From: Eric W. Biederman <ebiederm@xmission.com>

I just refactored fs/proc/base.c to use task_refs to ensure there are not
long user triggerable hold times of task_struct.  It looks like I missed
cpuset.c.  Oops.

This patch updates proc_cpuset_show to handle the task dying between when
the file is opened and when data is read out.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 kernel/cpuset.c |   32 +++++++++++++++++++++-----------
 1 files changed, 21 insertions(+), 11 deletions(-)

diff -puN kernel/cpuset.c~proc-dont-lock-task_structs-indefinitely-cpuset-fix-2 kernel/cpuset.c
--- devel/kernel/cpuset.c~proc-dont-lock-task_structs-indefinitely-cpuset-fix-2	2006-02-28 17:18:27.000000000 -0800
+++ devel-akpm/kernel/cpuset.c	2006-02-28 17:18:27.000000000 -0800
@@ -49,6 +49,7 @@
 #include <linux/time.h>
 #include <linux/backing-dev.h>
 #include <linux/sort.h>
+#include <linux/task_ref.h>
 
 #include <asm/uaccess.h>
 #include <asm/atomic.h>
@@ -2379,37 +2380,46 @@ void __cpuset_memory_pressure_bump(void)
 static int proc_cpuset_show(struct seq_file *m, void *v)
 {
 	struct cpuset *cs;
+	struct task_ref *tref;
 	struct task_struct *tsk;
 	char *buf;
-	int retval = 0;
+	int retval;
 
+	retval = -ENOMEM;
 	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
 	if (!buf)
-		return -ENOMEM;
+		goto out;
+
+	retval = -ESRCH;
+	tref = m->private;
+	tsk = get_tref_task(tref);
+	if (!tsk)
+		goto out_free;
 
-	tsk = m->private;
+	retval = -EINVAL;
 	mutex_lock(&manage_mutex);
 	cs = tsk->cpuset;
-	if (!cs) {
-		retval = -EINVAL;
-		goto out;
-	}
+	if (!cs)
+		goto out_unlock;
 
 	retval = cpuset_path(cs, buf, PAGE_SIZE);
 	if (retval < 0)
-		goto out;
+		goto out_unlock;
 	seq_puts(m, buf);
 	seq_putc(m, '\n');
-out:
+out_unlock:
 	mutex_unlock(&manage_mutex);
+	put_task_struct(tsk);
+out_free:
 	kfree(buf);
+out:
 	return retval;
 }
 
 static int cpuset_open(struct inode *inode, struct file *file)
 {
-	struct task_struct *tsk = PROC_I(inode)->task;
-	return single_open(file, proc_cpuset_show, tsk);
+	struct task_ref *tref = PROC_I(inode)->tref;
+	return single_open(file, proc_cpuset_show, tref);
 }
 
 struct file_operations proc_cpuset_operations = {
_