This is a note to let you know that I've just added the patch titled
ipc: update locking scheme comments
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ipc-update-locking-scheme-comments.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 18ccee263c7e250a57f01c9434658f11f4118a64 Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <davidlohr@xxxxxx>
Date: Wed, 16 Oct 2013 13:46:45 -0700
Subject: ipc: update locking scheme comments
From: Davidlohr Bueso <davidlohr@xxxxxx>
commit 18ccee263c7e250a57f01c9434658f11f4118a64 upstream.
The initial documentation was a bit incomplete, update accordingly.
[akpm@xxxxxxxxxxxxxxxxxxxx: make it more readable in 80 columns]
Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
Acked-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
ipc/util.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -17,12 +17,27 @@
* Pavel Emelianov <xemul@xxxxxxxxxx>
*
* 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>
Patches currently in stable-queue which might be from davidlohr@xxxxxx are
queue-3.10/ipc-msg-fix-message-length-check-for-negative-values.patch
queue-3.10/ipc-update-locking-scheme-comments.patch
queue-3.10/ipc-sem.c-synchronize-semop-and-semctl-with-ipc_rmid.patch
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