diff options
| author | Davidlohr Bueso <davidlohr@hp.com> | 2013-10-16 22:46:45 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-10-17 06:35:52 +0200 |
| commit | 18ccee263c7e250a57f01c9434658f11f4118a64 (patch) | |
| tree | 1655243afdaed94d9e2bdb50af14e45e1cc92834 /ipc | |
| parent | mm, memcg: protect mem_cgroup_read_events for cpu hotplug (diff) | |
| download | linux-18ccee263c7e250a57f01c9434658f11f4118a64.tar.xz linux-18ccee263c7e250a57f01c9434658f11f4118a64.zip | |
ipc: update locking scheme comments
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>
Diffstat (limited to 'ipc')
| -rw-r--r-- | ipc/util.c | 27 |
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> |