Subject: + ipc-update-locking-scheme-comments.patch added to -mm tree
To: davidlohr@xxxxxx,manfred@xxxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Thu, 03 Oct 2013 12:36:40 -0700
The patch titled
Subject: ipc: update locking scheme comments
has been added to the -mm tree. Its filename is
ipc-update-locking-scheme-comments.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipc-update-locking-scheme-comments.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipc-update-locking-scheme-comments.patch
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------------------------------------------------------
From: Davidlohr Bueso <davidlohr@xxxxxx>
Subject: ipc: update locking scheme comments
The initial documentation was a bit incomplete, update accordingly.
Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
Acked-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/util.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff -puN ipc/util.c~ipc-update-locking-scheme-comments ipc/util.c
--- a/ipc/util.c~ipc-update-locking-scheme-comments
+++ a/ipc/util.c
@@ -17,12 +17,21 @@
* 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)
+ * 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 /proc/sysvipc/* files.
+ *
+ * Note that sems have a special fast path that avoids kern_ipc_perm.lock - see sem_lock().
*/
#include <linux/mm.h>
_
Patches currently in -mm which might be from davidlohr@xxxxxx are
origin.patch
ipc-update-locking-scheme-comments.patch
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