ipc: merge ipc_rcu and kern_ipc_perm

ipc has two management structures that exist for every id:
 - struct kern_ipc_perm, it contains e.g. the permissions.
 - struct ipc_rcu, it contains the rcu head for rcu handling and the
   refcount.

The patch merges both structures.

As a bonus, we may save one cacheline, because both structures are
cacheline aligned.  In addition, it reduces the number of casts, instead
most codepaths can use container_of.

To simplify code, the ipc_rcu_alloc initializes the allocation to 0.

[manfred@colorfullife.com: really include the memset() into ipc_alloc_rcu()]
Link: http://lkml.kernel.org/r/564f8612-0601-b267-514f-a9f650ec9b32@colorfullife.com
Link: http://lkml.kernel.org/r/20170525185107.12869-3-manfred@colorfullife.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/ipc.h b/include/linux/ipc.h
index 71fd92d..5591f05 100644 (file)
--- a/include/linux/ipc.h
+++ b/include/linux/ipc.h
@@ -20,6 +20,9 @@ struct kern_ipc_perm {
        umode_t         mode;
        unsigned long   seq;
        void            *security;
+
+       struct rcu_head rcu;
+       atomic_t refcount;
 } ____cacheline_aligned_in_smp;
 
 #endif /* _LINUX_IPC_H */

diff --git a/ipc/msg.c b/ipc/msg.c
index 104926d..0ed7dae 100644 (file)
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -97,8 +97,8 @@ static inline void msg_rmid(struct ipc_namespace *ns, struct msg_queue *s)
 
 static void msg_rcu_free(struct rcu_head *head)
 {
-       struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
-       struct msg_queue *msq = ipc_rcu_to_struct(p);
+       struct kern_ipc_perm *p = container_of(head, struct kern_ipc_perm, rcu);
+       struct msg_queue *msq = container_of(p, struct msg_queue, q_perm);
 
        security_msg_queue_free(msq);
        ipc_rcu_free(head);
@@ -118,7 +118,10 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
        key_t key = params->key;
        int msgflg = params->flg;
 
-       msq = ipc_rcu_alloc(sizeof(*msq));
+       BUILD_BUG_ON(offsetof(struct msg_queue, q_perm) != 0);
+
+       msq = container_of(ipc_rcu_alloc(sizeof(*msq)), struct msg_queue,
+                               q_perm);
        if (!msq)
                return -ENOMEM;
 
@@ -128,7 +131,7 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
        msq->q_perm.security = NULL;
        retval = security_msg_queue_alloc(msq);
        if (retval) {
-               ipc_rcu_putref(msq, ipc_rcu_free);
+               ipc_rcu_putref(&msq->q_perm, ipc_rcu_free);
                return retval;
        }
 
@@ -144,7 +147,7 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
        /* ipc_addid() locks msq upon success. */
        id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
        if (id < 0) {
-               ipc_rcu_putref(msq, msg_rcu_free);
+               ipc_rcu_putref(&msq->q_perm, msg_rcu_free);
                return id;
        }
 
@@ -249,7 +252,7 @@ static void freeque(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
                free_msg(msg);
        }
        atomic_sub(msq->q_cbytes, &ns->msg_bytes);
-       ipc_rcu_putref(msq, msg_rcu_free);
+       ipc_rcu_putref(&msq->q_perm, msg_rcu_free);
 }
 
 /*
@@ -688,7 +691,7 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
                /* enqueue the sender and prepare to block */
                ss_add(msq, &s, msgsz);
 
-               if (!ipc_rcu_getref(msq)) {
+               if (!ipc_rcu_getref(&msq->q_perm)) {
                        err = -EIDRM;
                        goto out_unlock0;
                }
@@ -700,7 +703,7 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
                rcu_read_lock();
                ipc_lock_object(&msq->q_perm);
 
-               ipc_rcu_putref(msq, msg_rcu_free);
+               ipc_rcu_putref(&msq->q_perm, msg_rcu_free);
                /* raced with RMID? */
                if (!ipc_valid_object(&msq->q_perm)) {
                        err = -EIDRM;

diff --git a/ipc/sem.c b/ipc/sem.c
index fff8337..bdff6d9 100644 (file)
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -260,8 +260,8 @@ static void merge_queues(struct sem_array *sma)
 
 static void sem_rcu_free(struct rcu_head *head)
 {
-       struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
-       struct sem_array *sma = ipc_rcu_to_struct(p);
+       struct kern_ipc_perm *p = container_of(head, struct kern_ipc_perm, rcu);
+       struct sem_array *sma = container_of(p, struct sem_array, sem_perm);
 
        security_sem_free(sma);
        ipc_rcu_free(head);
@@ -438,7 +438,7 @@ static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns
 static inline void sem_lock_and_putref(struct sem_array *sma)
 {
        sem_lock(sma, NULL, -1);
-       ipc_rcu_putref(sma, sem_rcu_free);
+       ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
 }
 
 static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
@@ -469,20 +469,20 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
        if (ns->used_sems + nsems > ns->sc_semmns)
                return -ENOSPC;
 
+       BUILD_BUG_ON(offsetof(struct sem_array, sem_perm) != 0);
+
        size = sizeof(*sma) + nsems * sizeof(sma->sems[0]);
-       sma = ipc_rcu_alloc(size);
+       sma = container_of(ipc_rcu_alloc(size), struct sem_array, sem_perm);
        if (!sma)
                return -ENOMEM;
 
-       memset(sma, 0, size);
-
        sma->sem_perm.mode = (semflg & S_IRWXUGO);
        sma->sem_perm.key = key;
 
        sma->sem_perm.security = NULL;
        retval = security_sem_alloc(sma);
        if (retval) {
-               ipc_rcu_putref(sma, ipc_rcu_free);
+               ipc_rcu_putref(&sma->sem_perm, ipc_rcu_free);
                return retval;
        }
 
@@ -502,7 +502,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 
        id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
        if (id < 0) {
-               ipc_rcu_putref(sma, sem_rcu_free);
+               ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
                return id;
        }
        ns->used_sems += nsems;
@@ -1122,7 +1122,7 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
 
        wake_up_q(&wake_q);
        ns->used_sems -= sma->sem_nsems;
-       ipc_rcu_putref(sma, sem_rcu_free);
+       ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
 }
 
 static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version)
@@ -1362,7 +1362,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
                        goto out_unlock;
                }
                if (nsems > SEMMSL_FAST) {
-                       if (!ipc_rcu_getref(sma)) {
+                       if (!ipc_rcu_getref(&sma->sem_perm)) {
                                err = -EIDRM;
                                goto out_unlock;
                        }
@@ -1370,7 +1370,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
                        rcu_read_unlock();
                        sem_io = ipc_alloc(sizeof(ushort)*nsems);
                        if (sem_io == NULL) {
-                               ipc_rcu_putref(sma, sem_rcu_free);
+                               ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
                                return -ENOMEM;
                        }
 
@@ -1395,7 +1395,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
                int i;
                struct sem_undo *un;
 
-               if (!ipc_rcu_getref(sma)) {
+               if (!ipc_rcu_getref(&sma->sem_perm)) {
                        err = -EIDRM;
                        goto out_rcu_wakeup;
                }
@@ -1404,20 +1404,20 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
                if (nsems > SEMMSL_FAST) {
                        sem_io = ipc_alloc(sizeof(ushort)*nsems);
                        if (sem_io == NULL) {
-                               ipc_rcu_putref(sma, sem_rcu_free);
+                               ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
                                return -ENOMEM;
                        }
                }
 
                if (copy_from_user(sem_io, p, nsems*sizeof(ushort))) {
-                       ipc_rcu_putref(sma, sem_rcu_free);
+                       ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
                        err = -EFAULT;
                        goto out_free;
                }
 
                for (i = 0; i < nsems; i++) {
                        if (sem_io[i] > SEMVMX) {
-                               ipc_rcu_putref(sma, sem_rcu_free);
+                               ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
                                err = -ERANGE;
                                goto out_free;
                        }
@@ -1699,7 +1699,7 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
        }
 
        nsems = sma->sem_nsems;
-       if (!ipc_rcu_getref(sma)) {
+       if (!ipc_rcu_getref(&sma->sem_perm)) {
                rcu_read_unlock();
                un = ERR_PTR(-EIDRM);
                goto out;
@@ -1709,7 +1709,7 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
        /* step 2: allocate new undo structure */
        new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
        if (!new) {
-               ipc_rcu_putref(sma, sem_rcu_free);
+               ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
                return ERR_PTR(-ENOMEM);
        }
 

diff --git a/ipc/shm.c b/ipc/shm.c
index f45c795..5ef6d31 100644 (file)
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -174,9 +174,10 @@ static inline void shm_lock_by_ptr(struct shmid_kernel *ipcp)
 
 static void shm_rcu_free(struct rcu_head *head)
 {
-       struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
-       struct shmid_kernel *shp = ipc_rcu_to_struct(p);
-
+       struct kern_ipc_perm *ptr = container_of(head, struct kern_ipc_perm,
+                                                       rcu);
+       struct shmid_kernel *shp = container_of(ptr, struct shmid_kernel,
+                                                       shm_perm);
        security_shm_free(shp);
        ipc_rcu_free(head);
 }
@@ -241,7 +242,7 @@ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
                user_shm_unlock(i_size_read(file_inode(shm_file)),
                                shp->mlock_user);
        fput(shm_file);
-       ipc_rcu_putref(shp, shm_rcu_free);
+       ipc_rcu_putref(&shp->shm_perm, shm_rcu_free);
 }
 
 /*
@@ -542,7 +543,10 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
                        ns->shm_tot + numpages > ns->shm_ctlall)
                return -ENOSPC;
 
-       shp = ipc_rcu_alloc(sizeof(*shp));
+       BUILD_BUG_ON(offsetof(struct shmid_kernel, shm_perm) != 0);
+
+       shp = container_of(ipc_rcu_alloc(sizeof(*shp)), struct shmid_kernel,
+                               shm_perm);
        if (!shp)
                return -ENOMEM;
 
@@ -553,7 +557,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
        shp->shm_perm.security = NULL;
        error = security_shm_alloc(shp);
        if (error) {
-               ipc_rcu_putref(shp, ipc_rcu_free);
+               ipc_rcu_putref(&shp->shm_perm, ipc_rcu_free);
                return error;
        }
 
@@ -624,7 +628,7 @@ no_id:
                user_shm_unlock(size, shp->mlock_user);
        fput(file);
 no_file:
-       ipc_rcu_putref(shp, shm_rcu_free);
+       ipc_rcu_putref(&shp->shm_perm, shm_rcu_free);
        return error;
 }
 

diff --git a/ipc/util.c b/ipc/util.c
index caec7b1..5d1ff10 100644 (file)
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -418,46 +418,45 @@ void ipc_free(void *ptr)
 }
 
 /**
- * ipc_rcu_alloc - allocate ipc and rcu space
+ * ipc_rcu_alloc - allocate ipc space
  * @size: size desired
  *
- * Allocate memory for the rcu header structure +  the object.
- * Returns the pointer to the object or NULL upon failure.
+ * Allocate memory for an ipc object.
+ * The first member must be struct kern_ipc_perm.
  */
-void *ipc_rcu_alloc(int size)
+struct kern_ipc_perm *ipc_rcu_alloc(int size)
 {
        /*
         * We prepend the allocation with the rcu struct
         */
-       struct ipc_rcu *out = ipc_alloc(sizeof(struct ipc_rcu) + size);
+       struct kern_ipc_perm *out = ipc_alloc(size);
        if (unlikely(!out))
                return NULL;
+
+       memset(out, 0, size);
        atomic_set(&out->refcount, 1);
-       return out + 1;
+       return out;
 }
 
-int ipc_rcu_getref(void *ptr)
+int ipc_rcu_getref(struct kern_ipc_perm *ptr)
 {
-       struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
-
-       return atomic_inc_not_zero(&p->refcount);
+       return atomic_inc_not_zero(&ptr->refcount);
 }
 
-void ipc_rcu_putref(void *ptr, void (*func)(struct rcu_head *head))
+void ipc_rcu_putref(struct kern_ipc_perm *ptr,
+                       void (*func)(struct rcu_head *head))
 {
-       struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
-
-       if (!atomic_dec_and_test(&p->refcount))
+       if (!atomic_dec_and_test(&ptr->refcount))
                return;
 
-       call_rcu(&p->rcu, func);
+       call_rcu(&ptr->rcu, func);
 }
 
-void ipc_rcu_free(struct rcu_head *head)
+void ipc_rcu_free(struct rcu_head *h)
 {
-       struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
+       struct kern_ipc_perm *ptr = container_of(h, struct kern_ipc_perm, rcu);
 
-       kvfree(p);
+       kvfree(ptr);
 }
 
 /**

diff --git a/ipc/util.h b/ipc/util.h
index 60ddccc..09d0f91 100644 (file)
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -47,13 +47,6 @@ static inline void msg_exit_ns(struct ipc_namespace *ns) { }
 static inline void shm_exit_ns(struct ipc_namespace *ns) { }
 #endif
 
-struct ipc_rcu {
-       struct rcu_head rcu;
-       atomic_t refcount;
-} ____cacheline_aligned_in_smp;
-
-#define ipc_rcu_to_struct(p)  ((void *)(p+1))
-
 /*
  * Structure that holds the parameters needed by the ipc operations
  * (see after)
@@ -125,11 +118,14 @@ void ipc_free(void *ptr);
  * Objects are reference counted, they start with reference count 1.
  * getref increases the refcount, the putref call that reduces the recount
  * to 0 schedules the rcu destruction. Caller must guarantee locking.
+ *
+ * struct kern_ipc_perm must be the first member in the allocated structure.
  */
-void *ipc_rcu_alloc(int size);
-int ipc_rcu_getref(void *ptr);
-void ipc_rcu_putref(void *ptr, void (*func)(struct rcu_head *head));
-void ipc_rcu_free(struct rcu_head *head);
+struct kern_ipc_perm *ipc_rcu_alloc(int size);
+int ipc_rcu_getref(struct kern_ipc_perm *ptr);
+void ipc_rcu_putref(struct kern_ipc_perm *ptr,
+                       void (*func)(struct rcu_head *head));
+void ipc_rcu_free(struct rcu_head *h);
 
 struct kern_ipc_perm *ipc_lock(struct ipc_ids *, int);
 struct kern_ipc_perm *ipc_obtain_object_idr(struct ipc_ids *ids, int id);