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ipc: document general ipc locking scheme

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As suggested by Andrew, add a generic initial locking scheme used
throughout all sysv ipc mechanisms.  Documenting the ids rwsem, how rcu
can be enough to do the initial checks and when to actually acquire the
kern_ipc_perm.lock spinlock.

I found that adding it to util.c was generic enough.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Davidlohr Bueso 2013-09-11 14:26:26 -07:00 committed by Linus Torvalds
parent 4718787d1f
commit 05603c44a7
1 changed files with 8 additions and 0 deletions
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8
ipc/util.c
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@ -15,6 +15,14 @@
* Jun 2006 - namespaces ssupport
* OpenVZ, SWsoft Inc.
* 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)
*/
#include <linux/mm.h>