From 6ff2d39b91aec3dcae951afa982059e3dd9b49dc Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Mon, 1 Dec 2008 13:14:02 -0800 Subject: [PATCH] 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 Cc: Clement Calmels Cc: Nadia Derbey Cc: Pierre Peiffer Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/idr.h | 3 ++- lib/idr.c | 14 ++++++++++++-- 2 files changed, 14 insertions(+), 3 deletions(-) diff --git a/include/linux/idr.h b/include/linux/idr.h index fa035f96f2a3..dd846df8cd32 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<layer = l-1; rcu_assign_pointer(p->ary[m], new); p->count++; } @@ -210,6 +211,7 @@ build_up: if (unlikely(!p)) { if (!(p = get_from_free_list(idp))) return -1; + p->layer = 0; layers = 1; } /* @@ -237,6 +239,7 @@ build_up: } new->ary[0] = p; new->count = 1; + new->layer = layers-1; if (p->bitmap == IDR_FULL) __set_bit(0, &new->bitmap); p = new; @@ -493,17 +496,21 @@ void *idr_find(struct idr *idp, int id) int n; struct idr_layer *p; - n = idp->layers * IDR_BITS; p = rcu_dereference(idp->top); + if (!p) + return NULL; + n = (p->layer+1) * IDR_BITS; /* Mask off upper bits we don't use for the search. */ id &= MAX_ID_MASK; if (id >= (1 << n)) return NULL; + BUG_ON(n == 0); while (n > 0 && p) { n -= IDR_BITS; + BUG_ON(n != p->layer*IDR_BITS); p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]); } return((void *)p); @@ -582,8 +589,11 @@ void *idr_replace(struct idr *idp, void *ptr, int id) int n; struct idr_layer *p, *old_p; - n = idp->layers * IDR_BITS; p = idp->top; + if (!p) + return ERR_PTR(-EINVAL); + + n = (p->layer+1) * IDR_BITS; id &= MAX_ID_MASK;