From 35991ed9581955016ee2349f5f6fc8b1eb301183 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Tue, 18 Nov 2008 15:23:08 +0100
Subject: [PATCH] --- yaml --- r: 119211 b: refs/heads/master c:
 10db4ef7b9a65b86e4d047671a1886f4c101a859 h: refs/heads/master i:   119209:
 50a1311d0ef6b12b5f359ba1949904d530d71902   119207:
 22ee6b73340ae8060c14c510ab4bd4ed0eb42677 v: v3

---
 [refs]                     |  2 +-
 trunk/arch/x86/kernel/ds.c | 26 +++++++++++++++++++++-----
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/[refs] b/[refs]
index ac223a693011..9bd92f797a67 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 93ce99e849433ede4ce8b410b749dc0cad1100b2
+refs/heads/master: 10db4ef7b9a65b86e4d047671a1886f4c101a859
diff --git a/trunk/arch/x86/kernel/ds.c b/trunk/arch/x86/kernel/ds.c
index ac1d5b0586ba..d1a121443bde 100644
--- a/trunk/arch/x86/kernel/ds.c
+++ b/trunk/arch/x86/kernel/ds.c
@@ -236,17 +236,33 @@ static inline struct ds_context *ds_alloc_context(struct task_struct *task)
 	struct ds_context *context = *p_context;
 
 	if (!context) {
+		spin_unlock(&ds_lock);
+
 		context = kzalloc(sizeof(*context), GFP_KERNEL);
 
-		if (!context)
+		if (!context) {
+			spin_lock(&ds_lock);
 			return NULL;
+		}
 
 		context->ds = kzalloc(ds_cfg.sizeof_ds, GFP_KERNEL);
 		if (!context->ds) {
 			kfree(context);
+			spin_lock(&ds_lock);
 			return NULL;
 		}
 
+		spin_lock(&ds_lock);
+		/*
+		 * Check for race - another CPU could have allocated
+		 * it meanwhile:
+		 */
+		if (*p_context) {
+			kfree(context->ds);
+			kfree(context);
+			return *p_context;
+		}
+
 		*p_context = context;
 
 		context->this = p_context;
@@ -384,15 +400,15 @@ static int ds_request(struct task_struct *task, void *base, size_t size,
 
 	spin_lock(&ds_lock);
 
-	error = -EPERM;
-	if (!check_tracer(task))
-		goto out_unlock;
-
 	error = -ENOMEM;
 	context = ds_alloc_context(task);
 	if (!context)
 		goto out_unlock;
 
+	error = -EPERM;
+	if (!check_tracer(task))
+		goto out_unlock;
+
 	error = -EALREADY;
 	if (context->owner[qual] == current)
 		goto out_unlock;