signals: move cred_guard_mutex from task_struct to signal_struct

Oleg Nesterov pointed out we have to prevent multiple-threads-inside-exec
itself and we can reuse ->cred_guard_mutex for it.  Yes, concurrent
execve() has no worth.

Let's move ->cred_guard_mutex from task_struct to signal_struct.  It
naturally prevent multiple-threads-inside-exec.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index ea7ce0215cd1..99bbaa3e5b0d 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -181,7 +181,7 @@ int ptrace_attach(struct task_struct *task)
          * under ptrace.
          */
         retval = -ERESTARTNOINTR;
-        if (mutex_lock_interruptible(&task->cred_guard_mutex))
+        if (mutex_lock_interruptible(&task->signal->cred_guard_mutex))
                 goto out;
 
         task_lock(task);
@@ -208,7 +208,7 @@ int ptrace_attach(struct task_struct *task)
 unlock_tasklist:
         write_unlock_irq(&tasklist_lock);
 unlock_creds:
-        mutex_unlock(&task->cred_guard_mutex);
+        mutex_unlock(&task->signal->cred_guard_mutex);
 out:
         return retval;
 }