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-rw-r--r--ipc/util.c27
1 files changed, 21 insertions, 6 deletions
diff --git a/ipc/util.c b/ipc/util.c
index fdb8ae740775..7684f41bce76 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>

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