diff options
Diffstat (limited to 'ipc/util.c')
| -rw-r--r-- | ipc/util.c | 31 |
1 files changed, 22 insertions, 9 deletions
diff --git a/ipc/util.c b/ipc/util.c index fdb8ae740775..3ae17a4ace5b 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -17,12 +17,27 @@ * Pavel Emelianov <xemul@openvz.org> * * General sysv ipc locking scheme: - * when doing ipc id lookups, take the ids->rwsem - * rcu_read_lock() - * obtain the ipc object (kern_ipc_perm) - * perform security, capabilities, auditing and permission checks, etc. - * acquire the ipc lock (kern_ipc_perm.lock) throught ipc_lock_object() - * perform data updates (ie: SET, RMID, LOCK/UNLOCK commands) + * rcu_read_lock() + * obtain the ipc object (kern_ipc_perm) by looking up the id in an idr + * tree. + * - perform initial checks (capabilities, auditing and permission, + * etc). + * - perform read-only operations, such as STAT, INFO commands. + * acquire the ipc lock (kern_ipc_perm.lock) through + * ipc_lock_object() + * - perform data updates, such as SET, RMID commands and + * mechanism-specific operations (semop/semtimedop, + * msgsnd/msgrcv, shmat/shmdt). + * drop the ipc lock, through ipc_unlock_object(). + * rcu_read_unlock() + * + * The ids->rwsem must be taken when: + * - creating, removing and iterating the existing entries in ipc + * identifier sets. + * - iterating through files under /proc/sysvipc/ + * + * Note that sems have a special fast path that avoids kern_ipc_perm.lock - + * see sem_lock(). */ #include <linux/mm.h> @@ -75,10 +90,8 @@ static int ipc_memory_callback(struct notifier_block *self, * In order not to keep the lock on the hotplug memory chain * for too long, queue a work item that will, when waken up, * activate the ipcns notification chain. - * No need to keep several ipc work items on the queue. */ - if (!work_pending(&ipc_memory_wq)) - schedule_work(&ipc_memory_wq); + schedule_work(&ipc_memory_wq); break; case MEM_GOING_ONLINE: case MEM_GOING_OFFLINE: |