aboutsummaryrefslogtreecommitdiff
path: root/ipc
diff options
context:
space:
mode:
authorDavidlohr Bueso <davidlohr@hp.com>2013-10-16 13:46:45 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-12-04 10:56:12 -0800
commit3f47cff85a8737780a5eba628cae112cd07496de (patch)
tree327ad323bef9151d79312a43b90f19045fb58c10 /ipc
parenta12503f53b7555a639869527d47eef61ff33cd00 (diff)
downloadlinaro-lsk-3f47cff85a8737780a5eba628cae112cd07496de.tar.gz
ipc: update locking scheme comments
commit 18ccee263c7e250a57f01c9434658f11f4118a64 upstream. The initial documentation was a bit incomplete, update accordingly. [akpm@linux-foundation.org: make it more readable in 80 columns] Signed-off-by: Davidlohr Bueso <davidlohr@hp.com> Acked-by: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'ipc')
-rw-r--r--ipc/util.c27
1 files changed, 21 insertions, 6 deletions
diff --git a/ipc/util.c b/ipc/util.c
index fdb8ae74077..7684f41bce7 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>