[PATCH] fork.c: fix NULL pointer dereference when nr_threads == threads-max

[David Howells <dhowells@redhat.com>]

From: Li Zefan <lizf@cn.fujitsu.com>

I happened to forked lots of processes, and hit NULL pointer dereference.
It is because in copy_process() after checking max_threads, 0 is returned
but not -EAGAIN.

The bug is introduced by this patch:

| commit f1752eec6145c97163dbce62d17cf5d928e28a27
| Author: David Howells <dhowells@redhat.com>
| Date:   Fri Nov 14 10:39:17 2008 +1100
|
|    CRED: Detach the credentials from task_struct

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---

 kernel/fork.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)


diff --git a/kernel/fork.c b/kernel/fork.c
index bf0cef8..586874d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1007,6 +1007,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	 * triggers too late. This doesn't hurt, the check is only there
 	 * to stop root fork bombs.
 	 */
+	retval = -EAGAIN;
 	if (nr_threads >= max_threads)
 		goto bad_fork_cleanup_count;