diff options
author | Paul E. McKenney <paulmck@us.ibm.com> | 2004-10-27 18:28:37 -0700 |
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committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2004-10-27 18:28:37 -0700 |
commit | 3f9fabe7e676a768b70c662f334f3b290ed0907e (patch) | |
tree | 2263d4c76d12037ec0e0d6ba0c3976474c8c17a3 /ipc | |
parent | fa56b76fabdfdff9f8bcb8831ea9e7b4f76eddaf (diff) | |
download | history-3f9fabe7e676a768b70c662f334f3b290ed0907e.tar.gz |
[PATCH] RCU: eliminating explicit memory barriers from SysV IPC
This patch uses the rcu_assign_pointer() API to eliminate a number of explicit
memory barriers from the SysV IPC code that uses RCU. It also restructures
the ipc_ids structure so that the array size is stored in the same memory
block as the array itself (see the new struct ipc_id_ary). This prevents the
race that the earlier code was subject to, where a reader could see a mismatch
between the size and the actual array. With the size stored with the array,
the possibility of mismatch is eliminated -- with out the need for careful
ordering and explicit memory barriers. This has been tested successfully on
i386 and ppc64.
Signed-off-by: <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'ipc')
-rw-r--r-- | ipc/msg.c | 2 | ||||
-rw-r--r-- | ipc/sem.c | 2 | ||||
-rw-r--r-- | ipc/util.c | 80 | ||||
-rw-r--r-- | ipc/util.h | 13 |
4 files changed, 45 insertions, 52 deletions
diff --git a/ipc/msg.c b/ipc/msg.c index 93d46e9352f627..7d7470c8d2c253 100644 --- a/ipc/msg.c +++ b/ipc/msg.c @@ -381,7 +381,7 @@ asmlinkage long sys_msgctl (int msqid, int cmd, struct msqid_ds __user *buf) int success_return; if (!buf) return -EFAULT; - if(cmd == MSG_STAT && msqid >= msg_ids.size) + if(cmd == MSG_STAT && msqid >= msg_ids.entries->size) return -EINVAL; memset(&tbuf,0,sizeof(tbuf)); diff --git a/ipc/sem.c b/ipc/sem.c index 06f756db359aeb..7d639d9f131ed9 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -524,7 +524,7 @@ static int semctl_nolock(int semid, int semnum, int cmd, int version, union semu struct semid64_ds tbuf; int id; - if(semid >= sem_ids.size) + if(semid >= sem_ids.entries->size) return -EINVAL; memset(&tbuf,0,sizeof(tbuf)); diff --git a/ipc/util.c b/ipc/util.c index a6c797431f0620..62be4a26fe882a 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -62,7 +62,6 @@ void __init ipc_init_ids(struct ipc_ids* ids, int size) if(size > IPCMNI) size = IPCMNI; - ids->size = size; ids->in_use = 0; ids->max_id = -1; ids->seq = 0; @@ -74,14 +73,17 @@ void __init ipc_init_ids(struct ipc_ids* ids, int size) ids->seq_max = seq_limit; } - ids->entries = ipc_rcu_alloc(sizeof(struct ipc_id)*size); + 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"); - ids->size = 0; + size = 0; + ids->entries = &ids->nullentry; } - for(i=0;i<ids->size;i++) - ids->entries[i].p = NULL; + ids->entries->size = size; + for(i=0;i<size;i++) + ids->entries->p[i] = NULL; } /** @@ -104,7 +106,7 @@ int ipc_findkey(struct ipc_ids* ids, key_t key) * since ipc_ids.sem is held */ for (id = 0; id <= max_id; id++) { - p = ids->entries[id].p; + p = ids->entries->p[id]; if(p==NULL) continue; if (key == p->key) @@ -118,36 +120,36 @@ int ipc_findkey(struct ipc_ids* ids, key_t key) */ static int grow_ary(struct ipc_ids* ids, int newsize) { - struct ipc_id* new; - struct ipc_id* old; + struct ipc_id_ary* new; + struct ipc_id_ary* old; int i; + int size = ids->entries->size; if(newsize > IPCMNI) newsize = IPCMNI; - if(newsize <= ids->size) + if(newsize <= size) return newsize; - new = ipc_rcu_alloc(sizeof(struct ipc_id)*newsize); + new = ipc_rcu_alloc(sizeof(struct kern_ipc_perm *)*newsize + + sizeof(struct ipc_id_ary)); if(new == NULL) - return ids->size; - memcpy(new, ids->entries, sizeof(struct ipc_id)*ids->size); - for(i=ids->size;i<newsize;i++) { - new[i].p = NULL; + return size; + new->size = newsize; + memcpy(new->p, ids->entries->p, sizeof(struct kern_ipc_perm *)*size + + sizeof(struct ipc_id_ary)); + for(i=size;i<newsize;i++) { + new->p[i] = NULL; } old = ids->entries; /* - * before setting the ids->entries to the new array, there must be a - * smp_wmb() to make sure the memcpyed contents of the new array are - * visible before the new array becomes visible. + * Use rcu_assign_pointer() to make sure the memcpyed contents + * of the new array are visible before the new array becomes visible. */ - smp_wmb(); /* prevent seeing new array uninitialized. */ - ids->entries = new; - smp_wmb(); /* prevent indexing into old array based on new size. */ - ids->size = newsize; + rcu_assign_pointer(ids->entries, new); ipc_rcu_putref(old); - return ids->size; + return newsize; } /** @@ -175,7 +177,7 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size) * ipc_ids.sem is held */ for (id = 0; id < size; id++) { - if(ids->entries[id].p == NULL) + if(ids->entries->p[id] == NULL) goto found; } return -1; @@ -195,7 +197,7 @@ found: new->deleted = 0; rcu_read_lock(); spin_lock(&new->lock); - ids->entries[id].p = new; + ids->entries->p[id] = new; return id; } @@ -216,15 +218,15 @@ struct kern_ipc_perm* ipc_rmid(struct ipc_ids* ids, int id) { struct kern_ipc_perm* p; int lid = id % SEQ_MULTIPLIER; - if(lid >= ids->size) + if(lid >= ids->entries->size) BUG(); /* * do not need a rcu_dereference()() here to force ordering * on Alpha, since the ipc_ids.sem is held. */ - p = ids->entries[lid].p; - ids->entries[lid].p = NULL; + p = ids->entries->p[lid]; + ids->entries->p[lid] = NULL; if(p==NULL) BUG(); ids->in_use--; @@ -234,7 +236,7 @@ struct kern_ipc_perm* ipc_rmid(struct ipc_ids* ids, int id) lid--; if(lid == -1) break; - } while (ids->entries[lid].p == NULL); + } while (ids->entries->p[lid] == NULL); ids->max_id = lid; } p->deleted = 1; @@ -493,9 +495,9 @@ struct kern_ipc_perm* ipc_get(struct ipc_ids* ids, int id) { struct kern_ipc_perm* out; int lid = id % SEQ_MULTIPLIER; - if(lid >= ids->size) + if(lid >= ids->entries->size) return NULL; - out = ids->entries[lid].p; + out = ids->entries->p[lid]; return out; } @@ -503,25 +505,15 @@ struct kern_ipc_perm* ipc_lock(struct ipc_ids* ids, int id) { struct kern_ipc_perm* out; int lid = id % SEQ_MULTIPLIER; - struct ipc_id* entries; + struct ipc_id_ary* entries; rcu_read_lock(); - if(lid >= ids->size) { + entries = rcu_dereference(ids->entries); + if(lid >= entries->size) { rcu_read_unlock(); return NULL; } - - /* - * Note: The following two read barriers are corresponding - * to the two write barriers in grow_ary(). They guarantee - * the writes are seen in the same order on the read side. - * smp_rmb() has effect on all CPUs. rcu_dereference() - * is used if there are data dependency between two reads, and - * has effect only on Alpha. - */ - smp_rmb(); /* prevent indexing old array with new size */ - entries = rcu_dereference(ids->entries); - out = entries[lid].p; + out = entries->p[lid]; if(out == NULL) { rcu_read_unlock(); return NULL; diff --git a/ipc/util.h b/ipc/util.h index 3b3adb2d54b431..07d689452363a6 100644 --- a/ipc/util.h +++ b/ipc/util.h @@ -15,18 +15,19 @@ void sem_init (void); void msg_init (void); void shm_init (void); -struct ipc_ids { +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 semaphore sem; - struct ipc_id* entries; -}; - -struct ipc_id { - struct kern_ipc_perm* p; + struct ipc_id_ary nullentry; + struct ipc_id_ary* entries; }; void __init ipc_init_ids(struct ipc_ids* ids, int size); |