linux-kernel - [PATCH v3] kernel/resource.c: fix stack overflow in __reserve_region_with

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Message-Id: <1347055699-3468-1-git-send-email-tmac@hp.com>
Date:	Fri,  7 Sep 2012 16:08:19 -0600
From:	T Makphaibulchoke <tmac@...com>
To:	akpm@...ux-foundation.org, linuxram@...ibm.com,
	paul.gortmaker@...driver.com, weiyang@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Cc:	T Makphaibulchoke <tmac@...com>
Subject: [PATCH v3] kernel/resource.c: fix stack overflow in __reserve_region_with_split

Using recurvise call to try adding a non-conflicting region in the function
__reserve_region_with_split() could result in a stack overflow in the case
that the recursive calls are too deep.  Convert the recursive calls to
an iterative loop to avoid the problem.

Tested on a machine containing 135 regions.  The kernel no longer panicked
with stack overflow.

Also tested with code arbitrarily adding regions with no conflict, embedding
two consecutive conflicts and embedding two non-consecutive conflicts.

Signed-off-by: T Makphaibulchoke <tmac@...com>

---
Change since v2:
* Initializing both the name and flags fileds of the newly allocated region
  request.

Change since v1:
* Fixing __resrve_region_with_split() to ensure a reqion reserve request is
  satisfied to the fullest extent, minus any overlapping conflicting regions.
---
 kernel/resource.c |   50 ++++++++++++++++++++++++++++++++++++++------------
 1 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index 34d4588..73f35d4 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -763,6 +763,7 @@ static void __init __reserve_region_with_split(struct resource *root,
 	struct resource *parent = root;
 	struct resource *conflict;
 	struct resource *res = kzalloc(sizeof(*res), GFP_ATOMIC);
+	struct resource *next_res = NULL;
 
 	if (!res)
 		return;
@@ -772,21 +773,46 @@ static void __init __reserve_region_with_split(struct resource *root,
 	res->end = end;
 	res->flags = IORESOURCE_BUSY;
 
-	conflict = __request_resource(parent, res);
-	if (!conflict)
-		return;
+	while (1) {
 
-	/* failed, split and try again */
-	kfree(res);
+		conflict = __request_resource(parent, res);
+		if (!conflict) {
+			if (!next_res)
+				break;
+			res = next_res;
+			next_res = NULL;
+			continue;
+		}
 
-	/* conflict covered whole area */
-	if (conflict->start <= start && conflict->end >= end)
-		return;
+		/* conflict covered whole area */
+		if (conflict->start <= res->start &&
+				conflict->end >= res->end) {
+			kfree(res);
+			WARN_ON(next_res);
+			break;
+		}
+
+		/* failed, split and try again */
+		if (conflict->start > res->start) {
+			end = res->end;
+			res->end = conflict->start - 1;
+			if (conflict->end < end) {
+				next_res = kzalloc(sizeof(*next_res),
+						GFP_ATOMIC);
+				if (!next_res) {
+					kfree(res);
+					break;
+				}
+				next_res->name = name;
+				next_res->start = conflict->end + 1;
+				next_res->end = end;
+				next_res->flags = IORESOURCE_BUSY;
+			}
+		} else {
+			res->start = conflict->end + 1;
+		}
+	}
 
-	if (conflict->start > start)
-		__reserve_region_with_split(root, start, conflict->start-1, name);
-	if (conflict->end < end)
-		__reserve_region_with_split(root, conflict->end+1, end, name);
 }
 
 void __init reserve_region_with_split(struct resource *root,
-- 
1.7.1

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