From 6ff2d39b91aec3dcae951afa982059e3dd9b49dc Mon Sep 17 00:00:00 2001
From: Manfred Spraul <manfred@colorfullife.com>
Date: Mon, 1 Dec 2008 13:14:02 -0800
Subject: lib/idr.c: fix rcu related race with idr_find

2nd part of the fixes needed for
http://bugzilla.kernel.org/show_bug.cgi?id=11796.

When the idr tree is either grown or shrunk, then the update to the number
of layers and the top pointer were not atomic.  This race caused crashes.

The attached patch fixes that by replicating the layers counter in each
layer, thus idr_find doesn't need idp->layers anymore.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Clement Calmels <cboulte@gmail.com>
Cc: Nadia Derbey <Nadia.Derbey@bull.net>
Cc: Pierre Peiffer <peifferp@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 include/linux/idr.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to 'include')

diff --git a/include/linux/idr.h b/include/linux/idr.h
index fa035f96f2a..dd846df8cd3 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -52,13 +52,14 @@ struct idr_layer {
 	unsigned long		 bitmap; /* A zero bit means "space here" */
 	struct idr_layer	*ary[1<<IDR_BITS];
 	int			 count;	 /* When zero, we can release it */
+	int			 layer;	 /* distance from leaf */
 	struct rcu_head		 rcu_head;
 };
 
 struct idr {
 	struct idr_layer *top;
 	struct idr_layer *id_free;
-	int		  layers;
+	int		  layers; /* only valid without concurrent changes */
 	int		  id_free_cnt;
 	spinlock_t	  lock;
 };
-- 
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