From 05603c44a7627793219b0bd9a7b236099dc9cd9d Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <davidlohr.bueso@hp.com>
Date: Wed, 11 Sep 2013 14:26:26 -0700
Subject: [PATCH] ipc: document general ipc locking scheme

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>
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