From 069385c15e3c22f03746fb1a2a48194a2ef6ab03 Mon Sep 17 00:00:00 2001
From: Paul Jackson <pj@sgi.com>
Date: Sun, 23 Jul 2006 11:36:08 -0700
Subject: [PATCH] --- yaml --- r: 32799 b: refs/heads/master c:
 abb5a5cc6bba1516403146c5b79036fe843beb70 h: refs/heads/master i:   32797:
 eb64114ccaff442d0a0436e9cb86a9781ec6aaa0   32795:
 0bbb6b15f5485c8ddab8a40b4dcd437992779f00   32791:
 b903f6da7965a24e4707b878864904896cbea1e4   32783:
 e24275c3568c4d4a8828527ce44f4c12c7753d98   32767:
 5ae4f0356026b0363efef5eff8fdbdc7fb85add4 v: v3

---
 [refs]                |  2 +-
 trunk/kernel/cpuset.c | 24 +++++++++++++++++++++---
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/[refs] b/[refs]
index 34b952179af9..1acc92614506 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: aa95387774039096c11803c04011f1aa42d85758
+refs/heads/master: abb5a5cc6bba1516403146c5b79036fe843beb70
diff --git a/trunk/kernel/cpuset.c b/trunk/kernel/cpuset.c
index c232dc077438..1a649f2bb9bb 100644
--- a/trunk/kernel/cpuset.c
+++ b/trunk/kernel/cpuset.c
@@ -762,6 +762,8 @@ static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
  *
  * Call with manage_mutex held.  May nest a call to the
  * lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
+ * Must not be called holding callback_mutex, because we must
+ * not call lock_cpu_hotplug() while holding callback_mutex.
  */
 
 static void update_cpu_domains(struct cpuset *cur)
@@ -781,7 +783,7 @@ static void update_cpu_domains(struct cpuset *cur)
 		if (is_cpu_exclusive(c))
 			cpus_andnot(pspan, pspan, c->cpus_allowed);
 	}
-	if (is_removed(cur) || !is_cpu_exclusive(cur)) {
+	if (!is_cpu_exclusive(cur)) {
 		cpus_or(pspan, pspan, cur->cpus_allowed);
 		if (cpus_equal(pspan, cur->cpus_allowed))
 			return;
@@ -1917,6 +1919,17 @@ static int cpuset_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 	return cpuset_create(c_parent, dentry->d_name.name, mode | S_IFDIR);
 }
 
+/*
+ * Locking note on the strange update_flag() call below:
+ *
+ * If the cpuset being removed is marked cpu_exclusive, then simulate
+ * turning cpu_exclusive off, which will call update_cpu_domains().
+ * The lock_cpu_hotplug() call in update_cpu_domains() must not be
+ * made while holding callback_mutex.  Elsewhere the kernel nests
+ * callback_mutex inside lock_cpu_hotplug() calls.  So the reverse
+ * nesting would risk an ABBA deadlock.
+ */
+
 static int cpuset_rmdir(struct inode *unused_dir, struct dentry *dentry)
 {
 	struct cpuset *cs = dentry->d_fsdata;
@@ -1936,11 +1949,16 @@ static int cpuset_rmdir(struct inode *unused_dir, struct dentry *dentry)
 		mutex_unlock(&manage_mutex);
 		return -EBUSY;
 	}
+	if (is_cpu_exclusive(cs)) {
+		int retval = update_flag(CS_CPU_EXCLUSIVE, cs, "0");
+		if (retval < 0) {
+			mutex_unlock(&manage_mutex);
+			return retval;
+		}
+	}
 	parent = cs->parent;
 	mutex_lock(&callback_mutex);
 	set_bit(CS_REMOVED, &cs->flags);
-	if (is_cpu_exclusive(cs))
-		update_cpu_domains(cs);
 	list_del(&cs->sibling);	/* delete my sibling from parent->children */
 	spin_lock(&cs->dentry->d_lock);
 	d = dget(cs->dentry);