc_ids* ids, key_t key)
+struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
 {
-        int id;
-        struct kern_ipc_perm* p;
-        int max_id = ids->max_id;
+        struct kern_ipc_perm *ipc;
+        int next_id;
+        int total;
 
-        /*
-         * rcu_dereference() is not needed here
-         * since ipc_ids.mutex is held
-         */
-        for (id = 0; id <= max_id; id++) {
-                p = ids->entries->p[id];
-                if(p==NULL)
+        for (total = 0, next_id = 0; total < ids->in_use; next_id++) {
+                ipc = idr_find(&ids->ipcs_idr, next_id);
+
+                if (ipc == NULL)
                         continue;
-                if (key == p->key)
-                        return id;
+
+                if (ipc->key != key) {
+                        total++;
+                        continue;
+                }
+
+                ipc_lock_by_ptr(ipc);
+                return ipc;
         }
-        return -1;
+
+        return NULL;
 }
 
-/*
- * Requires ipc_ids.mutex locked
+/**
+ *      ipc_get_maxid   -       get the last assigned id
+ *      @ids: IPC identifier set
+ *
+ *      Called with ipc_ids.mutex held.
  */
-static int grow_ary(struct ipc_ids* ids, int newsize)
-{
-        struct ipc_id_ary* new;
-        struct ipc_id_ary* old;
-        int i;
-        int size = ids->entries->size;
-
-        if(newsize > IPCMNI)
-                newsize = IPCMNI;
-        if(newsize <= size)
-                return newsize;
-
-        new = ipc_rcu_alloc(sizeof(struct kern_ipc_perm *)*newsize +
-                            sizeof(struct ipc_id_ary));
-        if(new == NULL)
-                return size;
-        new->size = newsize;
-        memcpy(new->p, ids->entries->p, sizeof(struct kern_ipc_perm *)*size);
-        for(i=size;i<newsize;i++) {
-                new->p[i] = NULL;
-        }
-        old = ids->entries;
 
-        /*
-         * Use rcu_assign_pointer() to make sure the memcpyed contents
-         * of the new array are visible before the new array becomes visible.
-         */
-        rcu_assign_pointer(ids->entries, new);
+int ipc_get_maxid(struct ipc_ids *ids)
+{
+        struct kern_ipc_perm *ipc;
+        int max_id = -1;
+        int total, id;
+
+        if (ids->in_use == 0)
+                return -1;
 
-        __ipc_fini_ids(ids, old);
-        return newsize;
+        if (ids->in_use == IPCMNI)
+                return IPCMNI - 1;
+
+        /* Look for the last assigned id */
+        total = 0;
+        for (id = 0; id < IPCMNI && total < ids->in_use; id++) {
+                ipc = idr_find(&ids->ipcs_idr, id);
+                if (ipc != NULL) {
+                        max_id = id;
+                        total++;
+                }
+        }
+        return max_id;
 }
 
 /**
  *      ipc_addid       -       add an IPC identifier
  *      @ids: IPC identifier set
  *      @new: new IPC permission set
- *      @size: new size limit for the id array
+ *      @size: limit for the number of used ids
  *
- *      Add an entry 'new' to the IPC arrays. The permissions object is
+ *      Add an entry 'new' to the IPC idr. The permissions object is
  *      initialised and the first free entry is set up and the id assigned
  *      is returned. The list is returned in a locked state on success.
  *      On failure the list is not locked and -1 is returned.
@@ -284,23 +268,23 @@ static int grow_ary(struct ipc_ids* ids, int newsize)
  
 int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
 {
-        int id;
-
-        size = grow_ary(ids,size);
+        int id, err;
 
         /*
          * rcu_dereference()() is not needed here since
          * ipc_ids.mutex is held
          */
-        for (id = 0; id < size; id++) {
-                if(ids->entries->p[id] == NULL)
-                        goto found;
-        }
-        return -1;
-found:
+        if (size > IPCMNI)
+                size = IPCMNI;
+
+        if (ids->in_use >= size)
+                return -1;
+
+        err = idr_get_new(&ids->ipcs_idr, new, &id);
+        if (err)
+                return -1;
+
         ids->in_use++;
-        if (id > ids->max_id)
-                ids->max_id = id;
 
         new->cuid = new->uid = current->euid;
         new->gid = new->cgid = current->egid;
@@ -313,48 +297,32 @@ found:
         new->deleted = 0;
         rcu_read_lock();
         spin_lock(&new->lock);
-        ids->entries->p[id] = new;
         return id;
 }
 
 /**
  *      ipc_rmid        -       remove an IPC identifier
  *      @ids: identifier set
- *      @id: Identifier to remove
+ *      @id: ipc perm structure containing the identifier to remove
  *
  *      The identifier must be valid, and in use. The kernel will panic if
  *      fed an invalid identifier. The entry is removed and internal
- *      variables recomputed. The object associated with the identifier
- *      is returned.
- *      ipc_ids.mutex and the spinlock for this ID is hold before this function
- *      is called, and remain locked on the exit.
+ *      variables recomputed.
+ *      ipc_ids.mutex and the spinlock for this ID are held before this
+ *      function is called, and remain locked on the exit.
  */
  
-struct kern_ipc_perm* ipc_rmid(struct ipc_ids* ids, int id)
+void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
 {
-        struct kern_ipc_perm* p;
-        int lid = id % SEQ_MULTIPLIER;
-        BUG_ON(lid >= ids->entries->size);
+        int lid = ipcp->id % SEQ_MULTIPLIER;
+
+        idr_remove(&ids->ipcs_idr, lid);
 
-        /* 
-         * do not need a rcu_dereference()() here to force ordering
-         * on Alpha, since the ipc_ids.mutex is held.
-         */     
-        p = ids->entries->p[lid];
-        ids->entries->p[lid] = NULL;
-        BUG_ON(p==NULL);
         ids->in_use--;
 
-        if (lid == ids->max_id) {
-                do {
-                        lid--;
-                        if(lid == -1)
-                                break;
-                } while (ids->entries->p[lid] == NULL);
-                ids->max_id = lid;
-        }
-        p->deleted = 1;
-        return p;
+        ipcp->deleted = 1;
+
+        return;
 }
 
 /**
@@ -613,33 +581,26 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out)
  * if in the future ipc_get() is used by other places without ipc_ids.mutex
  * down, then ipc_get() needs read memery barriers as ipc_lock() does.
  */
-struct kern_ipc_perm* ipc_get(struct ipc_ids* ids, int id)
+struct kern_ipc_perm *ipc_get(struct ipc_ids *ids, int id)
 {
-        struct kern_ipc_perm* out;
+        struct kern_ipc_perm *out;
         int lid = id % SEQ_MULTIPLIER;
-        if(lid >= ids->entries->size)
-                return NULL;
-        out = ids->entries->p[lid];
+        out = idr_find(&ids->ipcs_idr, lid);
         return out;
 }
 
-struct kern_ipc_perm* ipc_lock(struct ipc_ids* ids, int id)
+struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
 {
-        struct kern_ipc_perm* out;
+        struct kern_ipc_perm *out;
         int lid = id % SEQ_MULTIPLIER;
-        struct ipc_id_ary* entries;
 
         rcu_read_lock();
-        entries = rcu_dereference(ids->entries);
-        if(lid >= entries->size) {
-                rcu_read_unlock();
-                return NULL;
-        }
-        out = entries->p[lid];
-        if(out == NULL) {
+        out = idr_find(&ids->ipcs_idr, lid);
+        if (out == NULL) {
                 rcu_read_unlock();
                 return NULL;
         }
+
         spin_lock(&out->lock);
         
         /* ipc_rmid() may have already freed the ID while ipc_lock
@@ -650,6 +611,7 @@ struct kern_ipc_perm* ipc_lock(struct ipc_ids* ids, int id)
                 rcu_read_unlock();
                 return NULL;
         }
+
         return out;
 }
 
@@ -707,27 +669,30 @@ struct ipc_proc_iter {
         struct ipc_proc_iface *iface;
 };
 
-static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
+/*
+ * This routine locks the ipc structure found at least at position pos.
+ */
+struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t pos,
+                                        loff_t *new_pos)
 {
-        struct ipc_proc_iter *iter = s->private;
-        struct ipc_proc_iface *iface = iter->iface;
-        struct kern_ipc_perm *ipc = it;
-        loff_t p;
-        struct ipc_ids *ids;
+        struct kern_ipc_perm *ipc;
+        int total, id;
 
-        ids = iter->ns->ids[iface->ids];
+        total = 0;
+        for (id = 0; id < pos && total < ids->in_use; id++) {
+                ipc = idr_find(&ids->ipcs_idr, id);
+                if (ipc != NULL)
+                        total++;
+        }
 
-        /* If we had an ipc id locked before, unlock it */
-        if (ipc && ipc != SEQ_START_TOKEN)
-                ipc_unlock(ipc);
+        if (total >= ids->in_use)
+                return NULL;
 
-        /*
-         * p = *pos - 1 (because id 0 starts at position 1)
-         *          + 1 (because we increment the position by one)
-         */
-        for (p = *pos; p <= ids->max_id; p++) {
-                if ((ipc = ipc_lock(ids, p)) != NULL) {
-                        *pos = p + 1;
+        for ( ; pos < IPCMNI; pos++) {
+                ipc = idr_find(&ids->ipcs_idr, pos);
+                if (ipc != NULL) {
+                        *new_pos = pos + 1;
+                        ipc_lock_by_ptr(ipc);
                         return ipc;
                 }
         }
@@ -736,6 +701,19 @@ static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
         return NULL;
 }
 
+static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
+{
+        struct ipc_proc_iter *iter = s->private;
+        struct ipc_proc_iface *iface = iter->iface;
+        struct kern_ipc_perm *ipc = it;
+
+        /* If we had an ipc id locked before, unlock it */
+        if (ipc && ipc != SEQ_START_TOKEN)
+                ipc_unlock(ipc);
+
+        return sysvipc_find_ipc(iter->ns->ids[iface->ids], *pos, pos);
+}
+
 /*
  * File positions: pos 0 -> header, pos n -> ipc id + 1.
  * SeqFile iterator: iterator value locked shp or SEQ_TOKEN_START.
@@ -744,8 +722,6 @@ static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
 {
         struct ipc_proc_iter *iter = s->private;
         struct ipc_proc_iface *iface = iter->iface;
-        struct kern_ipc_perm *ipc;
-        loff_t p;
         struct ipc_ids *ids;
 
         ids = iter->ns->ids[iface->ids];
@@ -765,13 +741,7 @@ static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
                 return SEQ_START_TOKEN;
 
         /* Find the (pos-1)th ipc */
-        for (p = *pos - 1; p <= ids->max_id; p++) {
-                if ((ipc = ipc_lock(ids, p)) != NULL) {
-                        *pos = p + 1;
-                        return ipc;
-                }
-        }
-        return NULL;
+        return sysvipc_find_ipc(ids, *pos - 1, pos);
 }
 
 static void sysvipc_proc_stop(struct seq_file *s, void *it)
diff --git a/ipc/util.h b/ipc/util.h
index 333e891bcaca..c9063267d4f8 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -10,6 +10,8 @@
 #ifndef _IPC_UTIL_H
 #define _IPC_UTIL_H
 
+#include <linux/idr.h>
+
 #define USHRT_MAX 0xffff
 #define SEQ_MULTIPLIER  (IPCMNI)
 
@@ -25,24 +27,17 @@ void sem_exit_ns(struct ipc_namespace *ns);
 void msg_exit_ns(struct ipc_namespace *ns);
 void shm_exit_ns(struct ipc_namespace *ns);
 
-struct ipc_id_ary {
-        int size;
-        struct kern_ipc_perm *p[0];
-};
-
 struct ipc_ids {
         int in_use;
-        int max_id;
         unsigned short seq;
         unsigned short seq_max;
         struct mutex mutex;
-        struct ipc_id_ary nullentry;
-        struct ipc_id_ary* entries;
+        struct idr ipcs_idr;
 };
 
 struct seq_file;
 
-void ipc_init_ids(struct ipc_ids *ids, int size);
+void ipc_init_ids(struct ipc_ids *);
 #ifdef CONFIG_PROC_FS
 void __init ipc_init_proc_interface(const char *path, const char *header,
                 int ids, int (*show)(struct seq_file *, void *));
@@ -55,11 +50,12 @@ void __init ipc_init_proc_interface(const char *path, const char *header,
 #define IPC_SHM_IDS     2
 
 /* must be called with ids->mutex acquired.*/
-int ipc_findkey(struct ipc_ids* ids, key_t key);
-int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size);
+struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key);
+int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int);
+int ipc_get_maxid(struct ipc_ids *);
 
 /* must be called with both locks acquired. */
-struct kern_ipc_perm* ipc_rmid(struct ipc_ids* ids, int id);
+void ipc_rmid(struct ipc_ids *, struct kern_ipc_perm *);
 
 int ipcperms (struct kern_ipc_perm *ipcp, short flg);
 
@@ -79,18 +75,6 @@ void* ipc_rcu_alloc(int size);
 void ipc_rcu_getref(void *ptr);
 void ipc_rcu_putref(void *ptr);
 
-static inline void __ipc_fini_ids(struct ipc_ids *ids,
-                struct ipc_id_ary *entries)
-{
-        if (entries != &ids->nullentry)
-                ipc_rcu_putref(entries);
-}
-
-static inline void ipc_fini_ids(struct ipc_ids *ids)
-{
-        __ipc_fini_ids(ids, ids->entries);
-}
-
 struct kern_ipc_perm* ipc_get(struct ipc_ids* ids, int id);
 struct kern_ipc_perm* ipc_lock(struct ipc_ids* ids, int id);
 void ipc_lock_by_ptr(struct kern_ipc_perm *ipcp);